Entries in Nutrition (12)

Monday
May212012

A Review of Hydration

By: Douglas S. Kalman, PhD, RD and Anna Lepeley, MS, CSCS, CISSN
From: Strength and Conditioning Journal: Vol 32 No 2 April 2010
Article link: A Review of Hydration.


This article reviews the guidelines and considerations of hydration applicable to various population groups and respective conditions. An area of interest and controversy with hydration is the impact of adding protein, as compared with carbohydrate or the combination of the two, on overall hydration and performance status.

The Institute of Medicine (IOM) in 2004 put forth official recommendations as related to water/hydration needs. this official recommendation is a new step within the paradigm of recommended dailyintake/allowance as before 2004, whenthe IOM stated that it was impossible to set a water recommendation (11). The IOM has created a level of water intake deemed to describe the ‘‘adequate intake’’ (AI). The AI is meant ‘‘to prevent deleterious, primary acute, effects of dehydration, which include metabolic and functional abnormalities’’ (11). Water is the largest constituent of the human body. It accounts formore than 60% of the human body’s volume. Water is essential for cellular homeostasis, playing important roles in physiological and biochemical functions. Many factors impact daily hydration needs and our ability tohydrate. How the body regulates and uses water/hydration is relevant to the realm of nutrition and physical activity.For example, an increase in core body temperature during exercise is coupled with heat dissipation. Heat dissipation will result in cutaneous vasodilation and change in heat transfer and exchange. If heat transfer via radiationand convection is not adequate in reducing the heat load, sweating will occur, and heat will be lost by evaporation. If the water loss exceeds fluid intake (a condition referred to as hypohydration), then dehydration will ensue.

Water is a macronutrient that is underappreciated. It has to be recognized that there is extreme difficulty in establishing a specific level of water intake that ensures adequate hydration and promotes optimal health under all potential conditions and populations. Understanding the relationship between hydration states and optimal wellness along with disease relationships allows for the belief that there is a relationship between hydration and disease. Moreover, it is believed that hydration may play a role in the prevention of prolonged labor, urolithiasis, urinary tract infections, bladder cancer, constipation, pulmonary/bronchial disorders, heart disease, hypertension, venous thrombosis, and other conditions (9,16).

The purpose of this review is to provide a basic background of information as related to the aspects that affect hydration needs and fluid balance. The provision of fluid guidelines for the physically active adult and the nonactive adult is included. Total life cycle hydration is not covered herein but may be obtained through outside resources (3).

TOPICAL OVERVIEW OF WATER

Fluid intake’s impact on health is well recognized. Surprisingly, however, the attention in which water/hydration is given is often undermined because the media infatuates with nutrition-related research focusing on carbohydrates, protein, and fat in hope of shedding light on prevalent obesity epidemics. The body is composed of 50–70% water (the average of 60% is the norm), and water/fluid is stored or circulating. For example, muscle contains about 73% water, blood 93%, and fat mass has 10%. It is known that approximately 5– 10% of total body water is turned over daily through obligatory losses (respiration, urine, and sweat). Respiratory water losses are typically recouped by the production of metabolic water formed by substrate oxidation. Fluid losses during and after exercise also affect overall fluid balance. By definition, fluid balance is the achievement of a balance between fluid output and intake. It has been reported that physically active adults who reside in warmer climates have daily water needs of 6 liters with highly active populations needing even more to remain euhydrated (32). It also appears that as we age, our hydration needs also increase (26,36). Water is a fluid that acts as a solvent and a transport system within the human body. Water can affect many metabolic processes, attributes of physical performance, and mental acuity because it plays a primary role in thermoregulation, optimal health, and its acute status. A disruption in fluid balance, as minimal as a 2% total body water reduction, can significantly hinder aerobic performance, orthostatic tolerance, and cognitive function. The average fluid intake in the United States is currently 1,440 mL/d with 19% of the fluid intake coming from foods (2).

The IOM recommends, in general, that men aged 19–70 and older consume 3.7 L/d and women aged 19–70 and older ingest 2.7 L/d of all water sources (water, other liquids, and foods). Hence, Americans are typically underhydrated based on the following IOM guidelines.

PROPERTIES OF WATER

Water is a multifunctional macronutrient. One of the utmost important functions of water is heat regulation (body heat). Water acts as a buffer when body temperature rises if there is high specific heat (the specific heat of water equals 1 when 1 kilogram of water is heated 1_C between 15 and 16_C). As aforementioned, the body is approximately 60% fluid; therefore, a 70 kg man will contain approximately 42 kg of water throughout the body (29). For every 1_ rise in temperature in a 70 kg person, approximately 58 calories (kilocalories termed herein as calories) will be metabolized, thus the heat buffering effect of water also results in increased metabolic rate. Thermoregulation is pertinent to exercise physiology (and thus, overall physical activity) as evidenced by the evaporation of sweat. For example, for every gram of sweat evaporated (liquid to vapor) from the skin, the body expends 0.58 calories (or 2.43 kJ) (29,8). In other words, there is a metabolic cost of exercise and that the caloric expenditure is related to hydration status. Therefore, water not only has high specific heat, it also assists in the transfer of heat from areas of production to dissipation. Heat transport occurs efficiently, with minimal change in actual blood temperature. The body regulates fluid balance in a precise and proficient fashion. Water readily transverses all cell membranes in the body. Osmotic and hydrostatic gradients dictate the movement of water. Water is also affected by the activity of adenosine triphosphatase in sodium-potassium pump (Na-K pump). For example, when a person initiates a regularly conducted exercise regimen and is unaccustomed to doing so, fluid shifts occur and plasma volume will expand to accommodate upon commencement.

REGULATION OF THIRST AND HYDRATION

Thirst is subjective. The perception of being thirsty is also a subjective motivator to quench the thirst in animals and humans (21). Regulatory systems maintain body fluid levels essential for long-term survival. Fluid needs and urges to drink are influenced by various and interrelated factors including cultural and societal habits, internal psychogenic drive, and the regulatory controls to maintain fluid homeostasis.

Regulatory control includes maintaining fluid content of various bodily compartments, the osmotic gradient of the extracellular fluids, or work with specific hormones to assist in the regulation. When the body loses water, it is usually depleted from both the extracellular and intracellular spaces. These losses might not be equal in volume. A loss of water and sodium chloride (NaCl), the major solute of the extracellular fluid, results in proportionately more extracellular fluid depletion than if water alone is lost. In sweat, NaCl is lost at a rate of 7:1 compared with potassium (21). Thus, fluid losses of 1–2% of body weight or greater induce the need for fluid and electrolyte replacement. If fluid losses come from the gastrointestinal tract (i.e., diarrhea) and are of normal osmotic load (isotonic), then the depletion will be entirely from the extracellular fluid. However, if hypertonic fluid is added to the extracellular compartment, there will be an osmotic depletion of water from the intracellular compartment into the extracellular fluid, and this latter compartment will be expanded. There is a range of compensatory responses that can occur in synchronicity with losses from the intra- or extracellular space. Understanding the effects of vasopressin secretion, stimulation of the renin-angiotensin-aldosterone system, sympathetic activation, and reduced renal solute and water excretion is important when addressing hydration in athletes. Hormonal responses to fluid losses, however, are not solutions to returning an athlete to a euhydrated state. The sole means of properly hydrating an individual is by replenishing by the standards of 600 mL per 0.46 kg weight loss (approximately 1,320 mL per kilogram weight lost) (11,13,17,18,23).

Thirst can be thought of as the ‘‘vocal’’ component, the body’s response to fluid shifts or losses. The regulation of thirst includes osmoregulation. The osmotic pressure of the fluid (plasma osmolality) typically lies between 280 and 295 mosmol/kg/H2O. Losses as small as 1–2% of body weight stimulates thirst. Thirst is a response to an increase in the osmotic gradient. Changes in NaCl and/or glucose induce this response by not crossing cell membranes easily.

The osmotic differences between the intracellular and extracellular spaces are what dictate the flow of fluids (higher to lower concentration occurring typically by osmosis). Osmosis is partially regulated by osmoreceptors (relative to vasopressin) in the brain and in the liver. The hypothalamus is the center of the brain where thirst regulation is dictated (14). Thirst regulation is, unquestionably, multifactorial. Within the central nervous system, osmotic, ionic, ahormonal, and nervous signals are integrated and impact the perception of thirst. Overcoming hypo- or dehydration after the ingestion of water or fluid involves additional pathways and factors that are beyond the scope of this article. Furthermore, disease or metabolic disorder states’ impact on hydration status is of noteworthy consideration that cannot be overlooked even in the apparently healthy athlete.

HYDRATION, HEALTH, AND DISEASE

Because many diseases have multifactorial origins (i.e., lifestyle, genetics, and environment), including the state of hydration, the various origins are worthy of examination. Mild dehydration is a factor in the development of various conditions and diseases. Conditions associated with the negative impacts of hypohydration or dehydration include alterations in amniotic fluids, prolonged labor, cystic fibrosis, and renal toxicity secondary to dehydration altering how contrast agents are metabolized.

The effects of chronic hypohydration or dehydration (systemic effects) include associations with (ranging from weak to mild) urinary tract infections, gallstones, constipation, hypertension, bladder and colon cancer, venous thromboembolism, cerebral infarcts, dental diseases, kidney stones, mitral valve prolapse, glaucoma, and diabetic ketoacidosis (16). Rehydration and proper hydration assist with condition management, disease prevention, and the betterment of health. Factors that can affect hydration include high ambient temperature, the relative humidity, high sweat losses (sweat rates), increased body temperature, exercise duration, training status of the individual, exercise intensity, high body fat percentage, underwater exercise, use of diuretic medications, and uncontrolled diabetes. The assessment of an athlete for hydration should include a review of all of the aforementioned factors.

The goal with each individual, regardless of athletic participation status or lack thereof, is euhydration. Hydration needs have been detailed by the IOM, as aforementioned, for both genders. However, the practicality of application is hard for the everyday consumer. Easy ‘‘rule of thumb’’ hydration guidelines for general health are needed. Many dietitians recommend their clients shoot for a goal to drink the equivalence of ounces to half their body weight. Meaning that if you weigh 68 kg (150 pounds), your hydration goal, per day, with normal activities are 1500–2250 mL (50–75 oz) of nonalcoholic fluid.

HYDRATION AND PHYSICAL AND ATHLETIC PERFORMANCES

The overwhelmingly consistent conclusion across multiple research studies, academic societies, and training associations is that dehydration can significantly impact performance, with particular concern in warmer climate conditions (6,15–17,23). Thus, fluid replacement guidelines have been established to minimize exertional dehydration. Dehydration, as defined by a 2% loss of euhydrated body weight (30), negatively impacts athletic performance. Dehydration is associated with a reduction or an adverse effect upon muscle strength, endurance, coordination, mental acuity, and the thermoregulatory processes (1,4,6,9,15–17).

Water/fluid losses during exercise are impacted by many variables. The interindividual variation in sweat rates is wide, and no universal recommendations are used. As a general rule, for every pound of body weight lost between the initiation of exercise and the cessation, one replaces with 600 mL per approximately 1/5 kilogram of body weight lost (20 ounces [1.25 pints per pound] per pound of body weight lost).

Fluid and sodium losses occur during prolonged exercise. Human sweat contains 40–50 mmol sodium per liter (30). For the most part, in the normal healthy person, large fluid losses are followed by large sodium losses. The typical sodium to potassium ratio of losses is 7:1. An athlete engaged in prolonged exercise can lose 5 L of fluid per day with a range of 4,600–5,750 mg sodium and much smaller amounts of potassium. Heat-acclimated athletes benefit from enhanced sodium reabsorption that results in better protection of plasma volume by reducing the sodium losses. The training state of an athlete is very important when contemplating fluid needs. Sodium losses do not directly impact physical performance; however, using salts in fluid replacement is proven to enhance the thirst response and aid in rehydration (17,18,34).

Hypohydration (1% body weight loss) also decreases the ability of athletes to perform. Athletes, typically, do not replace sweat/sodium losses enough during the event. The average marathon runner will lose up to 3% body weight and if the run takes place in a temperate climate, losses could exceed up to 5%. According to Maughan, elite marathoners tend to lose salt/sweat at a rate of 2 L/h. This sweat rate exceeds intestinal absorption capability of the gut (33,19).

A plethora of studies clearly demonstrate a negative impact of hypohydration and dehydration on athletic performance (range from 1 to 8% fluid losses). Studies using sports or situations designed to mimic a sport have noted a decrement in performance for soccer, basketball, running/racing, cycling, and others (6,15–17,23). In addition, better hydration is associated with lower esophageal temperature, heart rate, and ratings of perceived exertion; all factors that, when increased, may impact performance (23).

Exercise increases the metabolic rate, and because energy is converted into heat, water losses will occur. In cold climates (winter sports or outdoor sports in mild or cold climates), heat is lost via radiation and convection, and as the temperature increases, the losses are noticeable as sweat. The physiological response to exercise is to expand the blood volume and to increase the sensitivity for sweating to occur. Athletes and their coaches, trainers, and nutritionists must be cognizant of changes in osmolarity. Body temperature and the volume of the liquid being ingested as well as the osmolarity can affect performance.

Another impact of hypohydration or dehydration that should be a concern to the athlete or their training staff is the potential for detriment on cognitive ability. The mental aspect of sports coupled with neuromuscular integration cannot be understated. The neuropsychological impacts of hydration, as well as the biological mechanisms and behavioral relationships, are relatively new areas of research. Brain behaviour and cognitive assessment is recently new to the exercise physiology field because many new cognitive assessment tools have become available.

Interesting to note, however, is a pioneer research study related to fluid and salt intake (6,15). In a review by Lieberman, hypohydration and dehydration were found to have an association with increased fatigue, impaired discrimination, impaired tracking, impaired short-term memory, and impaired recall and attention. In addition, arithmetic ability decreased while response time to peripheral visual stimuli was also affected (6,15). Cognitive applications relative to Lieberman’s study have been tested not only in academic exercise and psychology research but also with military personnel. Heat- or temperature-induced dehydration yields the same cognitive performance decrements associated with exercise-induced dehydration. This indicates that the hydration status is central for maintaining cognitive and physical performance. Cognitive performance,

under the influence of dehydration, most often results in increased fatigue and tracking errors (visual-brain connection) along with a decrease in short-term memory. Hyperhydration, on the other hand, allots an increase in short memory while having a neutral impact on the additional aforementioned factors, exclusive of any negative effects (4).

PRACTICAL MEASUREMENTS OF HYDRATION

When it comes to measuring hydration, there is no sole universal standard. There are at least 13 techniques used for assessing hydration. Water is the body’s currency because it is the medium for circulatory function, biochemical reactions, temperature regulation, and other physiological processes. In addition, fluid turnover occurs because water is lost from fluidelectrolyte shifts, in addition to losses from the lungs, skin, and kidneys. In addition, aging affects hydration needs (water is gained through the diet as well as fluid intake).

The types of hydration assessment methods (in the field and lab) include

1. stable isotope dilution
2. neutron activation analysis
3. bioelectrical impedance (BIA)
4. body mass change
5. plasma osmolality
6. plasma volume change
7. urine osmolality
8. urine specific gravity
9. urine conductivity
10. urine color
11. 24-hour urine volume
12. salivary flow rate (osmolality, flow rate, and protein content)
13. rating of thirst

An additional practical tool that is used clinically is the Hydration Assessment Checklist (HA). The HA is a lengthy in-depth assessment designed to screen for hydration problems (35). The HA is most often used in clinical conditions and in an older population. Older adults, both in the community as well as in the nursing home, are grossly underhydrated, ingesting on average less than about 0.26 gallons (1 L) daily, which is substantially lower than recommended. Of the reported halfgallon of fluid, few take in actual water as their primary fluid source. Water is an essential element supporting cellular and organ health, electrolyte balance, medication absorption and distribution, and kidney, bladder, and integumentary functioning (26,36). In essence, the importance of fluid intake for older adults is of momentous concern.

The following factors have been detailed in the literature as to why 1 gold standard for measuring hydration is not possible (1).

1. The physiological regulation of total body water volume (i.e., water turnover) and fluid concentrations is complex and dynamic. Renal, thirst, and sweat gland responses are involved to varying degrees, depending on the prevailing activities. In addition, renal regulation of water balance (i.e., arginine vasopressin) is distinct from the regulation of tonicity.

2. The 24-hour fluid deficit varies greatly among sedentary individuals and athletes primarily because of the exercise and morphology. The deficit must be matched by food and fluid intake (the fluid portion of food is often overlooked).

3. Sodium and osmolyte consumption affects the daily water requirement. Regional customs impact the ‘‘normals’’ used within biochemical assessment of hydration. For example, the mean 24-hour urine osmolality in Germany is 860 mOsm/kg, in Poland, it is 392 mOsm/kg, and in the United States, it is in the range of 280–295 mOsm/kg.

4. The volume and timing of fluid intake alters measurement of hydration. Pure water or hypotonic solutions ingested rapidly can cause dilute urine before cellular equilibrium to occur.

5. Urine samples (spot) not representing the true 24-hour void.

6. Experimental designs that differ in assessment techniques (blood versus urine).

7. Use of stable isotopes to assess hydration. However, it is not known if the isotopes are uniformly distributed throughout the body, thus the assumption used in these techniques is faulty.

8. Exercise and physical labor (as well as pregnancy labor) increase blood volume while decreasing renal blood flow and altering the glomerular filtration rate affecting hydration.

9. Changes in osmolarity and osmolality can affect the readings for hydration on certain devices (i.e., BIA).

In addition to the above, many questions exist regarding the use of plasma osmolality as a biomarker for hydration.

These include questions regarding the fact that plasma osmolality varies widely depending upon the condition being tested, environment of the test, the preexercise hydration state, and the intervention being evaluated. One question is that is there a way to meld laboratory techniques with those in the field so that trainers, coaches, and related personnel can better help athletes?

The first item to discuss is the intervention and educational sessions that athletes should receive from appropriate professionals (i.e., exercise physiologist, registered dietitian, sports nutritionist, athletic trainer, and so on). Education is the key to preventing dehydration. Combining education with accessible fluid stations (on the field or in the general area of training), available to the athletes at specific intervals, may make euhydration an easier goal to maintain

For the field technique using the combination of weighing the athlete before and after the training or competition and using the weight change as the guide for rehydration may just be the best standard when controlling for applicability, financial impact, and ease of education. The rehydration is 600 mL per 0/5 kilogram of body weight lost. Other techniques that may be able to be used in combination with monitoring weight changes include using blood and urine testing if available.

Testing for osmolality (both), sodium (both), and hematocrit levels (blood) are typical and inexpensive.

THE DIFFERENCE BETWEEN WATER AND OTHER MEANS OF REHYDRATION

Humans achieve normal hydration with a wide range of fluid intakes across their life span. Fluid homeostasis can be challenging to maintain during physical work and heat stress. Body water comprises 50–70% of body weight. Approximately 5–10% of total body water is turned over daily via obligatory losses and the need for replacement when coupled with exercise-related fluid losses becomes that much more apparent. The greater the fluid losses (from nonemergent situations, not medical or surgical), the longer the time it will take for rehydration (4% weight loss may take up to 24 hours to rehydrate), thus prevention and use of foods or fluids that may aid in more expedient rehydration is noteworthy for application (13).

Body water is maintained by matching daily water loss with intake. Metabolic water production also contributes to a small degree hydration (metabolic hydration yields approximately 250 mL/d). The Food and Nutrition Board has established an AI level of 3.7 and 2.7 L/d for men and women, respectively (11). The Continuing Survey of Food Intakes by Individuals concluded that adults receive about 25% of their daily fluid intake from foods (10). Maintaining fluid and electrolyte balance means that active individuals need to replace the water and electrolytes lost in sweat. This requires that active individuals, regardless of age, strive to hydrate well before exercise, drink fluids throughout exercise, and rehydrate once exercise is over. As outlined by the American College of Sports Medicine and the National Athletic Trainers’ Association generous amounts of fluids should be consumed 24 hours before exercise and 400–600 mL of fluid should be consumed 2 hours before exercise (this is approximately 6–10 oz) (23). During exercise, active individuals should attempt to drink approximately 150–350 mL (6–12 oz) of fluid every 15–20 minutes. If exercise is of long duration (usually .1 hour or 75 minutes) or occurs in a hot environment, sport drinks containing carbohydrate and sodium could be used.

W hen exercise is over, most active individuals have some level of dehydration. Drinking enough fluids to cover approximately 150% of the weight lost during exercise may be needed to replace fluids lost in sweat and urine. This fluid can be part of the postexercise meal, which should also contain sodium, either in the food or beverages, because diuresis occurs (fluid losses) when only plain water is ingested. Sodium helps the rehydration process by maintaining plasma osmolality and the desire to drink.

Fluid content of foods should not be underestimated or underappreciated by health professionals. High water content foods, listed as food and percent water, include iceberg lettuce (96%), cooked squash (94%), pickle (92%), cantaloupe (90%), oranges (87%), apple (86%), and pears (84%) as compared with steak (50%), cheddar cheese (37%), white bread (36%), cookies (4%), and nuts (about 2%). Therefore, including the national recommendation of 5–9 fruits and vegetables in the day also assists with hydration.

Preexercise, some athletes use beverages that contain .100 mmol/L NaCl, temporarily inducing hyperhydration, thus aiding in rehydration. Adding glycerol to the typical sports beverage or oral rehydration solution at a dose of 1.0–1.5 g/kg/body weight also assists in inducing hyperhydration (31). Nonwater sources of hydration include caffeinated beverages. Caffeine is stated to be a mild diuretic; however, the vast evidence indicates that caffeinated beverages and water hydrate to the same degree over a 24-hour period.

Fiala et al. (5) have found that caffeine is often rumored to be a mild diuretic, while noting that caffeine itself can enhance exercise performance (typical dose at 5 mg/kg). This study used 10 athletes who completed twice-a-day practices (2 h/practice = 4 h/d) for 3 consecutive days at 23_C. The study used a randomized double-blind design comparing a caffeine rehydration agent with one without caffeine (Coca-Cola versus caffeine-free version). The findings revealed that caffeine intake did not impair rehydration. No differential effects on urine or plasma osmolality, plasma volume, hematocrit, hemoglobin, or body weight were observed between the 2 groups. The caffeine (cola) intake was approximately 244 mg/d served in 7 cans/d of soda (approximately 35 mg caffeine/360 mL).

Grandjean et al. (7) found analogous results in a study of 18 males using a randomized crossover design with a free-living 24-hour capture design. The study tested 4 beverage treatments consisting of carbonated caffeine caloric cola, noncaloric caffeinated cola, and coffee and their respective effects on 24-hour hydration status. The researchers collected urine for 24 hours and analyzed for electrolytes, body weight, osmolality, emoglobin, hematocrit, blood urea nitrogen, creatinine, and other biomarkers. The results clearly denoted no differences among the groups in any variable, therefore, eliminating the connotation that caffeine be disregarded from daily fluid intake. Subsequently, the evidence supports the consumption of caffeine-containing beverages for the use of added hydration. Newer research data has started to support the inclusion of small amounts of protein with carbohydrates for hydration recovery. In 2001, 10 endurance-trained men were employed to investigate the ergogenic effects of isocaloric carbohydrate (CHO, 152.7 g) and carbohydrateprotein (CHO-PRO, 112 g CHO with 40.7 g PRO) drinks ingested after a glycogen-lowering diet and exercise bout. Treatments were administered in a double-blind and counterbalanced fashion. After a glycogen-lowering diet and run, 2 dosages of a drink were administered with a 60-minute interval between dosages. The CHO-PRO trial resulted in higher serum insulin levels (60.84 versus 30.1 mU/mL) 90 minutes into recovery than the CHO-only trail (p , 0.05). Furthermore, the time to run to exhaustion was longer during the CHO-PRO trial (540.7 6 91.56 seconds) than the CHO-only trial (446.1 6 97.09 seconds; p , 0.05). In conclusion, a CHO-PRO drink after glycogen-depleting exercise may facilitate a greater rate of muscle glycogen resynthesis than a CHO-only beverage, hasten the recovery process, and improve exercise endurance during a second bout of exercise performed on the same day (24). Subsequent studies have found that adding protein in the ratio of 1 part protein to every 4 parts carbohydrate has been found to induce exercise hydration on the magnitude of 15% better than the typical carbohydrate beverage and 40% more than water alone (12,27).

A study by Seifert et al. (27) actually concluded, ‘‘contrary to popular misconception, adding protein to a carbohydrate-based sports drink led to improved water retention by 15% over [a carbohydrate-only sports drink] and 40% over plain water.’’ In the study, cyclists exercised until they lost 2% of their body weight (through sweating) and then drank a carbohydrate-protein sports drink (Accelerade), a carbohydrate only sports drink (Gatorade), or water. Over the next 3 hours, measurements were taken to determine how much of each beverage was retained in the body (versus the amount lost through urination). The carbohydrate-protein sports drink was found to rehydrate the athletes 15% better than the carbohydrate only sports drink and 40% better than water. All 3 drinks emptied from the stomach and were absorbed through the intestine at the same rate. In addition, there was no difference between the carbohydrate-protein drink and the carbohydrate-only drink regarding the effects on blood plasma volume. This suggests that the carbohydrate-protein drink resulted in increased water retention within and between cells. Therefore, when rehydration and fluid retention are of concern; a carbohydrate-protein sports drink may be preferable over plain water and a carbohydrate-electrolyte sports drink.

An additional sports application study by Seifert et al. (28) found that ‘‘ingestion of a carbohydrate-protein beverage minimized muscle damage indices during skiing compared with placebo and no fluid.’’ Thirty-one recreational skiers were separated into 3 groups. All 3 groups skied 12 runs, which took about 3 hours. One group drank nothing. A second group drank 6 oz (.18 L) of a placebo (flavored water) after every second run. A third group drank an equal amount of the carbohydrate- protein sports drink (Accelerade).

After the 12th run, blood samples were taken from each skier and analyzed for 2 biomarkers of muscle stress (myoglobin and creatine kinase). Subjects who received the carbohydrateprotein sports drink showed no signs of muscle damage, while indicators of muscle damage increased by 49% in subjects receiving only water. Thus, it is reasonable to conclude that in this type of sport using a carbohydrate-protein drink is more beneficial than water for maintaining skeletal integrity and hydration. Typically hydration and rehydration for athletes is done with a 6–8% glucose-electrolyte solution. Newer research is finding that adding just a small amount of protein to this type of sports beverage not only enhances hydration and rehydration (or hydration maintenance) but also promotes muscle protein synthesis (which does not happen with CHO alone) and glycogen reaccumulation while reducing markers of muscle damage. These beverages are gaining popularity for their multiple benefits that seem to make them superior to the typical sports beverage during exercise or postexercise nutrition.

FLUID REPLACEMENT

Fluid replacement is a vital component and must be addressed in a diligent manner. In general, sports nutritionists use the following fluid recommendations (25,20):j 480–600 cc fluid: 1–2 hours before Exercise 300–480 cc fluid: 15 minutes before exercise 120–180 cc fluid: every 10–15 minutes during exercise In general, start fluid intake 24 hours before exercise event. Fluid intake coming from food must also be considered. As aforementioned, however, hydration in the postexercise recovery is best achieved by the ingestion of either the typical glucoseelectrolyte solution or a carbohydrateprotein mixture. However, if the exercise has duration of less than 60–75 minutes, then plain water (may be flavored) is recommended. There are no proven ergogenic effects or benefits from vitamin- or mineral-enriched waters except that they provide absorbable nutrients at lower caloric costs than some foods. Despite the lack of ergogenic enhancement, research shows that the volume of fluid intake generally increases when water or the beverage is flavored (22). The athlete may consider taking note of the volume of his/her beverage intake to become more familiar with how their body responds to rehydration. The athlete can personalize his/her fluid intake based upon what

types of beverages result in improved recovery as measured by hydration, return to normal body weight, subsequent exercise performance, and effects on mental abilities/cognition.

CONCLUSION

Exercise increases the metabolic rate. Energy production leads to heat loss, and fluid status is affected. The climate has an underappreciated effect on hydration status. In cold climates, the thermoregulatory response includes enhanced heat production by a variety of means; all resulting in increased fluid losses. Exercising in temperate climates is actually a little easier because the body’s accommodation response is to increase blood volume and sweating mechanism sensitivity. Athletes, along with their trainers and coaches, must be cognizant about the physiological impacts of exercise, such as changes in body temperature and blood volume, in their surrounding climate. Elevated temperature is related to blood volume reduction and performance.

Maintaining fluid balance reduces the effects of climate and/or blood volume on hydration status. For exercise lasting less than an hour, water or noncaloric fluid is recommended. It is not well known if ‘‘nonintensive’’ exercise requires that the rehydration solution include carbohydrate and electrolytes.

Most data note no need for supplemented calories and salts with shortterm exercise bouts. If the exercise is longer in duration, maintaining hydration and rehydration is much more important. Beverages beneficial for enhancing rehydration include carbohydrate- electrolyte solutions and carbohydrate- protein beverages (C-P).

Caffeinated beverages, with and without calories, also add to hydration and rehydration. Although in the immediate postexercise period, data are mounting for C-P to be the superior postexercise rehydration and recovery beverage.

Future research will focus on the multiple applications of this admixture beverage along with other potential beneficial effects. Taste acceptance is very important for any of these beverages to actually be used by athletes; therefore, overcoming taste issues for beverages that contain protein remains an issue for researchers and food scientists to overcome. In conclusion, maintaining euhydration and understanding how to rehydrate after exercise is an important aspect of sports nutrition that is underdiscussed and/or underappreciated.

Douglas S. Kalman is a director in the Nutrition and Endocrinology Division of Miami Research Associates and is also an adjunct professor of Sports Nutrition and Advanced Metabolism in the Robert Stempel School of Public Health at Florida International University.

Anna Lepeley is a doctoral candidate for Touro University and a cohost on the Strength-Power Hour Radio Show.

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14. Leibowitz SF. Hypothalamic alpha- and beta- adrenergic systems regulate both thirst and hunger in the rat. Proc Natl Acad Sci U S A 68: 332–334, 1971.

15. Lieberman HR. Hydration and cognition: A critical review and recommendations for future research. J Am Coll Nutr 26: 555s– 561s, 2006.

16. Manz F. Hydration and disease. J Am Coll Nutr 26: 535s–541s, 2007.

17. Maughan RJ. Fluid and electrolyte loss and replacement in exercise. J Sports Sci 9: 117, 1991.

18. Maughan RJ, Leiper JB, and Sherriffs SM. Restoration of fluid balance after exerciseinduced dehydration: Effect of food and fluid intake. Int J Appl Physiol 73: 317, 1996.

19. Maughan RJ and Lieper JB. Sodium intake and post-exercise rehydration in man. Eur J Appl Physiol 71: 311, 1995.

20. McArdle WD, Katch FI, and Katch VL. Sports and Exercise Nutrition. Philadelphia: Lippincott Williams & Wilkins, 1999. pp. 275–276.

21. McKinley MJ and Johnson, AK. The physiological regulation of thirst and fluid intake. News Physiol Sci 19: 1–6, 2004.

22. Minehan MR, Riley MD, and Burke LM. Effect of flavor and awareness of kilojoule content of drinks on preference and fluid balance in team sports. Int J Sports Nutr Exerc Metab 12: 81–92, 2002.

23. Murray B. Hydration and physical performance. J Am Coll Nutr 26: 542s– 548s, 2006.

24. Niles ES, Lachowetz T, and Garfi J. Carbohydrate-protein drink improves time to exhaustion after recovery from endurance exercise. J Exerc Physiol 4: 45–52, 2001.

25. Pivarnik JM. Water and electrolytes during exercise In: Nutrition in Exercise and Sports. Wolinsky I, ed. Boca Raton, FL: CRC Press, 1989. pp. 185–200.

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27. Seifert JG, Harmon J, and DeClercq P. Protein added to a sports drink improves fluid retention. Int J Sports Nutr Exerc Metab 16: 420–429, 2006.

28. Seifert JG, Kipp RW, Amann M, and Gazal O. Muscle damage, fluid ingestion, and energy supplementation during recreational alpine skiing. Int J Sports Nutr Exerc Metab 15: 528–536, 2005.

29. Senay LC. Water and electrolytes during physical activity. In: Nutrition in Exercise and Sport (3rd ed), Wolinsky I, ed. Boca Raton, FL: CRC press, 1998. pp 258–273.

30. Sharp RL. Role of sodium in fluid homeostasis with exercise. J Am Coll Nutr 25: 231s–239s, 2006.

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34. Wilk B and Bar-Or O. Effect of drink flavour and NaCl on voluntary drinking and hydration in boys exercising in the heat. J Appl Physiol 80: 1112, 1996.

35. Zembrzuski CD. Hydration assessment checklist. Geriatr Nurs 18: 20–26, 1997.

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Thursday
Dec292011

Flight Nutrition Guidelines

Gary Slater/ Michelle Cort Sports Dietitians Australian Institute of Sport

Website: Australian Rowing website


Nutrition and Hydration Strategies for Long Haul Flights

To reduce the interference that long haul flights can have on performance the first few days after arrival, it is important to ensure you have appropriate nutrition and hydration strategies in place before, during and immediately after the flight.

Meals and Snacks:

• In addition to adjusting your sleep patterns to coincide with those of your destination in the days prior to departure, try to adopt the meal pattern you will have at your destination. This will help reduce jet lag and adjust your body clock.
• Rowers with reduced energy needs (e.g. those attempting to make weight or on ‘low energy budgets’) may not need all the meals and snacks provided during flights. Drinking low energy fluids (water, tea, diet soft drinks) and chewing sugar free gum can decrease the temptation to snack excessively during flights. Alternatively pack your own lower energy snacks like fresh fruit and decline some of the high energy/ high fat in-flight snacks.
• Rowers with high fuel needs should pack extra snacks to supplement the food provided in-flight to ensure weight loss and a decrease in fuel stores does not occur. Good snack choices include cereal bars, sports bars, powdered liquid meal supplements (plus a shaker), plus dried fruit and nut mixes.

Hydration Strategies:

• The risk of becoming dehydrated on long flights is increased as the pressurised cabin and air-conditioned environment increases fluid losses from the skin and lungs. The small fluid serve sizes available on flights are usually insufficient to maintain hydration.
• Purchase extra fluids after clearing security to add to your carry on luggage.
• Aim for approximately 1 cup per hour to maintain hydration.
• Suitable choices include: water, sports drink, juice, soft drink, tea and coffee.
• Sodium assists in decreasing urine losses (and thus promoting improved hydration). Sports drinks contain a small amount of sodium that can be useful. Other electrolyte rich solutions (e.g. Gastrolyte in water or Gatorlytes added a sports drink) can also be valuable, especially for those who struggle to remain well hydrated.
• Once at your destination rapid re-hydration should be a priority. Continue to drink regularly. Adding Gastrolyte to water (10 tablets or 5 sachets in 1L of water) on arrival can help promote faster re-hydration.

New Rules for International Flights:

To enhance flight safety the federal government has enforced new rules about taking liquids, aerosols and gels on flights into and out of Australia. In brief, each container of liquid, aerosols or gels in carry-on luggage AT THE SECURITY SCREENING POINT (but not when you board the plane) must be less than 100 ml.

By following the guidelines below, this should have no impact on your in-flight hydration strategies.

• Carry an empty drink bottle through the security screening point, filling your drink bottle up at a bubbler on the other side of the screening point.
• Purchase drinks (including water, sports drinks, juices, etc) at shops on transit to your departure gate.
• Include powdered sports drinks, powdered liquid meal supplements (e.g. Power Bar Protein Plus, Sustagen Sport) and perhaps sachets/tablets of oral rehydration salts (Gastrolyte, Gatorlytes) in your carry on luggage that can be made up (on water) in your drink bottle or shaker for the flight.

For more information on these new travel regulations, check out the Australian Government Department of

Transport and Regional Services information sheet at: 

Australia - page 2.

Great Britain and Europe

USA

Sunday
Dec182011

Nutrition Strategies for Rowing

Written by the Department of Sports Nutrition, AIS 2006
Australian Sports Commission 2006

For a print copy: Nutrition Strategies for Rowing


Training Nutrition:

Rowing requires a unique mix of technique, power and endurance, utilising both the anaerobic and aerobic energy systems. Rowers have very high energy and carbohydrate requirements to support training loads and meet body weight and strength goals.

Some rowers (particularly male heavyweights) struggle with the shear volume of food they need to consume to meet their training demands. Frequent snacks and the use of compact, energy dense food or drinks such as juice, flavoured milk, jam, honey, sports bars and liquid meals are necessary to keep the volume of food manageable.

Nutrition recovery strategies between sessions are extremely important and the rower must have a planned approach to their training nutrition.

Carbohydrate: How much?

Carbohydrate is a critical fuel source for the muscle and central nervous system. Carbohydrate intake before, during and after exercise can be required to meet the fuel requirements of the activity.

A rower can calculate a carbohydrate target in grams, and use food tables or information on food labels to plan to meet this goal. Even better, a rower can see a Sports Dietitian for advice to further narrow this target range according to his/her specific situation, and have an individualised meal plan fitted to their needs.

Situation

Recommended Carbohydrate Intake

Daily refuelling needs for training programs less than 60-90mins per day or low intensity exercise

Daily intake of 5-7g per kg body mass.

Daily refuelling for training programs greater than 90-120 min per day

Daily intake of 7-10g per kg body mass.

Daily refuelling for athletes undertaking extreme exercise program: 6-8 hours per day

Daily intake of 10-12+ g per kg body mass.

Pre-event meal

Meal eaten 1-4 hrs pre-competition 1-4g per kg body mass.

Carbohydrate intake during training sessions and competition events greater than 1 hour

1g per minute, or 60g per hour

Rapid Recovery after training session or multi event competition, especially when there is less than 8 hrs until the next session

Intake of 1g per kg body mass in the first 30 min after exercise, repeated every 1-2 hrs until regular meal patterns are resumed

 

A chart that provides information about the carbohydrate content of common foods can be viewed on (www.ais.org.au/nutrition). You can use this information to plan a daily menu, or specific pre-competition meals and post exercise snacks and meals.

Protein:

Rowers in heavy training require extra protein to cover a small proportion of their energy costs of their training and to assist in the repair and recovery process after exercise. Adolescent rower’s who are still growing, have additional protein requirements.

Protein Requirements can be summarised as follows:

Situation

Grams protein per kg body mass per day

Light training program

1.0

Moderate to heavy training

1.2-1.7

Adolescent Rowers

2.0

 

Which foods are the best to provide protein?

The following table indicates the protein content of many foods. Each of the foods provides approximately 10g of protein.

Animal Foods

Plant Foods

2 small eggs

30g (1.5 slices) reduced fat cheese

70g cottage cheese

1 cup (250ml) low fat milk

35g lean beef, lamb or pork (cooked weight)

40g chicken (cooked weight)

50g grilled fish

50g canned tuna or salmon

200g reduced fat yoghurt

150g light fromage frais

4 slices (120g) bread

3 cups (90g) wholegrain cereal

2 cups (330g) cooked pasta

3 cups (400g) cooked rice

¾ cup (150g) lentils or kidney beans

200g baked beans

120g tofu

400ml soy beverage

60g nuts or seeds

1 cup (250ml) soy milk

100g soy ‘meat’

 

Are high protein low carbohydrate diets appropriate for Rowers?

In the short term high protein, low carbohydrate diets result in loss of water and glycogen. This might result in a decrease on the scales, but does nothing to reduce body fat. In the long term high protein, low carbohydrate diets may result in fat loss. The effect is primarily due to the fact that these diets are low in kilojoules rather than any magical effect from the protein itself. The lack of carbohydrate reduces energy levels, impairs performance and causes lethargy and nausea. High protein, low carbohydrate diets restrict the intake of many nutrients in the diet. These diets will result in muscle mass decrease. High protein, low carbohydrate diets are not suitable for athletes.

Weight Loss:

In lightweight rowing the need to maintain low levels of body fat is important. Rowers needing to reduce skinfolds must target excess kilojoules in their diet. In particular, excess fat, alcohol and sugary foods should be targeted and replaced with more nutrient dense choices (see the AIS Sports Nutrition Fact Sheet: “Weight Loss” www.ais.org/nutrition for more detailed information)

Muscle Mass Gain:

Specific information relating to nutrition strategies for lean muscle mass gain can be found in the AIS Sports Nutrition Fact Sheet: “How to Grow Muscles” (www.ais.org.au/nutrition).

Pre Exercise Nutrition:

Depletion of carbohydrate stores is a major cause of fatigue during exercise.

Eating Before Early Morning Sessions:

After an overnight fast (sleeping) liver glycogen (energy) stores are substantially depleted. Therefore, pre training carbohydrate intake is important for maintaining blood glucose levels towards the end of prolonged training sessions.

Example: some fruit and a cereal bar on the way to training along with some fluid such as a sports drink would be a good choice. If tolerating solid food before training is difficult a liquid meal alternative such as Protein Plus drink or a smoothie or even a glass of juice can be useful in providing essential carbohydrate.

Making up for the smaller carbohydrate intake before exercise by consuming carbohydrate during the training session (eg: sports drink) is an important strategy. The rower should experiment to find a routine that works and is comfortable for them.

Other Exercise Sessions:

Food eaten before training should contain carbohydrate. It should also be low in fat and fibre to aid in digestion and reduce the risk of gastrointestinal discomfort or upsets.  Fluid needs should also be considered.

Further detailed information on pre exercise eating can be accessed on www.ais.org.au/nutrition in the AIS “Eating Before Exercise” fact sheet.

Recovery Nutrition Strategies:

Recovery is a challenge for rowers who are undertaking two or more sessions each day, training for long periods, or competing in a program that involves multiple races. Between each workout the body has to adapt to the physiological stress. In training, with correct planning of the workload and the recovery time, adaptation allows the body to become fitter, stronger and faster. In competition however, there may be less control over the work to recovery ratio.

Nutrition recovery strategies encompass a complex range of processes that include:
• restoring the muscles and liver with expended fuel (glycogen)
• replacing the fluid and electrolytes lost in sweat
• allowing the immune system to handle the damage and challenges caused by the exercise bout.
• Manufacturing new muscle protein, red blood cells and other cellular components as part of repair and adaptation processes

The importance of each of these goals varies according to the workout. A pro-active recovery means providing the body with all the nutrients it needs, in a speedy and practical manner, to optimise the desired processes following each session.

Refuelling:
To kick start the refuelling process an intake of at least 1g/kg of carbohydrate (50-100g) for most athletes is needed. Athletes should consume this carbohydrate -in their next meal or snack- as soon as possible after a heavy session to prepare for the next.

Rehydration:
Most athletes finish a training or competition session with some level of fluid deficit. Comparing pre and post exercise measurements of  body weight can provide an approximation of the overall fluid deficit. Athletes may need to replace 150% of the fluid deficit to get back to baseline.

Immune System:
The immune system is suppressed by intensive training. This may place athletes at risk of succumbing to an infectious illness during this time. Consuming carbohydrate during and/or after a prolonged or high intensity work out has been shown to reduce the disturbance to immune system markers.

Muscle Repair and Building:
Prolonged and high intensity exercise causes a substantial breakdown of muscle protein. During the recovery phase there is a reduction in catabolic (breakdown) processes and a gradual increase in anabolic (building processes). Early intake of good quality protein foods helps to promote the increase in protein rebuilding. Protein consumed immediately after the session (or in the case of resistance training sessions, immediately before the session), is taken up more effectively by the muscle into rebuilding processes, than protein consumed in the hours afterwards.

However the protein needs to be consumed with carbohydrate foods to maximise this effect. Carbohydrate intake stimulates an insulin response, which potentiates the increase in protein uptake and rebuilding.

Nutritious Carbohydrate – Protein Recovery Snacks (contain 50g carbohydrate + valuable source of protein):

- 250-300ml liquid meal supplement (eg: Protein Plus Drink)
- 250-300ml milkshake or fruit smoothie
- 1-2 sports bars (check labels for carbohydrate and protein content)
- 1 large bowl (2 cups) breakfast cereal with milk
- 1 large or 2 small cereal bars + 200g fruit flavoured yoghurt
- 1 bread roll with cheese/meat filling + banana
- 300g (bowl) fruit salad with 200g fruit flavoured yoghurt
- 2 x crumpets with peanut butter and 200ml falvoured milk

Hydration Strategies:

Drinking regularly during exercise, athletes can prevent the negative effects associated with dehydration and performance can be improved. Every rower should make fluid replacement a key priority during training and competition. Long training sessions on the water lead to significant sweat losses.

The table below shows sweat losses and fluid intakes recorded on AIS rowers in different environmental conditions. Despite having drink bottles available, athletes failed to consume enough fluid to keep up with their sweat losses, particularly in hot weather. Note however, that even in cold weather considerable sweat losses were seen.

Session

Season

Sweat losses men

(ml/hr) (range)

Fluid intake men

(mlhr) (range)

Sweat losses women (ml/hr) (range)

Fluid intake, women (mlhr) (range)

Training

Hot conditions 320C

1980

(990-2150)

960

(410-1490)

1390

(740-2335)

780

(290-1390)

Training

Cool conditions 100C

1165

(430-2000)

582

(215-1265)

780 (360-1550)

405

(145-660)

 

Dehydration impairs the body’s ability to regulate heat resulting in increased body temperature and an elevated heart rate. Associated negative effects include: increased perceived exertion, reduced mental function (decreased motor control, decision making and concentration). Gastric emptying is also slowed, resulting in stomach discomfort. All of these effects lead to an impairment in exercise performance. The negative effects of dehydration on performance are exacerbated further in hot conditions.

Fluid requirements vary markedly between rowers and in different exercise sessions. It is impossible to prescribe a general fluid replacement plan that will meet the needs of all rowers. Rowers can estimate their own fluid requirements by weighing themselves pre and post exercise sessions. Each kilogram lost is approximately equivalent to 1 litre of fluid. Once a rower’s individual sweat losses are known, a plan can be prepared to help him/her to achieve better fluid replacement in following exercise sessions.

Where possible it is better to begin drinking early in exercise and adopt a pattern of drinking small volumes regularly rather than trying to tolerate larger volumes in one hit.

What to Drink?
Research shows that fluid intake is enhanced when beverages are cool (~ 150C), flavoured and contain sodium. This makes sports drinks an ideal choice during exercise. In addition to replacing fluid and electrolytes lost through sweat, sports drink also contains carbohydrate which allows re-fuelling to take place during exercise.

Water is still a suitable option during exercise. However water drinkers need to be aware that water does not stimulate fluid intake to the same extent as sports drinks. Drinking to a plan is therefore crucial when drinking water. Don’t rely on thirst.

Cordial, soft drinks and juice generally contain greater than 10% carbohydrate and are low in sodium. This can slow gastric emptying and makes these drinks a less suitable choice, especially for high intensity activity.

Other Useful Hydration Strategies:

• Drink with all meals and snacks. Consume 300-400ml of fluid in the hour before training commences to ensure you begin each session hydrated.
• Take sufficient drink bottles to training. Keep some in the coaches boat for top ups.
• Take a few seconds every 15-20mins or between pieces for a drink break. Alternatively, try using a drink container like a hydration-pack, which is worn on the back, to avoid having to take your hands off the oar to drink.
• Re-hydrate fully after the session.
• Sports drinks are the recommended fluid choice during rowing.
• Lightweight rowers should not consider a lower weight at the end of a workout to be a good sign. Even though dehydration is an inevitable part of making weight for competition, it is counterproductive and unnecessary in the training setting.

Competition Nutrition:

Rowers should go into each race with fluid and fuel stores topped up, and feeling comfortable after their last meal. With the regatta or competition lasting a number of days, the challenge is to recover between each day’s sessions and to prepare for the next race (see Recovery Nutrition Strategies section above).

Generally a meal that provides carbohydrate should be consumed 2-3 hours before a race, eg: breakfast cereal, toast, muffins, sandwiches, yoghurt, fruit, pasta and creamed rice. Some rowers need to take special care with pre race eating, as it can be very uncomfortable to race with a full stomach. Low bulk choices such as liquid meals and sports bars can be useful in these situations.

Rowers need to organise themselves to have appropriate food and fluids available at all times during competition. Many athletes find that they easily lose weight over the course of a competition due to being unable to consume their usual high energy diet (as they are spending much of the day in preparation and the race itself) To help avoid this from happening take along a supply of cereal bars, liquid meal supplements sports bars, fruit bars, dried fruit, sandwiches, yoghurt, juice etc…

Be aware of your fluid needs (see Hydration Strategies section above). You can be dehydrated from your rowing efforts, making weight practices or just from sitting in the sum watching competition.

Supplements:

While a lot of sports foods and supplements do not live up to their emotive claims, some of these products are valuable in helping an athlete achieve their nutritional goals and optimal performance. State of the art information on Sports Foods and Supplements can be found in the AIS Sports Supplement Program information and the AIS “Supplements in Sport – Why are they so tempting?” fact sheet, which are both located at: www.ais.org.au/nutrition.

Some sports foods and dietary supplements play a role in providing a practical alternative to food (eg: sports drinks, sports gels, sports bars, and liquid meal supplements). Rowers may find these products valuable in helping them achieve their nutrition goals in a busy day or during an exercise session. They are an alternative to every day foods, which might need to be combined and juggled to produce the same nutritional composition, or which might be too impractical to consume directly before or during intense exercise. Sometimes the convenience factor is the selling point.

Some rowers however use these products outside the conditions in which they are likely to achieve a direct sport nutrition goal (eg: eating sports bars as a snack). In these situations sports foods may simply be a more expensive version of food. Over-consumption of any sports foods can lead to dietary imbalances as well as being an unnecessary burden on the wallet. Specific sports nutrition advice from a Sports Dietitian will make the rower aware of the best uses of these special sports foods.

Sports Dietitians:

While this information provides a good general overview to sports nutrition for rowing, a more individualised nutrition plan will help to maximise your rowing performance. Your State Institute or Academy will have the expertise to help you. Additionally Sports Dietitians Australia (http://www.sportsdietitians.com.au/) has a list of accredited Sports Dietitians throughout Australia that can provide you with this service.

 

 

Sunday
Oct232011

Recovery nutrition?

Written by the AIS Sports Nutrition, last updated July 2009. © Australian Sports Commission

Website link: Australian Rowing


What are the priorities for recovery nutrition?

Recovery is a challenge for athletes who are undertaking two or more sessions each day, training for prolonged periods, or competing in a program that involves multiple events. Between each work-out, the body needs to adapt to the physiological stress. In the training situation, with correct planning of the workload and the recovery time, adaptation allows the body to become fitter, stronger and faster. In the competition scenario, however, there may be less control over the work-to-recovery ratio. A simpler but more realistic goal may be to start all events in the best shape possible.

Recovery encompasses a complex range of processes that include;
 • refueling the muscle and liver glycogen (carbohydrate) stores
 • replacing the fluid and electrolytes lost in sweat
 • manufacturing new muscle protein, red blood cells and other cellular components as part of the repair and adaptation process
 • allowing the immune system to handle the damage and challenges caused by the exercise bout

The emphasis an athlete needs to place on each of these broad goals will vary according to the demands of the exercise session.  Key questions that need to be answered include - How much fuel was utilised?  What was the extent of muscle damage and sweat losses incurred?  Was a stimulus presented to increase muscle protein?

A proactive recovery means providing the body with all the nutrients it needs, in a speedy and practical manner, to optimise the desired processes following each session.  State-of-the-art guidelines for each of the following issues are presented below.

Refueling

Muscle glycogen is the main fuel used by the body during moderate and high intensity exercise. Inability to adequately replace glycogen stores used up during a workout will compromise performance in subsequent sessions.

The major dietary factor in postexercise refueling is the amount of carbohydrate consumed. Depending on the fuel cost of the training schedule or the need to fuel up to race, a serious athlete may need to consume between 7-12 g of carbohydrate per kg body weight each day (350-840 g per day for a 70kg athlete) to ensure adequate glycogen stores. As an overemphasis on other nutrients, such as protein and fat, can easily replace carbohydrate foods within the athlete’s energy requirements, careful planning of meals and snacks throughout the day is needed achieve the required level of intake (for more information on carbohydrate requirements for athletes, refer to the “Carbohydrate”  Fact Sheet). 

In the immediate post exercise period, athletes are encouraged to consume a carbohydrate rich snack or meal that provides 1-1.2 g of carbohydrate per kg body weight within the first hour of finishing, as this is when rates of glycogen synthesis are greatest. This is especially important if the time between prolonged training sessions is less than 8 hrs. The type and form (meal or snack) of carbohydrate that is suitable will depend on a number of factors, including the athletes overall daily carbohydrate and energy requirements, gastric tolerance, access and availability of suitable food options and the length of time before the next training session. Table 1 gives examples snacks providing at least 50g of carbohydrate.

Rehydration

The majority of athletes will finish training or competition sessions with some level of fluid deficit.  Research suggests that many athletes fail to adequately drink sufficient volumes of fluid to restore fluid balance. As a fluid deficit incurred during one session has the potential to negatively impact on performance during subsequent training sessions, athletes need to incorporate strategies to restore fluid balance, especially in situations where there is a limited amount of time before their next training session.

Athletes should aim to consume 125-150% of their estimated fluid losses in the 4-6 hours after exercise (Refer to the “How much do athletes sweat?” Fact Sheet for advice on how to monitor fluid losses during exercise). The recommendation to consume a volume of fluid greater than that lost in sweat takes into account the continued loss of fluid from the body through sweating and obligatory urine losses.

Fluid replacement alone will not guarantee re-hydration after exercise. Unless there is simultaneous replacement of electrolytes lost in sweat, especially sodium, consumption of a large volume of fluid may simply result in large urine losses. The addition of sodium, either in the drink or the food consumed with the fluid, will reduce urine losses and thereby enhance fluid balance in the post exercise period.  Further, sodium will also preserve thirst, enhancing voluntary intake. As the amount of sodium considered optimal for re-hydration (50-80 mmol/L) is in excess of that found in most commercially available sports drinks, athletes may be best advised to consume fluids after exercise with everyday foods containing sodium.

In considering the type of fluids needed to achieve their re-hydration goals, athletes should also consider the length of time before their next session, the degree of the fluid deficit incurred, taste preferences, daily energy budget, as well as their other recovery goals. With the latter, athletes can simultaneously meet their refueling, repair and contribute to their re-hydration goals by consuming fluids that also provide a source of carbohydrate and protein e.g. flavoured milk, liquid meal supplement.

Muscle Repair and Building

Prolonged and high-intensity exercise causes a substantial breakdown of muscle protein. During the recovery phase there is a reduction in catabolic (breakdown) processes and a gradual increase in anabolic (building) processes, which continues for at least 24 hours after exercise. Recent research has shown that early intake after exercise (within the first hour) of essential amino acids from good quality protein foods helps to promote the increase in protein rebuilding. Consuming food sources of protein in meals and snacks after this “window of opportunity” will further promote protein synthesis, though rate at which it occurs is less.

Though research is continuing into the optimal type (e.g. casein Vs whey), timing and amount of protein needed to maximise the desired adaptation from the training stimulus, most agree that both resistance and endurance athletes will benefit from consuming 15-25g of high quality protein in the first hour after exercise. Adding a source of carbohydrate to this post exercise snack will further enhance the training adaptation by reducing the degree of muscle protein breakdown.  Table 2 provides a list of carbohydrate rich snacks that also provide at least 10g of protein, while Table 3 lists a number of everyday foods that provide ~10g of protein.

Immune System

In general, the immune system is suppressed by intensive training, with many parameters being reduced or disturbed during the hours following a work-out.  This may place athletes at risk of succumbing to an infectious illness during this time. Many nutrients or dietary factors have been proposed as an aid to the immune system - for example, vitamins C and E, glutamine, zinc and most recently probiotics - but none of these have proved to provide universal protection.  The most recent evidence points to carbohydrate as one of the most promising nutritional immune protectors.  Ensuring adequate carbohydrate stores before exercise and consuming carbohydrate during and/or after a prolonged or high-intensity work-out has been shown to reduce the disturbance to immune system markers.  The carbohydrate reduces the stress hormone response to exercise, thus minimising its effect on the immune system, as well as also supplying glucose to fuel the activity of many of the immune system white cells.

How does recovery eating fit into the big picture of nutrition goals?

To optimise recovery from a training session, meals (which generally supply all the nutrients needed for recovery) must either be timetabled so that they can be eaten straight after the work-out, or special recovery snacks must be slotted in to cover nutrient needs until the next meal can be eaten.

For athletes who have high-energy needs, these snacks make a useful contribution towards their daily kilojoule requirement.  When there is a large energy budget to play with, it may not matter too much if the snacks only look after the key recovery nutrients - for example carbohydrate e.g. sports drink.  On the other hand, for those athletes with a low energy budget, recovery snacks will also need to contribute towards meeting daily requirement for vitamins, minerals and other nutrients.  Snacks that can supply special needs for calcium, iron or other nutrients may double up as suitable recovery snacks. e.g. yoghurt

Real food Vs supplements

Many athletes fall into the trap of becoming reliant on sports food supplements, believing this to be the only and/or best way to meet their recovery goals. This often results in athletes “doubling up” with their recovery, consuming a sports food supplement that meets certain recovery goals e.g. liquid meal supplement, then following this up soon afterwards with a meal that would help them meet the same recovery goal e.g. bowl of cereal with fresh fruit.  Unless constrained by poor availability or lack of time, athletes are best advised to favour real food/fluid options that allow them to meet recovery and other dietary goals simultaneously. This is especially important for athletes on a low energy budget.

What are some other the practical considerations for recovery eating?

Some athletes finish sessions with a good appetite, so most foods are appealing to eat. On the other hand, a fatigued athlete may only feel like eating something that is compact and easy to chew. When snacks need to be kept or eaten at the training venue itself, foods and drinks that require minimal storage and preparation are useful. At other times, valuable features of recovery foods include being portable and able to travel interstate or overseas. Situations and challenges in sport change from day to day, and between athletes - so recovery snacks need to be carefully chosen to meet these needs.

Table 1- Carbohydrate-rich recovery snacks (50g CHO portions)
 • 700-800ml sports drink
 • 2 sports gels
 • 500ml fruit juice or soft drink
 • 300ml carbohydrate loader drink
 • 2 slices toast/bread with jam or honey or banana topping
 • 2 cereal bars
 • 1 cup thick vegetable soup + large bread roll
 • 115g (1 large or 2 small) cake style muffins, fruit buns or scones
 • 300g (large) baked potato with salsa filling
 • 100g pancakes (2 stack) + 30g syrup

Table 2- Nutritious carbohydrate-protein recovery snacks (contain 50g CHO + valuable source of protein and micronutrients)
 • 250-300ml liquid meal supplement
 • 300g creamed rice
 • 250-300ml milk shake or fruit smoothie
 • 600ml low fat flavoured milk
 • 1-2 sports bars (check labels for carbohydrate and protein content)
 • 1 large bowl (2 cups) breakfast cereal with milk
 • 1 large or 2 small cereal bars + 200g carton fruit-flavoured yoghurt
 • 220g baked beans on 2 slices of toast
 • 1 bread roll with cheese/meat filling + large banana
 • 300g (bowl) fruit salad with 200g fruit-flavoured yoghurt
 • 2 crumpets with thick spread peanut butter + 250ml glass of milk
 • 300g (large) baked potato + cottage cheese filling + glass of milk

Table 3 - Foods providing approximately 10g of protein.

Animal foods
 • 40g of cooked lean beef/pork/lamb
 • 40g skinless cooked chicken
 • 50g of canned tuna/salmon or cooked fish
 • 300 ml of milk/glass of Milo
 • 200g tub of yoghurt
 • 300ml flavoured milk
 • 1.5 slices (30g) of cheese
 • 2 eggs

Plant based foods
 • 120g of tofu
 • 4 slices of bread
 • 200g of baked beans
 • 60g of nuts
 • 2 cups of pasta/3 cups of rice
 • .75 cup cooked lentils/kidney beans

 


Friday
Oct072011

Basic Principles for Improving Sports Performance 

By David R. Lamb, Ph.D. Exercise Physiology Laboratory, Sport and Exercise Science Faculty, The Ohio State University, Columbus, OH , Chairman,
Gatorade Sports Science Institute. Print copy: Basic Principles for Improving Sports Performance


Key points

1. For most sports, the top competitor is generally the one who can appropriately sustain the greatest power output to overcome resistance or drag.
2. It is not sufficient for championship performance to simply have the ability to produce great power. The champion must be able to sustain power output in an efficient and skillful manner for the duration of the competition.
3. During maximal exercise lasting a few seconds, the anaerobic breakdown of phosphocreatine and glycogen in muscles can provide energy at rates many times greater than can be supplied by the aerobic breakdown of carbohydrate and fat. However, this high rate of anaerobic energy production cannot be sustained for more than about 20 seconds.
4. For exercise lasting more than a few minutes, an athlete who has a high lactate threshold, that is, one who can produce a large amount of energy aerobically without a major accumulation of lactic acid in the blood, will be better able to sustain a higher rate of energy expenditure than will a competitor who has a lower lactate threshold.
5. A high level of mechanical efficiency, which is the ratio of the mechanical power output to the total energy expended to produce that power, is vital if an athlete is to make the most of his or her sustainable rate of energy expenditure. Mechanical efficiency depends upon the extent to which the athlete can recruit slow-twitch muscle fibers, which are more efficient at converting chemical energy into muscle contraction than are fast-twitch fibers.
6. Neuromuscular skill is also critical to mechanical efficiency because the more skillful athlete will activate only those muscle fibers required to produce the appropriate movements. Extraneous muscle contractions require more energy expenditure but do not contribute to effective power output.

Introduction

The criterion for success in many sports, including those involving running, swimming, bicycling, speed skating, rowing, and cross-country skiing, is simply the time required to propel the athlete's body (and essential equipment such as a bicycle, rowing shell, or skis) for a given distance. In the case of Olympic weightlifting and power lifting, success is determined by how much weight can be lifted in the appropriate movements, whereas a wrestler is judged by the degree of physical control over the opponent. These sports are quite different in terms of the patterns of muscle recruitment, the force and power produced, and the equipment used; nevertheless, success in all of these seemingly diverse sports depends on a complicated application of a simple principle--the champion is the athlete best able to reduce the resistance or drag that must be overcome in competition and best able to sustain an efficient power output to overcome that resistance or drag (Figure 1)(Coyle et al., 1994). This review provides an analysis of the major factors that contribute to an athlete's ability to produce power appropriately to overcome resistance or drag and a number of important applied principles designed to help trainers, coaches, physiologists, and others assist athletes in achieving their goals in sport.


Table 1: mode of the interrelationship of major factors determining sport performance. Performance is determined by how effectively the athlete can sustain sufficient power output to overcome various types of resistance or drag, depending on the sport event. Sustainable power output depends on the rate of energy expenditure that can be sustained throughout the event and the efficiency with which that energy can be converted into mechanical power. Depending on the sport event, sustainable energy expenditure will be a function of the ability to sustain the production of energy by anaerobic and/or aerobic means. Mechanical efficiency is dependent on muscle efficiency, i.e., the efficiency with which muscles convert the energy stored in carbohydrate and fat into muscle shortening, and the neuromuscular skill with which the athlete performs the event, i.e., the degree to which the athlete has learned to recruit only those motor units required to produce maximal power output in a skillful way.

Resistance and drag: Examples in Sport

Examples of resistance in sport include the mass of a barbell in Olympic lifting or power lifting, the muscular efforts of an opponent in wrestling or judo that are used to offset the movements of a competitor, and the effect of gravity on resisting a marathon runner's ability to move up a hill. A lifter who can sustain adequate power output long enough to correctly lift a greater weight than a competitor will beat that competitor. Likewise, a competitor in wrestling or judo who can sustain power sufficient to overcome the resistance provided by the opponent throughout the match will be the winner.

Drag is a special case of resistance in which the friction of air or water around a competitor retards forward motion. Obvious examples of drag are the adverse effects of a headwind on the forward velocity of a competitive cyclist and the retarding effects of water drag on the efforts of a swimmer to move quickly ahead. In cycling on a flat course at speeds greater than 13 km/h (8 mph), most of the resistance to the power generated by a bicyclist is created by the air through which the cyclist's body moves; relatively little bicycling power is lost to friction of the moving components of the bicycle or to the rolling resistance of the contact between the tire and road (Kale, 1991). It is also important to realize that the air drag increases as the square of the velocity of the moving object, i.e., if speed is doubled, the drag increases by four-fold (Kale, 1991).

Air drag offers great resistance in any sport requiring the athlete to move at relatively high velocities; such sports include speed skating--30-40 km/h (19-25 mph) at distances of 0.5-10 km (3-6 mi)--and sprint running--25-35 km/h (15-22 mph) at distances of 100-400 m. In fact, the air creates so much resistance in speed skating that the skaters must assume a tightly crouched posture to reduce their frontal areas exposed to air. Although this posture reduces leg power, it reduces air drag to an even greater extent and thus produces higher skating velocities. Swimmers move at relatively low velocities because they encounter large drag forces from the water as well as from the turbulence at the surface of the water. This drag encountered by a swimmer is not simply a function of body mass, but also of the geometry of the body as it moves through the water.

It is obvious that in events such as bicycling, speed skating, and possibly sprint running, each of which requires the athlete to move through the air at high speeds, the ultimate race time will be determined by the power generated relative to the air resistance. The same is true for the swimmer who must overcome the drag of the water at lower speeds. The main point is that the race velocity in these sports is a function of power production relative to the drag encountered at racing speeds. Therefore, velocity (performance) can be increased by improving power output and/or by reducing drag.

Reducing resistance and drag

In some sports, such as Olympic lifting, power lifting, and the shot put, the very nature of the competition makes it impossible to reduce resistance. If a competitive lifter chooses a low resistance--a lightweight barbell, that athlete is unlikely to win the competition. Likewise, the rules do not allow a shot putter to choose a lightweight shot. However, there are methods that can be used in many sports to reduce resistance or drag. Here are a few examples:
Use Skillful Technique. Competitors in wrestling, judo, rugby, American football, and other "contact" sports can reduce the resistance applied by opponents by skillful misdirection movements that trick the opponents into resisting in the wrong direction. These techniques are learned through many years of practice under the instruction of skillful coaches.

Use Aerodynamic and Hydrodynamic Equipment and Body Postures. In some sports, effective techniques have been employed to reduce resistance and drag in air and water. The designs of golf balls and javelins have become more aerodynamic over the years, and the resulting reductions in air drag have improved the flight characteristics of both. In cycling, riders wear aerodynamic helmets and skintight clothing and assume crouch positions over the handle bars ("aero bars") to minimize wind resistance. In swimming, body position in the water and stroke mechanics are optimized by careful study of underwater videos so that the swimmer reduces water drag as much as possible. Also, engineers have successfully modified the designs of rowing shells, canoes, kayaks, sailboats, oars, and paddles to minimize water drag in competitive events.

Reduce Body Mass. Athletes should carefully consider whether they can effectively reduce resistance or drag by reducing body weight. For pole vaulters, high jumpers, long jumpers, and triple jumpers, gravity is the principal resistance that must be overcome, and body weight is responsible for nearly all of this effect of gravity. Therefore, if these athletes can reduce their body weights without equivalent reductions in their abilities to skillfully generate muscular power, their performances should improve. Of course, if the body weight loss leads to a serious loss of muscular power, performance may well be worsened, not improved. Competing at an effectively low body weight is also critical for distance runners, endurance cyclists, and cross-country skiers. In these sports, the resistance of gravity is a crucial factor in determining performance; in addition, at the higher velocities of cycling, air drag is a major type of resistance that must be overcome, and a smaller frontal body surface area can reduce that resistance.

Weight reduction is not so much of an issue in swimming because the body mass is buoyed up by being immersed in water. However, to the extent that reductions in body weight help reduce water drag, weight loss could be of benefit in swimming, too. Differences in swimmers' individual body builds could play a significant role in determining whether or not weight loss improves swim performance. For example, weight loss may be quite ineffective in a swimmer who already presents a small frontal area and who tends to lose weight mostly in the thighs. However, if a swimmer has exceptionally large shoulders and a large chest, and if the mass of these areas can be reduced effectively through a weight loss program, such an approach could shave time off that swimmer's personal records.

Providing efficient sustained power output to overcome resistance and drag

Power is the ability to apply force through a distance quickly. In other words, power can be thought of as a combination of strength and speed. Interestingly, the sport of power lifting is misnamed because only strength, not speed, is required to be successful; as long as the barbell is moved appropriately, time is of no importance. On the other hand, a person could have exceptionally strong leg muscles and be a pitiful high jumper, sprinter, or long jumper if that strength could not be brought to bear quickly.

Unfortunately, absolute maximal muscular power can be sustained for only a fraction of a second. Thus, assuming equal resistance or drag, the champion in a sport event will not necessarily be the competitor who can produce the greatest maximal power, but instead will be the one who can sustain the greatest power output to overcome the resistance or drag for the duration of the event. This duration may be only a second or two, such as in power lifting, or many hours, such as in an Ironman triathlon.

The ability to sustain a high power output to efficiently overcome resistance or drag involves two major factors--the ability to sustain energy production by the muscles and the ability to apply that muscular energy efficiently to overcome resistance or drag.


Sustaining energy production by the muscles

When energy requirements are extremely high, such as during a sprint in track or swimming or during an Olympic weightlifting event, most of the muscular energy is supplied by two fuels, phosphocreatine (PCr) and glycogen, that are stored in small amounts in the muscles. Because these two fuels can be broken down for energy without the use of oxygen, this is known as anaerobic (without air) energy production. Aerobic energy production occurs at a much slower rate as fats and carbohydrates are broken down with the aid of oxygen in the muscles.

Sustainable Energy Expenditure in Brief, High-Power Events

Brief, high-power activities such as weightlifting and sprinting rely largely on the anaerobic breakdown of PCr and muscle glycogen for energy. When estimates of anaerobic energy production are coupled with simultaneous measurements of aerobic energy production, the approximate relative contributions of these two energy sources during various phases of exercise lasting from 0-180 s are as shown in Table 1. It is clear from the table that the percentage anaerobic contribution to energy production falls off rapidly as the exercise duration increases.

Both PCr degradation and anaerobic glycolysis are activated instantaneously at the onset of high-intensity exercise. Measurements of PCr and lactate from muscle biopsies taken following as little as 1-10 s of electrical stimulation (Hultman & Sjoholm, 1983) and after sprint cycling (Boobis et al., 1982; Gaitanos et al., 1993; Jacobs et al., 1983) confirm the rapid breakdown of PCr and rapid accumulation of lactate. At the onset of less intense exercise, a similar instantaneous activation of both PCr degradation and anaerobic glycolysis occurs but at a much slower rate because the mismatch between energy demand and aerobic supply is reduced during submaximal exertion.

Rate of Anaerobic Energy Production During Exercise

The rate of anaerobic energy provision is critical to success in sports that require the development and short-term maintenance of high power outputs. World-class power lifters and weightlifters can produce power outputs that are 10-20 times that required to elicit the maximal rate of aerobic energy provision, which is estimated by the maximal rate at which the athlete can consume oxygen (VO2max). However, such high power outputs can be maintained for only a fraction of a second. Sprinters can achieve power outputs that are 3-5 times the power output that elicits VO2max, but they can sustain that power output for only about 10 s. However, power output over a 30-40 s sprint can still be sustained at twice the power output at VO2max. Estimates of the rates of anaerobic provision of energy have been calculated from biochemical changes in muscles following intense exercise lasting from 1.3 to 200 s (Spriet, 1994). These studies used non-elite athletes who performed sprint cycling, sprint running, or repeated knee extensions or who underwent electrical stimulation of their muscles. The highest measured rates for energy production from PCr and anaerobic glycolysis during various types of exercise lasting from 1.3-10 s were each approximately 250-500% of the estimated maximal rate of energy provision from aerobic metabolism. In other studies of sprint cycling for 6-10 s, energy production rates from PCr and anaerobic glycolysis combined were about 400-750% of that during maximal aerobic metabolism (Boobis et al., 1982; Jacobs et al., 1983).

The anaerobic energy provision rates decrease when averaged over longer periods of time. In studies that examined intense exercise for 30 s, the average energy provision rate from PCr was about 70-100% of that from maximal aerobic metabolism; anaerobic glycolysis provided energy at a rate estimated to be 220-330% of that from maximal aerobic metabolism (Spriet, 1994). The large decrease in energy produced from PCr when averaged over 30 s, as compared to less than 10 s, indicates that the PCr store becomes depleted between 10 and 30 s of intense exercise. Thus, for maximal exertion lasting longer than about 30 s, it appears that only glycolysis can provide for further anaerobic energy production.

Anaerobic Energy Production During Intermittent High-Power Exercise

Many athletes repeatedly engage in bursts of high-intensity exercise with varying amounts of recovery time between exercise bouts. Examples include a wide receiver in American football, a basketball player in repeated fast break situations, or a swimmer or track athlete during interval training. Most of the energy for short bouts of high-intensity exercise is derived from anaerobic sources; therefore, the ability to recover during rest periods is essential for success in this type of activity. Many studies have examined the performance effects of intermittent high intensity exercise, but few have examined the anaerobic metabolism associated with this type of metabolic stress. Examples of the exercise models that have been studied and provided some conclusions include: 10 bouts of sprint cycling, each lasting 6 s with rest periods of 30 s; four bouts of sprint cycling for 30 s with 4-min rest periods; and two bouts of knee extension exercise to exhaustion in 3 min with 10-60 min of recovery (Bangsbo et al., 1992; Gaitanos et al., 1993; McCartney et al., 1986). Muscle biopsy measurements demonstrated that PCr was decreased by approximately 50% after 6 s and by 75-80% during longer sprints. The PCr is quickly resynthesized during recovery, reaching 50% of rest values by 30-60 s and about 80% by 2-4 min. With repeated sprinting, energy production from anaerobic glycolysis is progressively more difficult to achieve. Presumably, the accumulation of lactic acid in the active muscles plays a major role in the inability to continue producing energy by anaerobic glycolysis. Therefore, after repeated bursts of exercise, PCr is the only potential anaerobic energy source that can be relied upon. However, as described above, it is essential that adequate rest be provided in between intermittent exercise bouts to allow PCr stores to be replenished in the muscles.

Sustained Aerobic Energy Production

The maximal rate of aerobic energy production (VO2max) can be sustained for only about 8-10 min by elite athletes. In events lasting longer than 8-10 min, the best competitor among those with similar values for VO2max is usually the one who can sustain aerobic energy production at the greatest proportion of his or her maximal rate, that is, at the greatest percentage of the VO2max. This in turn is largely dependent on the extent to which the athlete can produce energy aerobically at a high rate without accumulating a large amount of lactic acid in the blood. In other words, the athlete who produces a large amount of lactic acid at a given speed of running, swimming, or cycling cannot continue to perform at that pace for as long as the athlete who does not accumulate as much lactic acid. An athlete who has the ability to exercise at a high intensity before blood lactic acid begins to accumulate is said to have a high lactate threshold (Coyle et al., 1988; Holloszy & Coyle, 1984). An athlete's lactate threshold seems to be a better indicator of endurance performance lasting 30 min to 4 h than does the VO2max (Coyle et al., 1988, 1991).

This is because the lactate threshold is a better index of the athlete's ability to sustain a high rate of energy expenditure for the duration of the competition.

Role of Nutrition in Determining Sustainable Energy Production

Two nutrients, carbohydrate and water, are the dietary constituents that have repeatedly been shown to be most important for optimizing endurance performance. Muscles obviously cannot produce energy without fuels derived from nutrients obtained in the diet, and carbohydrate is an obligatory fuel for high-caliber sport performance. It is well established that dietary carbohydrate consumption before, during, and after exercise can make an important contribution to performance. Carbohydrate consumption acts primarily by increasing the body's stores of glycogen in muscles and in the liver before exercise and by increasing the availability of glucose for use by the muscles during exercise (Coggan & Swanson, 1992; Costill & Hargreaves, 1992; Coyle, 1991; Williams, 1993). Fluid intake during prolonged exercise is also required to counteract the debilitating effects of exercise and heat on cardiovascular function and on body temperature regulation. When dehydration reduces blood volume, oxygen delivery to the muscles by the blood can be compromised, and this reduces the ability of the muscles to produce energy aerobically. Dehydration also compromises the ability of the body to regulate its temperature, resulting in eventual lethargy and potential heat illness, both of which adversely affect the athlete's ability to sustain a high rate of energy production. Carbohydrate-electrolyte beverages are advocated as the most effective way to supply both carbohydrate and fluid to the body during exercise (Coggan & Swanson, 1992; Gisolfi & Duchman, 1992).

Improving the ability to sustain energy production at a high rate

Here are some ways that athletes may be able to improve their abilities to sustain high rates of energy production so they can sustain greater power output to overcome resistance and drag:
At the onset of a training season, the athlete should establish a solid aerobic training foundation by training at relatively low intensities for long durations. This will help develop a greater blood volume, an improved ability of the heart to pump blood, and better networks of capillaries in the trained muscles. These cardiovascular adaptations will lead to an improved delivery of oxygen to the muscles and an enhanced ability of the muscles to sustain high rates of aerobic energy production.

For the bulk of the athlete's training, the specific muscle groups involved in the competitive event should be overloaded, and the athlete should train at a pace or intensity similar to that used in competition (Hickson, 1977, 1985). Such training can lead to improved stores of glycogen and PCr in the trained muscles so that greater energy reserves will be present in the muscles before competition begins. Furthermore, metabolic adaptations to this type of training are likely to enhance the ability of the muscles to utilize fat for energy and to spare muscle glycogen, resulting in less lactic acid production and less accumulation of lactic acid in the blood at a given pace or intensity (Holloszy & Coyle, 1984). This means that the athlete's lactate threshold will be increased so that aerobic energy production can be sustained longer at a greater rate than was possible before training.

During high intensity, anaerobic interval training, the duration of recovery intervals should be sufficient--usually between 30 s and 4 min--to allow the muscles to replenish most of the PCr depleted in the previous exercise interval. If these recovery intervals are too brief, the supply of PCr in the exercising muscles will be inadequate to provide energy anaerobically at a high rate (Gaitanos et al., 1993; McCartney et al., 1986). This means that the athlete will be forced to exercise at a lower intensity (slower pace) and that inappropriate muscle groups may be recruited to accomplish subsequent exercise intervals. If these events occur, the athlete will be learning incorrect movement patterns during training that may adversely affect competitive performance.

The athlete should receive adequate rest--approximately 24 h--between exhaustive training sessions to allow for total replenishment of depleted glycogen stores in the muscles prior to the next training session (Coyle, 1991). Otherwise, the quality of the next training session may be compromised because the athlete's muscles will be easily depleted of one of their main fuels. In addition, training intensity and duration should be gradually reduced during the week before a competitive event so that the athlete's energy reserves are fully loaded before competition.

The athlete should drink plenty of fluids before, during, and after exercise to avoid becoming dehydrated. Dehydration can lead to a diminished ability to deliver oxygen to the muscles, heat cramps, heat exhaustion, and even heat stroke, all of which can impair muscular energy production.

On a daily basis, the athlete should consume a diet high in carbohydrate, about 8 g of carbohydrate per kilogram of body weight (4 g/lb). This will ensure that the muscles can store extra glycogen and may help sustain energy production during competition.

Preliminary evidence suggests that dietary creatine supplementation may increase PCr stores in muscles (Dalsom et al., 1995) and perhaps improve performance in events such as fastbreak basketball that require repeated brief exertions. The extent to which creatine supplementation proves to be useful in actual sport settings remains to be seen.

During prolonged exercise, the athlete should consume carbohydrate-electrolyte drinks containing approximately 6% carbohydrate (glucose, sucrose, or maltodextrins) and a small amount of sodium to help maintain an adequate carbohydrate energy supply to the muscles and to minimize dehydration. Volumes of 150-250 mL (5-8 oz) should be consumed every 15-20 min to replace most, if not all, of the sweat lost by the athlete during exercise (Montain & Coyle, 1992).

Mechanical efficiency: A major determinant of effective power output

Mechanical efficiency for a sporting event is the ratio of the mechanical power output to the total energy expended to produce that power. Typically, both power output and energy expenditure are expressed in watts (W), and the ratio is expressed as a percentage. For example, if a cyclist expends energy at the rate equivalent to 5 L of oxygen per minute (1745 W) to produce 400 W of power on a bicycle ergometer, the mechanical efficiency would be (400/1745) 100 = 23%. Two of the principal factors that determine the mechanical efficiency of an athlete in a sport event are 1) the efficiency with which the active muscles convert the chemical energy stored in carbohydrate and fat to the mechanical energy required to shorten the contractile elements in the muscles, and 2) the neuromuscular skill with which the athlete performs the event.

Role of Muscle Efficiency in Determining Mechanical Efficiency

Muscle efficiency has two components, the first of which is the efficiency with which chemical energy from carbohydrate and fat is converted to adenosine triphosphate (ATP), the only form of chemical energy that can power muscle contraction. The process of ATP synthesis is about 40% efficient, i.e., 40% of the metabolic energy in carbohydrate and fat is transferred into ATP synthesis, whereas 60% of the energy is lost as heat (Kushmerick, 1983; Kushmerick & Davies, 1969). This efficiency of ATP synthesis is fairly constant among individuals.

The second component of muscle efficiency, i.e., the efficiency with which the energy released during ATP hydrolysis is converted to muscle fiber shortening, is more variable than is the efficiency of converting stored fuels to ATP. The efficiency of ATP hydrolysis is dependent on the velocities of muscle contraction (Goldspink, 1978; Kushmerick & Davies, 1969). A peak efficiency of approximately 60% or more can be elicited from myofilaments contracting at one- third of maximal velocity; i.e., the velocity of peak efficiency (Kushmerick, 1983; Kushmerick & Davies, 1969). Thus, slow-twitch muscle fibers obviously have slower velocities of peak efficiency than do fast-twitch fibers (Fitts et al., 1989).

Mechanical efficiency when cycling at 80 rpm is directly related to the percentage of slow- twitch muscle fibers in the vastus lateralis muscles (Coyle et al., 1992). It seems that when cycling at this cadence, the velocity of muscle fiber shortening in the vastus lateralis is close to one-third maximal velocity of the slow-twitch fibers (Coyle et al., 1992). This makes slow-twitch muscle fibers substantially more efficient than fast-twitch muscle fibers at converting ATP into muscular power when cycling at 80 rpm (Coyle et al., 1992; Goldspink, 1978).

Muscle fiber type has a large effect on mechanical efficiency, which in turn has a large influence on sustainable power output as measured during a 60-min bout of cycling in a homogeneous group of cyclists (Horowitz et al., 1994). The cyclists in this study were paired and divided into two groups based upon the percentage (i.e., above or below 56%) of slow-twitch muscle fibers in their vastus lateralis muscles. One group possessed a normal distribution of fiber types, with an average of 48% slow twitch fibers. The other group had 72% slow-twitch fibers on average. These two groups were identical in VO2 max as well as in the VO2 maintained during the ride. Therefore, they possessed the same aerobic energy expenditure potential for this type of task. However, the cyclists with a high percentage of slow-twitch fibers displayed significantly higher mechanical efficiencies and were therefore able to sustain a 9% greater power output (342 W vs. 315 W) during the 60-min ride. Clearly, endurance cycling performance is heavily influenced by mechanical efficiency, which in turn appears to be dependent on the rider's muscle fiber type profile and the efficiency of ATP hydrolysis by the muscle.

Role of Neuromuscular Skill in Determining Mechanical Efficiency

No matter how efficiently one can transform chemical energy into mechanical energy in a given muscle fiber, the overall mechanical efficiency in a sports event will be poor if the athlete is poorly skilled. A good example of the importance of skill is the contrast in the freestyle swimming performances of novice and elite swimmers. The novice may produce a great deal of power, but because the swimmer is so unskillful, the power output is misdirected so that lots of thrashing about occurs with little forward velocity. The elite swimmer, on the other hand, has learned to swim rapidly and gracefully, using only those muscle fibers required to execute the stroke effectively. Neuromuscular skill obviously plays a greater role in determining the mechanical efficiency for some sports, e.g., swimming and wrestling, than it does for others, e.g., running and power lifting, but even small differences in skill can have a major impact on performance in any sport at the elite level.

Improving the athlete's ability to provide power output in an efficient manner

There is little that the athlete can do to improve muscle efficiency because the chemical efficiency of converting fuels to ATP and the proportion of slow-twitch fibers involved in various movements are largely determined by heredity. An exception may be that athletes over many months of training may learn to recruit more of the efficient slow-twitch muscle fibers and fewer of the less efficient fast-twitch fibers. In addition, there are three important steps that can be taken to improve the skill with which power output is applied.

The athlete should obtain the technical advice of competent coaches who can explain how movement patterns should be altered to become more skillful. Often the coach can rely upon personal experience and observation to make critical improvements in an athlete's technique.

Video analysis of the athlete's performance can provide clues about changes in movement patterns that can be made to improve efficiency. The assistance of a sport biomechanist or a coach well-educated in biomechanics could be important in this phase of the athlete's preparation.

The athlete must repeat the appropriate movement patterns in a skillful manner many thousands of times during practice so the nervous system learns to perform the movement correctly every time throughout the entire duration of competition. There is no substitute for skillful repetition of muscular activities to ensure that such activities are likely to remain skillful in the heat of competition.

Summary

For most competitive sports, improving the performance of an athlete can be accomplished by reducing the resistance or drag that must be overcome or by increasing the athlete's ability to sustain a high power output to overcome that resistance or drag. Reducing air resistance or water drag typically involves improving body position in the air or water by minimizing the frontal surface area of the athlete that is exposed to the air or water. Sometimes the apparel or equipment used in the sport, e.g., helmets, swimwear, bicycles, and rowing shells, can be made more aerodynamic or hydrodynamic to reduce resistance or drag.

Increasing sustainable power output requires that the athlete undergo a carefully designed training program that will improve the athlete's abilities to: 1) produce metabolic energy by both aerobic and anaerobic means, 2) sustain aerobic energy production at high levels before lactic acid accumulates excessively in the blood, 3) recruit more of the efficient slow-twitch muscle fibers at exercise intensities used in competition, and 4) become more skillful by recruiting fewer non- essential muscle fibers during competition. Careful attention to maintaining a sufficient intake of fluids and carbohydrate before, during, and after strenuous competition and training sessions is also important.

Although it is apparent that some uniquely gifted athletes are able to win consistently even when their approaches to training are obviously not optimal for reducing resistance or drag and for enhancing their sustainable power outputs, it is clear that such athletes cannot achieve their full potentials in sport without addressing these two basic principles.

* This article was adapted from "Introduction to Physiology and Nutrition for Competitive Sport," by E.F. Coyle, L. Spriet, S. Gregg, and P. Clarkson, which appeared in D.R. Lamb, H.G. Knuttgen, and R. Murray (eds.), Perspectives in Exercise Science and Sports Medicine, Vol. 7: Physiology and Nutrition for Competitive Sport. Carmel, IN: Cooper Publishing Group, 1994, pp. xv-xxxix. The author is especially grateful to Edward Coyle, Ph.D. and Lawrence Spriet, Ph.D. who contributed much of the text for this article.

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• Horowitz, J.F., L.S. Sidossis, and E.F. Coyle (1994). High efficiency of Type I muscle fibers improves performance. Int. J. Sports Med. 15:152-157.
• Hultman, E., and H. Sjoholm (1983). Substrate availability. In: H.G. Knuttgen, J. A. Vogel, and J. Poortmans (eds.) Biochenistry of Exercise, Vol. 5. Champaign, IL:Human Kinetics, pp. 63-75.
• Jacobs, I., P. Tesch, O. Bar-Or, J. Karlsson, and R. Dotan (1983). Lactate in human skeletal muscle after 10 and 30 s of supramaximal exercise. J. Appl. Physiol. 55:365-367.
• Kushmerick, M.J. (1983). Energetics of muscle contraction. In: L.E. Peachey, R.H. Adrian, and S.R. Geiger (eds.) Handbook of Physiology, Section 10: Skeletal Muscle. Bethesda, MD: American Physiological Society, pp. 189-236.
• Kushmerick, M.J., and R.E. Davies (1969). The chemical energetics of muscle contraction II. The chemistry, efficiency, and power of maximally working sartorius muscle. Proc. R. Soc., Ser. B. 1174:315-353.
• Kyle, C.R. (1991). Ergogenics of bicycling. In: D.R. Lamb and M.H. Williams (eds.) Perspectives in Exercise Science and Sports Medicine, Vol 4: Ergogenics--Enhancement of Performance in Exercise and Sport. Carmel, IN: Brown & Benchmark, pp. 373-413.
• McCartney, N., L.L. Spriet, G.J.F. Heigenhauser, J.M. Kowalchuk, J.R. Sutton, and N.L. Jones (1986). Muscle power and metabolism in maximal intermit-tent exercise. J. Appl. Physiol. 60:1164-1169.
• Montain, S.J., and E.F. Coyle (1992). The influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. J. Appl. Physiol. 73:1340-1350.
• Spriet, L.L. (1994). Anaerobic metabolism during high-intensity exercise (Chapter 1). In: M. Hargreaves (ed.) Exercise Metabolism. Champaign, IL: Human Kinetics (In press).
• Williams, C. (1993). Carbohydrate needs of elite athletes. In: A.P. Simopoulos and K.N. Pavlou (eds.) World Review of Nutrition and Dietetics, Vol. 71: Nutrition and Fitness for Athletes. Basel: Karger, pp. 34-60.

The Gatorade Sports Science Institute® was created to provide current information on developments in exercise science, sports nutrition, and sports medicine and to support the advancement of sports science.


Wednesday
Aug312011

Body Fat Control and Making Weight

By: Sports Dietitians Australia.
From: Sports Dietitians Australia: Fact sheet: Fuelling Fitness for the Future.
PDF link: Body Fat Control and Making Weight


What is my ideal weight?

Body weight is a poor indicator of fatness in active people. Changes in weight can be due to fluid losses as sweat, food still being digested from the last meal and changes in the level of muscle glycogen (every gram of glycogen is stored with approximately 3 g of water). Since training, especially weight training, increases muscle mass, skinfold measurements are a better guide to fatness than body weight. When you are training two or more times a day, shifts of fluid and glycogen stores can result in daily weight fluctuations of around 2 kg.

Elite athletes strive to achieve low body fat levels for competition. There are clear performance benefits to being light and lean in sports like triathlon, marathon running, swimming and gymnastics. However, body type is under genetic control and each person has a different capacity for leanness. In sports like figure skating, gymnastics and diving, elite performers are naturally small and light.

In sports where athletes compete in weight divisions (eg lightweight rowing, boxing, weightlifting), there is often pressure to manipulate body weight and fat levels to make a lower weight category.
In desperation, some competitors resort to rapid weight loss methods prior to ‘weigh in’ on the day. Strategies to make weight, such as severe food restriction, excessive exercise and dehydration are dangerous and in the longer term can result in poor health, psychological problems and eating disorders.

The ideal weight for an athlete needs to take into account:
• their height and frame size;
• their natural body weight;
• scientific evidence for a competitive advantage by achieving a certain body weight or body fat, and;
• An athlete’s own experience of how easy is it to achieve
and perform at a new body weight or fat level.

A smart athlete will choose a sport or category better suited to their physique, where they can concentrate more on performance and feeling good than becoming pre-occupied with weight and fat loss.

Do kilojoules count?

Over the past decade there has been increased emphasis on dietary fat intake. There is no doubt that too much fat in the diet increases the risk of overweight. Fats are energy dense (37 kJ/gram) compared to proteins (17 kJ/gram) and carbohydrates (16 kJ/gram). The fat we consume is also stored more efficiently in the body than either protein or carbohydrate. Clearly, reducing dietary fat intake is one of the most effective strategies in promoting weight loss. Does that mean we can eat unlimited amounts of low fat foods? That depends on how active you are. Most active individuals can eat as much low fat food as they like and stay lean. For the ‘couch potato’, it is still important to get up and get moving. Eating a lot of low fat food when inactive will not help weight loss. Energy balance (kilojoules or calories consumed vs burnt) is still an important factor in fat loss for sedentary or moderately active individuals. Although they don’t need to count calories, less active people need to eat a moderate, rather than a large, amount of low fat food. The same applies to athletes who need to maintain their body weight below what is natural for them e.g. jockeys, light weight rowers, boxers, gymnasts, and dancers. 

Dangers of Dehydration

Dehydration is often used as a quick way to ‘make weight’. Fluid loss of as little as 1% of body weight will decrease performance, especially in sports like light weight rowing or boxing where a combination of strength and endurance is needed. Other side effects of dehydration include:
• Fatigue
• Nausea
• Cramping
• Poor co-ordination and reaction time (can result in serious injury depending on the sport)

With significant fluid loss (greater than 2% of body weight) effects include:
• Increased body temperature resulting in heat stress/exhaustion
• Muscle breakdown
• Impairment of kidney function
• Electrolyte imbalance
• Circulatory and eventually heart failure
Dehydration to make weight has been associated with a number of deaths in otherwise healthy, fit individuals

Exercising for Fat Loss

Although low intensity exercise is recommended for those starting an exercise program (or with a medical problem), fitter, healthy individuals gain more benefit by increasing the intensity as their fitness improves.

Higher intensity exercise burns up more calories, promoting fat loss. Although lower intensity exercise (say about 50% maximum aerobic capacity or maximum heart rate) uses a higher percentage of fat for fuel, the total amount of fat used is less than for high intensity exercise.

It is often assumed that to burn fat, exercise intensity must be kept low. However, the bar graph shows that the amount of fat used is higher at 65% of maximal aerobic capacity (65% VO2max) than at 25%. At 25% VO2 max, fat accounts for almost all the energy used during exercise. However, the total number of calories expended over 30 minutes, is substantially lower (190 calories) than at 65% of VO2 max (420 calories). Although only 50% of the energy expended at 65% VO2 max is derived from fat, over the 30 minutes of exercise, this is a much greater amount of fat (210 calories of fat) than what is burnt at 25% VO2 max (150 calories of fat).

It is important to remember that aerobic training improves the body’s ability to burn fat, even when working at moderately high exercise intensities (around 60-70% VO2 max or maximal heart rate). To optimise fat loss, you need to work continuously for at least 30-60 minutes. As you get fitter you can exercise harder and still be in the ‘fat burning’ zone.

A comfortably challenging pace optimises both fat and calorie use, burning more fat in less time. Remember, untrained people need to start slowly. There is also benefit in accumulating three 10-minute periods of low intensity physical activity a day for those less interested in exercise.

Moving more by increasing incidental exercise (eg taking the stairs, walking to work) is a key weight control strategy.

Essential strategies for weight (fat) loss or making weight
• Choose a body fat/weight that keeps you healthy in the long term.
• Choose a balanced diet, emphasising a low-modest fat intake.
• Eat a little less energy (kilojoules/calories) than you burn in training or competition to achieve a slight calorie deficit, and therefore a healthy weight (or body fat) loss. Don’t crash diet.
• Learn how to handle eating out socially and include treats. You should not become obsessed about, or even frightened of, the occasional splurge.
• Have a training program that complements your weight (fat) loss strategies. If you need to make a specific competition weight, heavy weight training may need to be reduced or balanced with aerobic training.
• Be wary of times when weight (fat) levels may fluctuate more, for example ‘off season’ or injury. Monitor these changes and adjust your dietary intake and training to suit.
• Gradually reduce weight (not more than 0.5-1.0 kg per week) or 2-5 mm of fat each week if using skinfold (the pinch test) measurements.
• Train not more than 2.0 kg away from your optimal competition weight.
• Seek professional advice from a sports dietitian on dietary requirements for your sport, or whether a weight category or body fat level is realistic for your physique.

Low carbohydrate diets – just another low kilojoule diet

Just when most people appreciate that high carbohydrate foods like bread and potatoes are not fattening, a new era of carbohydrate controversy has emerged. A range of reduced or low carbohydrate diets has captured the imagination of athletes and fitness enthusiasts alike.

These diet plans commonly restrict the choice of foods you can eat and make meals more difficult to arrange because there are so many rules to follow.

The end result is that they all become a low calorie diet in disguise. At the start followers do not notice that they are eating much less, sometimes as low as 4000 kilojoules per day! This is less than half the calorie needs of a sedentary adult female.

It is no wonder short-term weight loss occurs. The claim made by low carbohydrate diet pushers that “fats are not fattening” is not supported by scientific research that provides a strong link between dietary fat intake and excess body fat. Following any low kilojoule and low carbohydrate diet, increases the risk of muscle loss and fatigue. See our Fact Sheet number 20 on Low Carb diets for weight loss in athletes.


Wednesday
Aug102011

Tailoring Nutrient Intake to Exercise Goals

By: Phil Block, M.S., & L. Kravitz, Ph.D.
From: Tailoring Nutrient Intake to Exercise Goals
Site Link: IDEA
Article Link: Tailoring Nutrient Intake to Exercise Goals


Introduction

Techniques of exercise periodization for developing muscular fitness have been made popular by a growing body of research (Fleck, 1999). Studies consistently demonstrate that periodization programs are among the most effective muscle strengthening exercise protocols that exist (Fleck, 1999). Although there is no single best periodization program that suits everyone due to individual differences such as gender, muscle fiber percentages, and genetics, undulating periodization programs have recently shown particular promise for optimizing muscular fitness benefits (Marx et al., 2001). It is hypothesized that distinctive training variations and modulation of the exercise stress and recovery patterns may lead to greater muscular adaptations in undulating periodization programs compared to more traditional approaches (Overturf & Kravitz, 2002). Most recently a unique opportunity for establishing a nutritional framework to support periodization programming has been suggested (Coyle, 2004). This dietary approach is referred to as nutrient periodization and focuses on adjusting the macronutrients to best support exercise periodization techniques. The rationale and implementation of this new training application is presented and discussed in this article.

What’s the basis of nutrient periodization?

Nutrient periodization is a robust system of fluctuating macronutrient (carbohydrate, fat, and protein) intake that works in concert with the most current exercise and nutrition research for muscle strength and hypertrophy. In addition, it is supported and driven by the recent 2005 Dietary Guidelines for Americans (HHS & USDA, 2005). Thus, it is a balanced dietary program that fitness trainers, their clients, and scientists can all embrace.

How is nutrient periodization grounded in solid nutrition guidelines?

In 2002, the Institute of Medicine Food & Nutrition Board established new dietary guidelines for macronutrient consumption called the Acceptable Macronutrient Distribution Range (AMDR). The AMDR’s define the appropriate average ranges for dietary intake of carbohydrate, fat, and protein. These guidelines were designed to avoid nutrient deficiencies that seem to occur when macronutrient consumption consistently falls above or below the recommended levels. The AMDR recommendations have been incorporated into the 2005 Dietary Guidelines for Americans and advocate 45 and 65 percent of their total kilocalories from carbohydrates, 20 to 35 percent from fat, and 10-35 percent from protein. The AMDR’s allow for the dietary individualism that is necessary for meeting specific exercise goals, such as for building muscle and increasing muscular strength.

How do individuals interested in muscle hypertrophy benefit from this?

Athletes and serious exercise enthusiasts often engage in extreme intakes of protein, carbohydrate, or fat, while de-emphasizing other macronutrients at the same time. Although there may be a need to increase a particular macronutrient acutely, chronic unbalanced dietary practices may result in decreased performance, loss of muscle, and overall fatigue. Elevated protein intake (a common practice for building muscle as it results in maintained positive nitrogen balance) may decrease fat and carbohydrate consumption to levels that hinder performance and ultimately inhibit optimal muscle growth. Conversely, high carbohydrate diets (a necessity for recovery from intense training bouts) may edge out fat and protein, which has an entirely different repercussion, namely altered cholesterol profiles (American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada, 2000), depressed testosterone levels (Lambert et al., 2004), and overtraining (Venkatraman and Pendergast, 2002). This will ultimately lead to the inability to gain muscle mass. Therefore, nutrient periodization is a sensible practice for serious exercisers because it can modulate macronutrient intakes while reducing the chance of nutrient deficiencies over an extended period of time. It works by promoting a day-to-day fluctuation of macronutrient intake to match the exercise periodization needs for building muscle and gaining strength. It is important to note that because the AMDR recommendations give guidelines for average intakes, individual days can be below or above those recommendations. As long as the diet falls within those guidelines over the course of several days or a week, nutrient deficiency and disease risk will be low.

Why is kilocalorie intake important for building muscle and gaining strength?

Physiologically, the key to gaining muscle mass is to consume more energy than what is expended, while focusing on high-intensity resistance training (Lambert et al., 2004). Nutritionists and other health professionals have long understood the importance of tipping the energy scales in favor of excess kilocalorie consumption for muscle gain. Although this view may be criticized for being overly simplistic and sometimes ineffective, energy intake is usually considered a critical strategy for muscle gain.

The exact amount of excess kilocalories required to gain muscle is not clearly known, as the effects of metabolism, exercise, and nutrient status make pinpointing specific requirements difficult. Experts, however, recommend between 1000-3500 excess kilocalories over the course of a week to gain one pound of muscle. This number is based on several overfeeding studies and estimates of muscle gain (Manore & Thompson, 2000).

In real-world situations, hypertrophy may require higher levels of kilocalorie intake than this recommendation, with research suggesting approximately 44 to 50 kcal/kg body weight/day (Manore, Thompson & Russo, 1993). Some persons completing serious training may have even higher energy requirements. Based on this research, a 100 kg (220 pounds) individual attempting to build muscle might have a kilocalorie requirement of 4400-5000 kilocalorie a day or greater.

So, how many kilocalories should be consumed to build muscle?

The bottom line is increased kilocalorie consumption is necessary to build muscle. From the review of literature, a suggestion of at least 47 kcal/kg of body weight/day may be recommended, realizing that factors such as individual metabolism may bring that number higher or lower.

Why is protein intake important for building muscle and developing strength?

When an individual is resistance training (particularly heavy resistance training), there is an increase in the rates of both protein synthesis and in the breakdown of protein in muscle for at least 24 hours after a workout. Additional protein may be needed to, 1) help repair exercise-induced damage to muscle fibers, 2) promote training-induced adaptations in muscle fibers, and 3) assist with the replenishment of depleted energy stores (Gibala, 2004).

How much protein is needed to build muscle?

Optimal protein and amino acid ingestion is regarded as crucial for strength and hypertrophy. Individuals who consistently engage in moderate to high levels of exercise should consider a protein intake that exceeds the U.S. Dietary Reference Intake (DRI) of 0.8 g/kg/day (Lambert et al., 2004). However, in a recent review, Tipton and Wolfe (2004) state that there is confusion in the research as to what optimal protein intake is because the level of optimal protein intake in athletes is very different for varying activities and individual goals. For example, a strength athlete requires sufficient protein to maintain and gain muscle mass, while an endurance athlete is more concerned with simply maintaining muscle mass while improving performance. This requires the adjustment of protein recommendations to specific levels that have not yet been adequately researched.

According to a most recent position stand on nutrition and athletic performance, experienced male bodybuilders and strength athletes may consume 1.6 to 1.7 g/kg/day to allow for the accumulation and maintenance of lean tissue (American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada, 2000). Data on female strength athletes is not available, but there is no evidence to suggest that this level will not sufficiently meet the dietary requirements of female athletes as well.
Interestingly the impact of carbohydrate and fat on protein metabolism is a topic of current interest, with investigations suggesting there are anabolic concomitant effects of carbohydrate and fat on protein balance (Miller, Tipton, Chinkes, Wolf, & Wolfe 2003).

Current research on protein intake for building muscle indicates that higher levels of protein may drive muscle metabolism toward hypertrophy, and so the suggestion for muscle-building is to maintain a high protein intake within the current guidelines (Lambert et. al, 2004). A protein intake of 1.7 g/kg/day should optimally meet an exerciser’s muscle fitness gains.

Why is carbohydrate intake important for building muscle?

Varying exercise intensity is a key strategy to optimally building muscle. The current theory on the effectiveness of periodization programs is that very intense workouts will stress different muscle fibers than less intense workouts. This means that during an intense workout, certain muscle fibers will be activated while other fibers rest. Purportedly, alternating cycles of high-volume, low-intensity with low-volume, high-intensity provides a satisfactory stimulus/recovery for the different types of muscle fibers in the human body and minimizes the risk of overtraining (Overturf & Kravitz, 2002).

Stored carbohydrate (glycogen) is the predominant fuel source for moderate to high intensity activities. High intensity exercise takes a particular toll on glycogen stores because the availability of fat for fuel becomes limited at higher exercise intensities. When muscle glycogen stores are diminished, fatigue is eminent.

The replenishment of depleted muscle glycogen stores is of utmost importance to athletes and other very active people. If the stores are not recovered, the ability to exercise at a given intensity is greatly diminished, possibly leading to a detraining of the muscle (Burke, Kiens, & Ivy, 2004). When building muscle, especially through a periodization program, this is an important consideration because inadequate glycogen stores will decrease the exercisers ability to maintain appropriate exercise intensities. Resistance exercise may be particularly affected by decreased glycogen stores. Some research suggests drops of between 25-40% in total muscle glycogen during multiple-set resistance exercise to fatigue (Tesch et al., 1998).

How much carbohydrate should be consumed to build muscle?

Most active people report a diet of about 45-50% carbohydrate (about 5 grams carbohydrate/kg/body weight/day), which can easily support moderate bouts of exercise of about one hour per day (Hawley et al., 1995). Current literature recommends using absolute values of carbohydrate intake (g/kg) in reference to making recommendations for intake for adequate levels of glycogen replenishment from exercise. The recommendation is that athletes and recreational exercise enthusiasts seeking to maintain higher carbohydrate diets achieve a carbohydrate intake between 7-12 g/kg of body weight/day when attempting to restore glycogen stores after an intense workout (Coyle, 2004). This recommendation targets endurance exercise, but translates to prolonged, high intensity resistance workouts as well. The problem with this practice is a long-term high-carbohydrate diet may elevate serum triglyceride and interfere with muscle building by decreasing fat and protein intake.

Coyle (2004) proposes that a carbohydrate periodization approach bests resolves the long-term consequences of a diet too high in carbohydrates, yet meets the demands of the serious exerciser. The idea is that not every day of training requires a high intake of carbohydrate since not all days of exercise are intense or prolonged. Dr. Coyle (2004) writes, “Unfortunately, there has been little investigation of how best to vary carbohydrate intake on a day-to-day basis to match the typical alteration of hard, easy, and moderate days of training performed during a week by well-coached competitive athletes.” It is assumed that the most important objective of periodization of daily carbohydrate intake would be to ensure high muscle glycogen levels at the start of the hard training sessions. Serious exercise enthusiasts often perform 2-4 'hard' training sessions per week. To raise muscle glycogen to high levels, these exercisers should eat a total of 7-12 grams of carbohydrate/kg body weight during recovery from the last training session. The recovery period should be not be less than 24 hours (Burke, Kiens, & Ivy, 2004). However, during the 24 hours prior to a moderate or easy day of training, it may be satisfactory for serious exercisers to eat 5-7 grams of carbohydrate/kg. This nutrient periodization technique optimally accommodates macronutrient needs to the intensity fluctuations of periodized exercise programs.

A carbohydrate periodization plan for building muscle and increasing muscular strength?

Consider the following application from the research. After an intense workout, carbohydrate stores should be restored with a carbohydrate intake of 7-12 g/kg/day of carbohydrate (Coyle, 2004). Since most individuals trying to build muscle are not necessarily engaging in prolonged intense activity, it may be unnecessary to replenish with the upper end of the carbohydrate intake recommendation (12 g/kg/day) and thus achieve a more favorable macronutrient balance with a moderate approach. Therefore, an intake of 9 g/kg/day of carbohydrate for 24 hours following an intense workout may be ideal for individuals attempting to maximize muscular fitness gains. Further, after the carbohydrate stores have been replenished, high carbohydrate intake is no longer necessary focus and the exercisers can focus on the other macronutrients. During the 24-hour period prior to a moderate or light intensity activity, the fitness enthusiast attempting to build muscle may consider an intake of 6 g/kg/day of carbohydrate.

Is fat intake important for building muscle?

Fat is an essential nutrient in the human diet. In addition to providing energy, it is responsible for the transport of vitamins A, D, and E. Fat is also contained in every cell in the human body as a component of the cell membrane. If fat intake is too low, blood lipid profiles are affected, and various negative health and performance consequences may occur (Dreon et al., 1999). Since no sports performance-related benefits are associated with fat intakes below 15% (and health concerns would exist), experts do not recommend fat intakes below 15% of the total energy requirement (American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada, 2000).

Fat is an energy-dense substance, providing approximately 9 kcal/gram of energy. This makes the macronutrient a prime choice of foodstuff for recreational athletes building muscle. Healthful fat is an essential macronutrient for individuals attempting to maintain the high kilocalorie dietary needs of vigorous exercise for building muscle.

Some of the most exciting research on fat intake has examined its suspected contribution to minimizing the effects of overtraining. Overtraining is a major concern in exercise, as it severely diminishes the success of a fitness program. The use of Omega 3 Polyunsaturated Fatty Acids has been recently advocated as being a possibly effective way of reducing overtraining symptoms (Venkatraman and Pendergast, 2002).

How much fat is needed to build muscle increase muscular strength?

The current dietary recommendations for fat intake in the general public are to maintain fat intakes of between 20-35% of the total energy intake. This should be divided fairly evenly among saturated, polyunsaturated, and monounsaturated fatty acids. Chronic low fat diets (<15%) should be avoided because it may make it difficult for an exerciser to achieve a high kilocalorie diet, result in overtraining, negatively affect the lipid profile, and/or decrease exercise performance (Venkatraman and Pendergast, 2002). Chronic high fat diets (>35%) should be avoided because they may reduce carbohydrate and protein consumption, decrease long-term performance, reduce fat-soluble vitamin intake, and potentially increase the risk for cardiovascular complications (American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada, 2000). With the nutrient periodization approach to training, the suggestion is to allow fat intake to fill in the kilocalories after protein and carbohydrate levels have been established. When nutrient periodizing, carbohydrate levels after intense workouts will be high, so fat intake will be correspondingly low. When carbohydrate intake is low (prior to moderate or low intensity workouts), fat intake will be much higher, compensating for the low-fat intake days. In effect, this technique will moderate fat intake while allowing optimal fluctuations of carbohydrate.

Putting it together: A sample nutrient periodization approach to undulating periodization

Figure 1 depicts a sample nutrient periodization program for a 100 kg (200 pound) individual seeking to optimize muscle mass, while following the undulating periodization program initially shown in Figure 1. Relative macronutrient percentages fluctuate with exercise intensity to adequately facilitate recovery. Total kilocalorie intake for the exerciser is 4700 kilocalories/day (47 kilocalories/kg/day). Protein intake is maintained at 1.7 g/kg/day as the research does not yet support periodization of this nutrient. Carbohydrate intake changes from 6-9 g/kg/day depending on the intensity of the associated workout and fat intake adjusts to the carbohydrate and protein intake. Note that although on a day-to-day basis, macronutrient percentages fall outside the AMDR recommendations, over the course of the week the macronutrients are moderated. Fat intake averages ~20%, protein ~14%, and carbohydrate averages between 65-66%. In effect, the recommendations for carbohydrate replenishment from intense workouts are met, while also meeting the nutritional values from the Dietary Guidelines for Americans 2005. This presents a sensible, balanced approach for nutrition and periodization for building muscle.

The Bottom Line

Exercise periodization is a widely-used technique for optimizing muscle fitness benefits. Using an integrated approach of periodization-supportive nutrition is an evidence-based approach to maximizing these benefits.

Carbohydrate consumption is important to any activity, but it is particularly critical for intense workouts. Since periodization programs allow individuals to maximize intense workouts by designating the appropriate activity-to-rest fluctuation to allow optimal growth and recovery of muscle tissue, carbohydrate periodization is an attractive macronutrient approach to compliment the periodization program. For building muscle, a carbohydrate cycle of 6-9 g/kg/day should be developed around a particular periodization program.

The available protein research demonstrates the potential significance of elevated protein intake for building muscle. Current recommendations suggest that high protein intake may optimize muscle growth, so individuals seeking muscle growth and strength gains should consider maintaining protein intakes at toward the upper-end of the protein intake recommendations (1.6-1.7 g/kg/day).

Lastly, fat intake should be periodized in relationship to carbohydrate and protein intake to achieve the best results for building muscle and increasing strength on a periodized exercise program. Of course, choosing healthful fats is always recommended for long-term health benefits.

The literature indicates that appropriate nutrition aids muscle growth, recovery, and development. Periodization-supportive nutrition, or nutrient periodization, makes intuitive and research-backed sense and is a very creative and innovative approach to training.

References:

American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada (2000). Joint Position Statement: Nutrition and athletic performance. Medicine and Science in Sports and Exercise. 32:2130-2145.

Burke, L.M., Kiens, B., & Ivy, J.L. (2004). Carbohydrates and fat for training and recovery. Journal of Sports Science. 22, 15-30.

Coyle, E.F. (2004). The highs and lows of carbohydrate diets. Sports Science Exchange. 93(17): #2

Dreon D.M., Fernstrom H.A., Williams P.T., & Krauss R.M. (1999). A very low-fat diet is not associated with improved lipoprotein profiles in men with a predominance of large low-density lipoproteins. American Journal of Clinical Nutrition. 69, 411-418.

Fleck, S.J. (1999). Periodized strength training: A critical review. Journal of Strength and Conditioning Research. 13, 82-89.

Gibala, M.J. (2004). The role of protein in promoting recovery from exercise. Gatorade Sports Science Institute Sports Science News.

Hawley J.A., Dennis S.C., Lindsay F.H., & Noakes T.D. (1995). Nutritional practices of athletes: are they suboptimal? Journal of Sport Sciences. 13, S75-S87.


Lambert C.P., Frank L.L., & Evan W.J. (2004). Macronutrient considerations for the sport of bodybuilding. Sports Medicine. 34(5), 317-327.

Marx, J.O., Ratamess, N.A., Nindl, B.C., Gotshalk, L.A., Volek, J.S., Dohi, K., Bush, J.A., Gomez, A.L., Mazzetti, S.A., Fleck, S.J. Hakkinen, K., Newton, R.U. & Kraemer, W.J. (2001). Low-volume circuit versus high-volume periodized resistance training in women. Medicine & Science Sports & Exercise. 33 (4), 635-643.

Manore, M., Thompson, J. (2000). Sport nutrition for health and performance. Human Kinetics.

Manore M., Thompson J, & Russo, M. (1993). Diet and exercise strategies of a world-class bodybuilder. International Journal of Sports Nutrition. 3, 76-86.

Miller S.L., Tipton K.D., Chinkes D.L., Wolf S.E., & Wolfe R.R. (2003). Independent and combined effects of amino acids and glucose after resistance exercise. Medicine and Science in Sports and Exercise. 35, 449-455.

Sherman W.M. (1995). Metabolism of sugar and physical performance. American Journal of Clinical Nutrition. 62 (suppl.), 228S-241S.

U.S. Department of Health and Human Services (HHS) and the U.S. Department of Agriculture (USDA) 2005. Dietary Guidelines for Americans 2005. www.healthierus.gov/dietaryguidelines

National Academic of Sciences. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. September 5, 2002. Available at: http://www.iom.edu/Object.File/Master/4/154/0.pdf

Overturf, R. & Kravitz, L. (2002). Circuit training vs periodized resistance training in women. IDEA Personal Trainer 13(10), 28-33.

Tesch, P.A., Ploutz-Snyder, L.L, Ystrom, L., Castro, M.J., & Dudley, G.A. (1998). Skeletal muscle glycogen loss evoked by resistance exercise. Journal of Strength and Conditioning Research. 12, 67-73.

Tipton K.D., Wolfe R.R. (2004) Protein and amino acids for athletes. Journal of Sports
Sciences. 22, 65-79.

Venkatraman JT, Pendergast DR. (2002) Effect of Dietary Intake on Immune Function in Athletes. Sports Medicine. 32(5):323-37.


Tuesday
Jul262011

The Optimum Composition for Endurance Sports Drinks

By: Will G Hopkins, Matthew R Wood.
Site Link: Sports Science.

Sportscience 10, 59-62, 2006 & Sport and Recreation, AUT University, Auckland 0627, New Zealand.

Sports drinks aimed at enhancing endurance performance lasting several hours need to contain ~20 mM salt (sodium chloride) and ~10% carbohydrate in the form of glucose polymers and fructose. The salt and carbohydrate offset the losses of these substances caused by exercise. They also accelerate the uptake of water. Glucose polymers are used instead of glucose to keep the total osmotically active solute concentration (tonicity or osmolarity) of the drink below that of body fluids, because higher concentrations reduce the rate of emptying of the stomach and reduce the rate of uptake of water in the small intestine. KEYWORDS: carbohydrate, energy, hydration, nutrition, salt, water.

This article is an edited version of a literature review commissioned by a drink manufacturer on "the mechanisms… of water uptake in sports drinks of varying carbohydrate content and tonicity… Please explain how carbohydrates, electrolytes and tonicity affect water uptake and hydration in plain English." In our report we placed as much emphasis on the uptake of carbohydrate as of water, for the following reasons. First, in all but the hottest and most humid environments, exercise of duration and intensity sufficient to make dehydration an issue will also make supply of carbohydrate an issue. Secondly, getting the carbohydrate in is more of a challenge than getting the water in. Finally, we assumed that the drink is aimed at optimizing performance of elite endurance athletes and recreational multisport or ultraendurance athletes in competitions. For the mass market of less serious fitness enthusiasts, there is little need to worry about depletion of water, salt and carbohydrate during exercise. Indeed, fitness exercises can be performed without any concern for fluid and carbohydrate uptake.

We performed several searches with SportDiscus and Medline, but we got the best references by using Web of Science to find all the papers that cited a definitive paper by Rehrer et al. (1992). We found reviews by all the major researchers in the field (Brouns and Kovacs, 1997; Coyle, 2004; Jeukendrup, 2004; Jeukendrup et al., 2005; Maughan and Leiper, 1999; Rehrer, 2001).

There has been general agreement for the last decade that sports drinks need to contain salt (sodium chloride, NaCl) and carbohydrate (sugars) at concentrations of around 20 mM and 6% (6 g per 100 ml) respectively. The researchers also agree that at least some of the carbohydrate needs to be in the form or disaccharides (usually sucrose) or glucose polymers (maltodextrins). In the last year or two Jeukendrup and colleagues have found a way to increase the rate of absorption of carbohydrate. This report is mainly a review of the reviews. The only original-research papers we read were the recent ones not covered by the reviews.

The issues with sports-drink composition are as follows: 

Exercise Depletes Water and Salt

Exercise results in loss of water and salt from the body via evaporation of water from the lungs and sweating of water and salt from the skin. For exercise of sufficient duration and intensity, the losses reduce the volume of blood available for the heart to pump to the muscles and skin. Reduction of blood flow to muscles implies less delivery of oxygen to the muscles, so endurance performance declines. Reduction of blood flow to the skin implies less elimination of heat from the body, so the risk of heart stroke (damage to cells and tissues from overheating) increases, especially in a hot or humid environment. The loss of water and salt may also reduce production of sweat, which will also increase the risk of heat stroke. These effects become substantial for near-maximal exercise lasting an hour in a hot humid environment and two hours in a cool environment.

In long hard events with excessive sweating, failure to replace the salt lost in sweat, combined with excessive consumption of water or drinks containing no salt, increases the risk of hyponatremia. In hyponatremia the blood becomes more dilute, and as a consequence excess water enters all cells and tissues in the body, including the brain. The brain therefore swells, and because it is encased almost completely by the skull, pressure builds up inside the skull and can reduce the flow of blood to the brain. On very rare occasions brain damage and death ensue. 

Exercise Depletes Carbohydrate

Exercise results in loss of carbohydrate stored as glycogen in muscles and liver. After an hour of hard exercise, the loss contributes to the feeling of fatigue, either because the brain is affected by a fall in blood glucose concentration (via inability of the liver to maintain the concentration in the face of demand for glucose by muscle) or because the depletion of glycogen stored in muscle reduces the ability of muscle to do work. Performance therefore declines.

Drinks Can Offset These Depletions

Drinks containing appropriate concentration of salt and appropriate types and concentrations of carbohydrate consumed at an appropriate rate can offset the losses when consumed before and during exercise and can therefore enhance performance.

Research on what is appropriate is based on measurement of several variables: rate of emptying of the stomach, rate of uptake across the small intestine, rate of oxidation of ingested carbohydrate, and endurance performance.

Salt and carbohydrate in a sports drink act synergistically to stimulate the uptake of water. That is, the uptake of water is more rapid than occurs with pure water, with water plus salt, or with water plus carbohydrate, even though the concentration gradient for absorption of water in the small intestine is reduced by adding salt and carbohydrate to the drink. The mechanism of the synergistic effect presumably involves opening of water channels in the wall of the small intestine.

A sports drink can obviously speed full recovery of the losses post exercise. Fast recovery is an issue for athletes training hard every day, especially if they train twice a day.

Nevertheless, it may be beneficial to perform some training sessions in a somewhat dehydrated state and/or to delay restoration of fluid after training. The body may then supercompensate by increasing blood volume above normal, which would benefit endurance performance. It may also be beneficial for longer endurance and ultraendurance athletes to perform some training sessions in a state of depleted carbohydrate stores, to produce supercompensation of those stores and/or to switch the body to greater use of fat rather than carbohydrate in such events. Research on this question is in progress in several laboratories.

With these issues in mind, we made the following recommendations for the optimum composition of a sport drink for use by endurance athletes in competitions lasting several hours.

The concentration of salt is determined partly by the need to meet at least partly the expected rate of loss of salt in sweat.

The concentration of carbohydrate is determined partly by the maximum rate of absorption from the gut. (The maximum rate that carbohydrate can be used to fuel exercise by aerobic and anaerobic processes is greater than the rate it can be absorbed.)

The combined concentration of salt and carbohydrate is determined by the rate at which water needs to be consumed to replace losses, and the need to limit the inhibiting effect of high solute concentrations both on emptying of the stomach and on transport of water across the wall of the small intestine.

All of the above are determined partly by the duration and intensity of the exercise and by the environmental conditions in which it is performed.

A diagram summarizing the recent state of the art for exercise of durations up to 24 hours can be found in Rehrer (2001). She opted for 20 mM (1.2 g/L or 0.12% w/v) NaCl and 60 g/L (6% w/v) carbohydrate at least partly in the form of glucose polymers for an expected consumption rate of 1.5 L/h in exercise lasting 2 hours, through to twice as much NaCl and half as much carbohydrate for half the expected rate of fluid intake in exercise lasting 24 hours.

Recent research by Jeukendrup and colleagues indicates that the rate of absorption and oxidation of carbohydrate can be increased by using several kinds of carbohydrate, apparently because the rate of absorption of each kind of carbohydrate is limited by specific carriers in the wall of the small intestine.

With glucose or glucose polymers alone, the maximum rate is ~1.0 g/min, but Jentjens et al. (2004) achieved a rate of 1.7 g/min when their subjects ingested a mixture of glucose+fructose+sucrose at the rate of 1.2+0.6+0.6 g/min, in a drink containing 20 mM NaCl. After an initial bolus of 600 ml, the drink was consumed at a rate of 600 ml/h. We have calculated that the drink was therefore 12% glucose, 6% fructose, and 6% sucrose, which is 4× the usual recommended total concentration of carbohydrate. We have also calculated that the osmolarity of the drink was 1215 mOsm, which is more than 4× the concentration of body fluids. There was no indication of the effects of this drink on water absorption, but presumably it was strongly impaired.

In a more recent study, Wallis et al. (2005) achieved a rate of absorption/oxidation of carbohydrate of 1.5 g/min with a more realistic drink consisting of 7.5% maltodextrins and 3.75% fructose (total carbohydrate 11.25%). After an initial bolus of 600 ml, the drink was consumed at 800 ml/h. There was no NaCl in this drink, and the osmolarity was 260 mOsm. Rate of water absorption was not reported. Addition of 20 mM NaCl to this drink would presumably increase the rate of water absorption and probably also the rate of carbohydrate absorption. A reduction in the carbohydrate content would probably accelerate water uptake at the expense of reducing carbohydrate uptake slightly.

Use of a highly branched glucose polymer with a high molecular weight can reduce the solute concentration and accelerate emptying of the stomach. A drink containing 10% of this polymer had a total solute concentration of 150 mOsm and emptied from the stomach more rapidly than a drink containing 10% of the usual maltodextrins with a concentration of 270 mOsm (Takii et al., 2005). Effects on absorption/oxidation of carbohydrate were not reported.

Research on the composition of sports drinks will presumably continue for several years yet. In the meantime we would opt for a drink containing ~20 mM NaCl and ~10% carbohydrate in the form of the usual maltodextrins (6.5%) and fructose (3.5%). It would also be worth trialing a drink containing 11% of the glucose polymer of Takii et al. (2005) along with 4% fructose and 20 mM NaCl.

In conclusion, we emphasize that our recommendations apply to use of a drink in endurance competitions, not in training for such competitions. The optimal composition of a drink for training will depend on various factors, including whether it is consumed before, during or after training, what kind of training session is undertaken, and in what training phase the session occurs. On occasions the best drink may contain protein, amino acids, carbohydrate, or only water. Sometimes no drink might be the best strategy.

References

Brouns F, Kovacs E (1997). Functional drinks for athletes. Trends in Food Science & Technology 8, 414-421

Coyle EF (2004). Fluid and fuel intake during exercise. Journal of Sports Sciences 22, 39-55

Jentjens R, Moseley L, Waring RH, Harding LK, Jeukendrup AE (2004). Oxidation of combined ingestion of glucose and fructose during exercise. Journal of Applied Physiology 96, 1277-1284

Jeukendrup AE (2004). Carbohydrate intake during exercise and performance. Nutrition 20, 669-677

Jeukendrup AE, Jentjens RLPG, Moseley L (2005). Nutritional considerations in triathlon. Sports Medicine 35, 163-181

Maughan RJ, Leiper JB (1999). Limitations to fluid replacement during exercise. Canadian Journal of Applied Physiology-Revue Canadienne De Physiologie Appliquee 24, 173-187

Rehrer NJ, Wagenmakers AJM, Beckers EJ, Halliday D, Leiiper JB, Brouns F, Maughan RJ, Westerterp K, Saris WH (1992). Gastric emptying, absorption, and carbohydrate oxidation during prolonged exercise. Journal of Applied Physiology 72, 468-475

Rehrer NJ (2001). Fluid and electrolyte balance in ultra-endurance sport. Sports Medicine 31, 701-715

Takii H, Takii NY, Kometani T, Nishimura T, Nakae T, Kuriki T, Fushiki T (2005). Fluids containing a highly branched cyclic dextrin influence the gastric emptying rate. International Journal of Sports Medicine 26, 314-319

Wallis GA, Rowlands DS, Shaw C, Jentjens R, Jeukendrup AE (2005). Oxidation of combined ingestion of maltodextrins and fructose during exercise. Medicine and Science in Sports and Exercise 37, 426-432

Tuesday
Jul262011

Carbohydrate Intake Targets for Athletes: Grams or Percent?

By:Louise Burke: Australian Institute of Sport, Canberra.
Site Link: Sports Science.
Article Link: Carbohydrate Intake Targets for Athletes: Grams or Percent?: Jul-Aug 98

How to fine tune dietary energy requirements

Using different terminology to educate athletes about their carbohydrate intake goals interferes at times with the interpretation of studies on carbohydrate and sports performance, and may cause athletes to have their diets unfairly criticized. Nutrition guidelines for the community express carbohydrate intake goals in terms of the percentage of energy that should be consumed from carbohydrate. This works because the message is general and the emphasis is on a relative change in fat and carbohydrate consumption. When the muscle fuel needs of an athlete are moderate, adequate carbohydrate intake should be provided by a diet that meets these guidelines for healthy eating. In most Western countries this message is to increase carbohydrate intake to at least 50-55% of energy.

However, in situations where maximal glycogen storage is desirable and/or the athlete must meet the fuel bill of prolonged exercise sessions, carbohydrate needs become more specific. In these cases, the muscle has an absolute requirement for carbohydrate (see Table below). Therefore, it is preferable to set definite carbohydrate intake goals for athletes, scaled to take the size of the muscle mass into account (i.e., the athlete's body mass). The guideline to consume 7-10 grams of carbohydrate per kilogram body mass is not only considerate of the muscles needs, but is also user-friendly. It is relatively easy to use a ready reckoner of the carbohydrate content of foods to add up the fuel provided by a meal or a diet - for example, to reach a target amount of 50 g snack after training, or a daily intake of 400-600 g. It takes far more nutritional expertise to imagine what a dietary ratio of 50% or 60% or 70% carbohydrate looks like on a plate. With the advice of a sports dietitian, an athlete should be able to narrow their carbohydrate intake targets to specific levels for specific occasions.

The absolute amount of carbohydrate required for optimal glycogen synthesis is greater than the typical intakes of most people, including athletes. And it may require an athlete not only to eat more carbohydrate (in grams), but to devote more of their total energy intake to fuel foods to do so. Typically, athletes need to earmark 50-70% of their energy intake to meet their carbohydrate needs. This is a wide range, because in real life the total energy needs and the muscle fuel needs of an athlete are not always synchronized. The "perfect" carbohydrate:energy ratio cannot be fixed. Athletes who have large muscle mass and heavy training programs usually have very high energy requirements. For these athletes, total intakes of 800-1000 grams of carbohydrate representing 8-10 grams per kilogram of body mass may be consumed from only 45% of their energy budget. Other athletes may need to devote 70% of a restricted energy budget to achieve a carbohydrate intake of even 6-7 grams per kilogram. This situation is particularly common in female athletes and others whose main dietary concern is to maintain lower body fat levels than seems natural.

There is an unfortunate tendency of those working with athletes to regard carbohydrate intake guidelines as rigid. Many judge the fuel intake of an athlete or a group of athletes to be deficient or inadequate based on the percentage of energy derived from carbohydrate. Some sports nutrition guidelines, even from recognized bodies such as the American Dietetic Association, maintain the confusion because they set their dietary guidelines for athletes based on energy ratios. However this is inappropriate if the goal is to judge fuel intake, and this doesn't track closely with total energy needs. In the first situation described above, an athlete might be consuming a high total intake of carbohydrate, adequate to meet their fuel requirements. However, they will be judged to be following a low- or moderate-carbohydrate diet from the perspective of energy ratio. This often happens in the assessment of the diets of individual athletes, but has also led to some questionable interpretations of research data. Some studies have exposed athletes to so-called high or moderate (low) carbohydrate diets and compared metabolic and performance outcomes. They have found no differences between responses to the diets and concluded that high carbohydrate diets are not important for athletes. However, their moderate carbohydrate diets (40% carbohydrate) may have provided reasonably large amounts of carbohydrate, thanks to a high total energy intake. So, even the moderate carbohydrate diet met the fuel needs of the athlete. A high carbohydrate diet (80% of energy) may be superfluous for this group.

Although total amounts of carbohydrate may be a better guide for assessing or setting goals for an athlete, they still must be regarded with some flexibility. In all areas of nutrition, judgments of adequacy or deficiency cannot be made from a single piece of evidence, particularly when it comes from a food record or another dietary survey tool. Dietary survey methods suffer from many errors of reliability and validity which generally lead to an underestimation of true dietary intake.

A judgment of adequate or inadequate carbohydrate intake in an individual athlete can only be made by assessing overall nutritional goals and nutrient needs from a number of sources of information. Specific information about an individual's training load and ability to recover between sessions may help to fine tune carbohydrate intake targets. It is important, particularly in terms of judging everyday carbohydrate intake, to regard guidelines as an approximation rather than a fixed rule. For athletes who have important or increased carbohydrate needs, it is both more reliable and more practical to set guidelines in terms of a fixed amount of carbohydrate, rather an energy percentage.

Summary of carbohydrate intake goals for the athlete

Goal

Carbohydrate Intake Target

5-6 hours of moderate intensity exercise, extremely prolonged and intense exercise. Very high total energy requirements, daily muscle glycogen recovery, and continued refueling during exercise. (Tour de France cyclists)

10-12+ g/kg daily

To maximize daily muscle glycogen recovery in order to enhance prolonged daily training, or "load" the muscle with glycogen before a prolonged exercise competition

7-10g/kg daily

To meet fuel needs and general nutrition goals in a less fuel-demanding program - for example, < 1 hr of moderate intensity exercise, or many hours of predominantly low intensity exercise.

5-7 g/kg daily

To enhance early recovery after exercise, when the next session is less than 8 hrs away and glycogen recovery may be limiting.

1g/kg+ soon after exercise, and continued intake over next hours so that a total of ~1g/kg/2hrs is achieved in snacks or a large meal.

To enhance fuel availability for a prolonged exercise session (1 hr or longer)

1-4 g/kg during the 1-4 hours pre-exercise.

To provide an additional source of carbohydrate during prolonged moderate and high intensity exercise, particularly in hot conditions or where pre-exercise fuel stores are sub optimal.

30-60 g/hr in an appropriate fluid or food form

  

References

Hawley, J.A. and Burke, L.M. (1998). Peak Performance: Training and Nutritional Strategies for Sport. Sydney: Allen and Unwin.

Tuesday
Jul262011

Endurance Performers and Iron-Deficiency

By: Karoly Piko.
Chief Physician at the Department of Emergency Medicine
Site Link: Coachr.

Karoly, Piko M.D.: Chief Physician at the Department of Emergency Medicine, Joso Andros County Hospital, President of the Hungarian Association of Emergency Medicine since 1995, Head Physician of the Hungarian National Olympic and Track and Field teams since 1980. Votfous publications in the fields of emergency medicine and sport injuries.

Endurance performers are susceptible to iron-deficiency because the absorption of iron cannot balance the losses incurred through training. Therefore, a preventive daily dose of 105 mg of ferrous sulphate is necessary, especially for young women. The symptoms of iron-deficiency often remain undiscovered. The haematological parameters of training iron-deficient and anaemic women improve when a daily 210mg ferrous sulphate dose is applied. In endurance performers the effects of iron-deficiency on the synthesis of neurotransmitters, cognitive function, mitochondrial function and protein metabolism remain topics for future research studies.

A large number of sports medicine studies have looked at iron-deficiency anemia in athletes. Many of them have proved the role of iron in blood synthesis, in the activation of enzymes necessary for synthesis, the catabolism and function of neurotransmitters (dopamine, serotonin and noradrenalin); and in the regeneration of cells. Table 1 summarizes the symptoms of iron-deficiency and it is important to emphasize that the symptoms are not due to anemia.

Some of the literature argues that performers---especially endurance athletes---are mildly iron-deficient, which places limits on their performance potential. In other research the contrary finding was put forward so the role of iron substitution and preventive iron therapy is often contested.

The author has examined iron-deficient, iron-deficient anaemic and non-iron deficient endurance athletes and also reviewed the recent related literature and compared it with other findings. 

Methods 

Endurance performers from athletics and triathlon were examined. In the morning pre-prandial blood sample haematological parameters were examined (ferritin, haemoglobin, transferrin, red blood cell volume and iron levels). The participants were divided into three groups:

a. The first group consisted of male and female athletes, who received no iron preparations.

b. In the second group participants received 105mg of ferrous sulphate daily.

c. In the third group known iron-deficient, anaemic female athletes were studied.

In each group the mathematical average of every parameter was determined. After twelve weeks of training the laboratory studies were repeated.

Results

Figure 1 summarizes the development of laboratory parameters in fifteen male athletes (mean age 18 years), who did not receive iron therapy. In these cases anaemic did not develop, in two cases latently deficient iron levels were noticed. In this group the author observed a tendency towards low iron levels.

 

Figure 2 shows the parameters of fifteen female athletes (mean age 20.2 years), who did not receive iron therapy. In six cases iron-deficiency and, in two cases, iron-deficiency anaemic was observed.

 

Figure 3 shows the parameters of 20 male competitors (mean age 21.2 years), who received 105mg ferrous sulphate daily during the period of training. After three months neither iron-deficiency, nor iron- deficiency anaemia developed.

Figure 4 shows the parameters of long distance running and triathlon female athletes who received 105mg daily doses of iron sulphate.

Figure 5 reviews the haematological parameters of 8 female competitors (mean age 20.5 years), known to have iron-deficiency anaemia, who received 210mg ferrous sulphate daily. Our results show that, in spite of training, the propensity for iron-deficiency and anaemia decreased.

Discussion

For decades many studies have looked at the role of iron-deficiency and its effects on performance. Iron absorption and loss should reflect a dynamic equilibrium (Fig. 6.). In the case of sports performers loss of iron is increased by many factors such as perspiration, gastrointestinal and urogenital bleeding during training, and inefficient iron intake. The so-called "runner anaemia" is the result of the increased fragility of the red blood cells, according to some experts. Other studies question that theory by illustrating the similar haematological levels found in swimmers. 

The factors above are especially important in endurance athletes. It is evident that, in the case of iron-deficiency, the organism tries to compensate by increasing the absorption of iron. It is not clear however, whether the organism can maintain the new equilibrium.

The symptoms of iron-deficiency should be separated from those of anaemia. Because they appear long before anaemia is evident and so remain unrecognized. (see Table I.); the symptoms of the patient are often regarded as a result of increased training.

In spite of the fact that there is controversy over the relationship between iron-deficiency and diminished performance (in mild iron-deficiency no deterioration in performance was noticed), it is difficult to imagine that low iron induced neurotransmitter dysfunction would not negatively influence CNS function or even dysfunction of myogen cell metabolism, both leading to a reduced ability to perform.
It seems that in the case of endurance sports preventive iron supplementation is necessary, because our organism cannot cope with the increased loss of iron. There is no need to fear an overdose of iron, because only the required amount of Iron is absorbed, the rest is eliminated in faeces.

Conclusion

  1. The studies of iron metabolism in endurance athletes reveal the following:
  2. In endurance athletes iron-deficiency is common and anaemia is often observed.
  3. The haemostatus of these athletes should be monitored at least every three months.
  4. A preventive daily intake of 10Smg ferrous sulphate seems to be necessary; over dosage was not observed.
  5. A therapeutic dosage (210mg/day) improved the haemostatic parameters in spite of training. There was no need for intravenous application.

The effect of iron on cognitive functions, neurotransmitter synthesis, protein metabolism and the metabolism within the mitochondria needs future evaluation.

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