Entries in Hydration (9)

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.

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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.

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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.

36. Zembrzuski CD. A three-dimensional approach to hydration of elders: Administration, clinical staff, and in-service education. Geriatr Nurs 18: 2, 1997.


 

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.

 

 

Tuesday
Dec062011

Exercise Science and Coaching: Correcting Common Misunderstandings About Endurance Exercise

By: Andrew N. Bosch, PhD
UCT/ MRC Research Unit for Exercise Science and Sports Medicine.
Department of Human Biology, University of Cape Town and Sports Science Institute of South Africa
From: International Journal of Sports Science & Coaching Volume 1 • Number 1 • 2006


Many coaches who work with endurance athletes still believe in old concepts that can no longer be considered correct. Prime amongst these are the understanding, or misunderstanding, of the concepts of maximal oxygen uptake (VO2 max), lactate threshold, training heart rate, and dehydration and fluid requirements during prolonged exercise.

Knowing the VO2 max of an athlete is not particularly useful to the coach, and the exact VO2 max value of any particular athlete can vary considerably as fitness changes. Race performance is a more useful measure on which to base training schedules.

Lactic acid production, far from being an undesirable event, is of great importance and is actually beneficial to the athlete. The lactate concentration during exercise, and the lactate turnpoint, are both widely measured. The nature of the information that these measures can provide about training and training status, however, is still based on information from the 1980s, although more current information is available and many of the original concepts have been modified.

Heart rate is often used to prescribe training intensity, but it is important to understand the limitations inherent in its use. If used correctly, it is a useful tool for the coach.
Similarly, many athletes and coaches still believe that it is necessary to maintain a high fluid intake to avoid dehydration and prevent associated collapse. These beliefs are incorrect, but modern exercise science has been able to advance the knowledge in this area and provide more accurate information.
Exercise science continues to progress and can offer much to the coach willing to accept new and changing ideas.

Key words: Anaerobic threshold; Endurance training; hydration; lactic acid; maximal oxygen uptake; training heart rate

Introduction

Sports science knowledge has progressed tremendously in the last 20 years in terms of the understanding of many of the underlying concepts in exercise physiology and human performance. Many coaches, however, have failed to take cognisance of the new information and still believe in old and out-dated concepts, many of which frankly are wrong. And it is this incorrect understanding that is then applied to the coaching of athletes. In the following article, some of these misconceptions related to endurance performance are highlighted, specifically those around maximal oxygen uptake (VO2 max), lactate threshold, training heart rate, dehydration, and fluid requirements during prolonged exercise. Although runners are most often referred to in the discussion that follows, the principles are applicable to all genre of endurance athlete.

VO2 Max

Every so often a request is received from the coach of a runner or cyclist wanting to know ifit would be possible to measure the VO2 max of one of their athletes. I explain that it is, indeed, possible, but then go on to ask why they want to have the VO2 max of the athlete measured? There is usually one of two replies. Firstly, I am told, by knowing his or her VO2 max the runner will know the esoteric time that he or she is ultimately capable of running for some particular race distance, and therefore their ultimate potential as a runner. Secondly, once their VO2 max is known it will be possible to prescribe the ultimate personalised training schedule. Unfortunately, knowing the VO2 max of a runner does not answer either question.

It is widely believed by those involved in endurance sports that the VO2 max is genetically determined and never changes, and that an individual is born with either a high or low VO2 max. Generally, someone with a high VO2 max value is considered to have a cardiovascular system capable of delivering large amounts of oxygen to the working muscle and is able to exercise at a maximum aerobic work output that is determined by the exercise intensity that can be sustained by this supply of oxygen [1]. In this paradigm it does not appear to matter whether a runner or cyclist is unfit or superbly fit, the VO2 max value obtained in a test is theoretically the same. However, it is intuitively obvious that when fit, the athlete can run much faster on the treadmill than when unfit. Thus, since VO2 max is genetically determined and does not change, VO2 max would be reached at a relatively slow running speed when a runner is unfit compared to when very fit, when a much higher speed or workload can be reached. This means that in a totally unfit world class runner we would measure a high VO2 max (for example, 75 ml/kg/min or higher, a reasonable VO2 max value for an elite runner) at a speed of maybe 17 km/hr in a testing protocol in which the treadmill remains flat during the test. When very fit the same athlete will reach the same VO2 max, but now the speed reached on the treadmill will be around 24 km/hr (a reasonable speed for an elite athlete in such a test). The problem is that such a high VO2 max is never measured at a speed of just 17 km/hr, or thereabout. This would be almost impossibly inefficient [2]. The theory of a genetically set and unchanging VO2 max, regardless of work output therefore begins to appear a little shaky.

This concept of VO2 max evolved originally from misinterpretation of the data of early experimental work [1; 3-5]. It was believed that as an athlete ran faster and faster during a treadmill test, an increasing volume of oxygen was needed by the muscles, a process which continued until the supply of oxygen became limiting, or the ability of the muscle to utilise oxygen was exceeded. At this point there would be no further increase in oxygen uptake, despite further increases in running speed [1]. The plateau in oxygen utilisation was regarded as the VO2 max of the runner. If high, then the athlete had great genetic potential. This has been termed the cardiovascular/ anaerobic model by Noakes [1] and needs revision, although others adhere to the concept [6]. However, 30% of all runners and cyclists tested in exercise laboratories never show a plateau in their oxygen uptake [4; 7]. Instead, the oxygen uptake is still increasing when the athlete cannot continue the test. The conventional view of VO2 max now appears to be even more suspect.

Consider a different possibility. The muscles of a runner require a certain amount of oxygen to sustain contraction at a given speed. When the speed is increased, the muscles have to work harder and there is therefore a corresponding increase in the volume of oxygen needed to run at the higher speed. As the runner runs faster and faster, it follows that there is a concomitant increase in the oxygen required, until ultimately something other than oxygen supply to the muscle prevents the muscle from being able to work harder and to sustain a further increase in running speed.

The brain may be the ultimate subconscious controller, by sensing a pending limitation in the maximum capacity of the coronary blood flow to supply oxygen to the heart as exercise intensity increases, and then preventing a further increase in muscle contractility to prevent damage to the heart during maximal exercise [1].

The volume of oxygen being used by the muscle when maximum running speed has been reached is termed the VO2 max. With this theory, the increase in oxygen requirement merely tracks the increase in running speed, until a peak running speed and therefore peak oxygen requirement (VO2 max) is attained. It is easy to see why the VO2 max value will change (which it does) as a runner gets fitter and becomes capable of running faster. Within this framework, the genetically determined limit of VO2 max is actually determined by the highest running speed that the contractility of the muscles can sustain [8] before the brain limits performance to protect the heart, as described above [1]. Of practical importance, is that the exercise scientist and coach cannot use the VO2 max test as a predictor of future performance in someone who still has the capacity to improve their running by utilising a scientifically designed training programme. A great training-induced increase in running speed will result in a substantial change in VO2 max. Only when widely disparate groups of athletes are tested can a VO2 max value be used to distinguish between athletes (i.e. very fast and very slow [2; 9; 10]). In a group of athletes with similar ability, the VO2 max value cannot distinguish between the faster and slower runners i.e. their race performance. Neither is the knowledge of a VO2 max value going to assist in the construction of a training programme, other than by indirectly giving an indication of the time in which a race may currently be completed, by the use of various tables that are available [11]. Indeed, current race performance provides the most useful information for the coach on which to base training prescription [11].

There are, however, some potential uses of a VO2 max test for a coach. When constructing a training programme for someone who has not run any races and who therefore has no race times from which to determine current ability, a VO2 max test will help by giving an indication of the current capability of the athlete on which to base training schedules. If done at regular intervals, the test can provide information about the efficacy of a training programme [11] as laboratory conditions are very reproducible with regard to temperature and absence of wind. However, the peak speed attained in the test is probably the best indicator of current ability [1; 12-14] and not the actual VO2 max value. Race times remain the most useful measure on which to prescribe running speed in training schedules [11].

Lactic Acid

Most athletes and coaches still believe that lactic acid is released during hard or unaccustomed exercise and that this is what limits performance, as well as being the cause of stiffness. Neither is correct. Furthermore, the terminology “lactic acid,” is not correct.

Lactic acid does not exist as such in the body - it exists as lactate at physiological pH [15], and it is this that is actually measured in the blood when “lactic acid” concentration is measured, as is done when a “lactate threshold” is determined in an athlete. This distinction is important not only for the sake of correctness, but more importantly, because lactate and lactic acid would have different physiological effects.

The first misconception is that lactic acid is the cause of the stiffness felt after an event such as a marathon. Stiffness is due to damage to the muscle [1], and not an accumulation of lactic acid crystals in the muscle [1; 16], as is commonly believed.

The second misconception is that lactate is responsible for acidifying the blood, thereby causing fatigue. To the contrary, the production of lactate is actually important for two reasons. Firstly, when lactate is produced from pyruvate in the muscle, a hydrogen ion is “consumed” in the process [15]. Consequently the production of lactate actually reduces the acidity in the muscle cells and is thus a beneficial process. Secondly, lactate is an important fuel that is used by the muscles during prolonged exercise [17; 18]. It can be produced in one muscle cell and utilized as a fuel in another, or it can be released from the muscle and converted in the liver to glucose, which is then used as an energy source. So rather than cause fatigue, lactate production actually helps to delay fatigue [19].

Anaerobic Threshold

Closely allied to the thinking that lactate production is bad for performance, is the concept of measuring the blood lactate concentration to determine the so-called “anaerobic threshold” or “lactate threshold.”. The origin of this belief can probably be traced to the early studies of Fletcher and Hopkins [20]. Thus we see photographs of athletes at the track or at the side of the pool having a blood sample taken, with an accompanying caption indicating that the workout is being monitored by measuring “lactic acid.” The supposed rationale is that as speed is increased, a point is reached at which there is insufficient oxygen available to the muscle and energy sources that do not require oxygen (oxygen independent pathways, previously termed the anaerobic energy system) then contribute to the energy that is needed. This supposedly results in a disproportionate increase in the blood lactate concentration, a point identified as the “anaerobic” or “oxygen deficient” threshold. This is also known as the lactate threshold or lactate turnpoint.

There are two problems with this concept. First of all, the muscle never becomes anaerobic; there are other reasons for the increase that is measured in blood lactate concentration [21]. Secondly, the so-called disproportionate increase causing a turnpoint is not correct, in that the increase is actually exponential [22-24]. This is seen when many samples are taken, as in the exercise laboratory, where a blood sample can be drawn every 30 seconds as an athlete runs faster and faster.

Although a graph showing a “breakpoint” in lactate concentration as speed increases cannot be drawn as the breakpoint does not exist, a graph can nevertheless be drawn depicting the curvilinear increase in blood lactate concentration as running speed or exercise intensity increases. This curve changes in shape (shifts to the right) as fitness level changes. Particularly, the fitter a runner gets, the more the curve shifts to the right on the graph, meaning that at any given lactate concentration the running speed or work output is higher than before. A shift in the lactate curve to a higher workload or percentage VO2 max occurs due to a reduced rate of lactate production by the muscles and an increased ability of the body to clear the lactate produced [25; 26]. Often, the running speed at a lactate concentration of 4mmol/l is used as a standard for comparison. It is sometimes suggested that this can be used as a guide for training speed (i.e. a runner could do some runs each week at the speed corresponding to the 4mmol/l lactate concentration, some runs above this speed, and recovery runs at a lower speed). Of course, as fitness changes and the curve shifts, these speeds will change, and so a new curve will have to be determined. In concept this works well, but the problem is that neither exercise scientists nor coaches know how much running should be done below, at, and above the 4mmol/l concentration. The 4 mmol/l concentration referred to is a somewhat arbitrarily chosen concentration. It could just as well have been 3.5 mmol/l or 4.5 mmol/l, which would result in different training speeds for the athlete utilizing this system. Indeed, Borch et al [27] suggest 3 mmol/l as the lactate concentration representing an average steady state value. Measuring the maximal steady state lactate concentration may be useful, but requires 4-5 laboratory visits. Thus the real value in determining a ‘lactate curve’ is to monitor how it shifts with training. The desirable shift is one in which a faster running speed is achieved at the same lactate concentration. This regular testing can be done in the laboratory, with the athlete running on a treadmill or on a track, in which running speed can be carefully controlled, such as by means of pace lights.

Training Heart Rate

In recent years the concept of using heart rate while training as an indicator of the correct training intensity, has gained in popularity. Specifically, various heart rate “training zones” have been suggested, and ways to calculate these proposed. This approach has been described in many articles written for coaches and runners [27-29] and does have potential for being a precise way to regulate running intensity in training, particularly for novice runners. However, at present there are no scientific data to support an ideal specific heart rate for different types of training, and much of what is written is based on anecdotal experiences. There is no doubt that future studies will refine this area, making the prescription of training heart rate a more exact science.

Probably the greatest value in heart rate in training is for the coach to use it as a way of ensuring that an athlete does not train too hard on those days when nothing more than an easy training session is prescribed. The use of heart rate for more absolute prescription has the risk of the athlete training at the wrong intensity as a result of the large daily variability in heart rate due to influence of diurnal variation, temperature differences, sleep patterns, and stress [30]. All these can result in the prescribed training heart rate being either too high or too low on a given day. Thus the athlete may train too easily on one day, but on another day when more recovery is needed from a prior hard training session, the training intensity may be too high. The coach is probably better able to assess the most suitable intensity for the athlete. Nevertheless, training intensity based on heart rate may have some value [28].

The use of heart rate as a monitoring tool during training, as opposed to being used to dictate training intensity is a useful aid that coaches can use to assess the training response of an athlete. A progressive decline (over weeks) in heart rate for a given training session would indicate appropriate adaptive response by the athlete; a progressive increase in normal training heart rate would indicate a failure in the adaptive process and that the training load should be adjusted. Similarly, an abnormally high heart rate for a given training session may indicate approaching illness or failure to adapt to the training load and impending overtraining. The athlete would then be well-advised to train only lightly, or to rest [30].

Post-Run Stiffness

In the section on lactic acid, it was stated that the stiffness and muscle pain felt after a marathon or hard workout is not caused by lactic acid. While this was believed to be the case some decades ago, it is now known that lactic acid is not the cause of muscle stiffness, but is the result of damage to the muscle cells, connective tissue and contractile proteins [31-33].

Although the precise cause of delayed onset muscle soreness remains unknown, all runners and coaches are aware that the degree of pain depends on the intensity, duration and type of workout. For example, there is more muscle pain after a long or hard downhill run than after running over flat terrain (i.e. if eccentric muscle actions are emphasised [34]). In fact, it is this phenomenon that begins to exclude a build-up of lactic acid as a cause of the pain. In downhill running, the concentration of lactate in the blood and muscle will be low compared to running at the same speed on the flat. Thus, the most painful post-race stiffness can occur when the lactate concentration is lowest.

If a blood sample is taken from a runner the day after a marathon, especially an ultra- marathon, the concentration of an enzyme, creatine kinase, will be high [35-37]. This is an indication that muscle damage has occurred, as this particular enzyme “leaks” from damaged muscle. The “damage” referred to is minute tears or ruptures of the muscle fibres [38; 39]. This trauma to the muscle can be visualised if a sample of the muscle is examined microscopically. However, it is not just the muscle that is damaged. By measuring the amino acid hydroxyproline, it is possible to show that the connective tissue in and around the muscles is also disrupted [40]. What this shows is that stiffness results from muscle damage and breakdown of connective tissue.

Running fast or running downhill places greater strain on the muscle fibres and connective tissue compared with running on the flat. Downhill running is particularly damaging because of the greater eccentric muscle actions that occur. It is this simultaneous contracting of the muscle while being forced biomechanically to lengthen that is most damaging to muscle fibres.

What does this mean for the runner and coach? From a training and racing point of view, after the muscles have recovered from the damage that caused the stiffness and the adaptive process is complete, the muscle is more resistant to damage from subsequent exercise for up to six weeks [41]. From a coaching point of view, hard training sessions should be withheld when there is muscle pain, as further damage could result. It would be better to allow the appropriate physiological adaptations to take place before resuming hard training sessions. Weight training to increase the strength of the muscle [1] may be beneficial. It has been suggested that vitamin E may help to reduce muscle soreness, but there is little evidence to support this idea [42]. Vitamin E is thought to act as an antioxidant that may blunt the damaging action of free radicals, which attack the cell membrane of the muscle fibre.

It has also been suggested that stretching the painful muscle or muscles may be beneficial, but this has not consistently been shown to alleviate delayed onset muscle soreness. Neither is there any evidence that massage or ultrasound speed up recovery [43]. Similarly, an easy “loosening up” run “to flush out the lactic acid” is unlikely to speed up recovery, although it is also unlikely to result in further damage.

The real cause of muscle stiffness after a hard run is clearly not due to lactic acid in the muscle. Coaches will be in a better position to manage the return to normal training of their athletes after training or racing that has induced muscle soreness, if they understand the effects of type, intensity, and volume of training on muscle stiffness after exercise.

Dehydration, Heat Exhaustion and Heat Stroke

Historically, the understanding has been that runners collapse (most often at the end of races) due to dehydration. This is popularly thought to be more likely when the environmental temperature is high and dehydration more severe. “Heat exhaustion” has been incorrectly thought to be associated with dehydration, yet there is no evidence to support this [1]. “Heat stroke” is an entirely different condition, associated with an increase in body temperature.

There are a number of critical errors in the traditional thinking on the issue of dehydration. Firstly, and possibly most importantly, rectal temperatures are not abnormally elevated in collapsed runners suffering from “dehydration” [44; 45]. Secondly, there is no published evidence that runners with dehydration/ heat exhaustion will develop heat stroke if left untreated [46; 47]. And thirdly, the question must be asked why these runners nearly always collapse at the finish of the race and not during the race. Thus we must look for another explanation as to why the runners collapse.

The explanation is found in a condition called postural hypotension [44; 47-50]. While running, the high heart rate and rhythmic contraction of the leg muscles maintain blood pressure and aids in the return of blood from the legs. When running ceases, the pump action of the leg muscles stops and the heart rate drops rapidly. This results in pooling of the blood in the veins of the lower limb, which in turn causes blood pressure to decrease. It is the lowered blood pressure that results in collapse. Secondly, there is an increase in peripheral blood flow to regulate body temperature. This is more pronounced in hot conditions, and results in a reduction in the pressure of blood filling the heart [51]. Treatment is therefore very simple: If the runner lies down with the legs elevated, the return of blood from the legs is aided, blood pressure is restored and after a short while the runner will have recovered. Cooling the legs may be beneficial. As a preventive measure, it is a good idea to continue to walk after the finish line has been crossed. A second possibility is to lie down as soon as possible and elevate the legs slightly, with cooling of the legs as an additional option.

Heat exhaustion as a result of dehydration does not, therefore, exist and is not a condition that coaches need to be concerned about. This contrasts with heat stroke, in which the body temperature becomes very high (rectal temperature above 41°C) and is a potentially dangerous condition. Even after the athlete has stopped, either voluntarily or because of collapse, the temperature remains elevated because of physiological and biochemical abnormalities in the muscles. Thus the athlete must be cooled as quickly as possible, using methods such as fans, to bring the body temperature down to below 38 degrees Celsius.
Heat stroke develops as a result of a combination of a number of factors. Particularly, a high environmental temperature (>28°C) is more likely to result in the problem than when conditions are cooler. If the humidity is also high, there is an additional heat load on the runner because the sweating mechanism of the body is rendered ineffective. Sweat running off the body, as it does when the humidity is high, does not result in cooling. To cool the surface temperature of the skin, the sweat must evaporate. In addition, and also very importantly, the metabolic heat produced by the runner must be high. Thus, it is the faster athletes who are at risk, who are exercising at a high intensity. It is also, therefore, in races shorter than the marathon in which there is a high likelihood of heat stroke because of the much higher running intensity in shorter races such as cross country (on a hot day) or a 10 km race [46; 47; 52]. Thirdly, it appears that some runners are more susceptible to the development of heat stroke than others [53].

Contrary to popular belief, dehydration is not a major cause of the development of heat stroke. Although adequate fluid replacement during racing in the heat may reduce the risk of heat injury, it is not the only factor and may not even be the most important factor [46; 47; 54; 55]. Arunner can develop heat stroke without being dehydrated. Conversely, a runner can be dehydrated, but not develop heat stroke. If the recommended guidelines for fluid ingestion are followed (~600 ml/ hour), it is very unlikely that fluid deficit will play a role in the development of heat stroke.

Fluid Intake During Exercise

During events such as marathon running, one often reads recommendations suggesting that more than 1L of fluid should be ingested every hour. Ingestion of such a high volume is unnecessary, however, and probably impossible for faster runners to adhere to.

The rate at which fluid ingested during exercise empties from the stomach before being absorbed in the small intestine is influenced by a number of factors. These include the temperature of the fluid, the volume of fluid ingested, and the concentration of any carbohydrate such as glucose, fructose, sucrose or glucose polymer in the water. Thus it is important that athletes follow the correct regimen to ensure optimal fluid and carbohydrate replacement. This consists of ingesting 500-600 ml per hour of a fluid containing 7-10% carbohydrate [56]. This serves two purposes. It supplies a source of carbohydrate to maintain blood glucose concentration, as well as all the fluid replacement that is necessary during prolonged exercise, except possibly under extreme environmental conditions.

Ingestion of too much water during prolonged exercise is not only unnecessary, but can be harmful. In some susceptible people, ingesting large volumes of water can result in a condition called “water intoxication” or hyponatraemia. This occurs when the body’s normal sodium concentration becomes significantly diluted, because the amount of water or sports drink ingested is far in excess of what is needed during exercise to maintain hydration [46; 54; 57; 58]. As with heat stroke, in extreme cases this condition can be life threatening, in this case due to cerebral oedema.

Conclusions

VO2 max testing can be of some limited use to a coach when constructing a training programme for someone who has not run any races. If done regularly, the test can provide information about the efficacy of a training programme. However, the peak speed attained in the test is probably the best indicator of current ability, but race times are the most useful measure on which to prescribe running speed in training schedules.

Rather than cause fatigue, the process of lactate production helps to delay fatigue. In addition, it is important as a fuel substrate. The real value in determining a ‘lactate curve’ is to monitor how it shifts with training, the desirable shift being one in which a faster running speed is achieved at the same lactate concentration.

Heart rate during training is a useful monitoring tool, but should not be used to dictate training intensity. Rather, training heart rate information, together with knowledge of current race speeds and training-induced fatigue, should be used by the coach to determine training intensity. Ultimately, the influence of various parameters that effect heart rate response will be well researched and the coach will then be able to prescribe a specific heart rate for different types of training.

Muscle stiffness after a hard run is not due to lactic acid in the muscle. Return to normal training should be prescribed based on the knowledge that soreness is due to muscle damage.

Dehydration is not a major cause of the development of heat stroke. Heat stroke can occur without dehydration, and conversely, dehydration can occur without heat stroke. If the recommended guidelines for fluid ingestion are followed, it is very unlikely that fluid deficit will play a role in the development of heat stroke.

Ingestion of too much water during prolonged exercise is not only unnecessary, but can be harmful. In some susceptible people, ingesting large volumes of water can result in a condition called “water intoxication” or hyponatraemia.

Despite the exponential increase in knowledge in exercise physiology in the last two decades, the process of exercise physiologists and coaches changing old ideas and concepts and accepting new ones has been slow. Both should examine the new information available and use it to proceed with the next series of research studies and coaching concepts, respectively.

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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

 


Saturday
Aug132011

Exercise in the Heat - Thermal Physiology, Performance Implications and Dehydration

By: Douglas J. Casa, PhD, ATC, CSCS
From: Journal of Athletic Training 1999;34(3):246-252
Site Link: National Center for Biotechnolgy Information
Articel Link: Exercise in the heat: Fundamentals of Thermal Physiology, Performance Implications and Dehydration


Objective: Exercise in the Heat

Objective: To present the critical issue of exercise in the heat in a format that provides physiologic foundations (Part I) and then applies the established literature to substantial, usable guidelines that athletic trainers can implement on a daily basis when working with athletes who exercise in the heat (Part 11). Data Sources: The databases MEDLINE and SPORT Discus were searched from 1980 to 1999, with the terms "hydration," "heat," "dehydration," "cardiovascular," "thermoregulatory," "physiology," and "exercise," among others. The remaining citations are knowledge base. Data Synthesis: Part I introduces athletic trainers to some of the basic physiologic and performance responses to exercise in the heat. Conclusions/Recommendations: The medical supervision of athletes who exercise in hot environments requires an in-depth understanding of basic physiologic responses and performance considerations. Part I of this article aims to lay the scientific foundation for efficient implementation of the guidelines for monitoring athletic performance in the heat provided in Part II.

Key Words: cardiovascular, heat stress, thermoregulatory

Exercise in the heat, as compared with a neutral environment, causes many physiologic changes in the dynamics of the human body, including alterations in the circulatory, thermoregulatory, and endocrine systems. Many interrelated physiologic processes work together to sustain central blood pressure, cool the body, maintain muscular function, and regulate fluid volume. Attempting to sustain exercise (especially if it is intense) in a hot environment can overload the body's ability to properly respond to the imposed stress, resulting in hyperthermia, dehydration, deteriorated physical and mental performance, and a potentially serious (even fatal) exertional heat illness.

Circulatory Responses

The circulatory responses to exercise involve 3 important components: skin and muscle vasodilation, nonactive tissue vasoconstriction, and maintenance of blood pressure' (Figure 1). Skin vasodilation occurs in proportion to the degree of heat load (both exogenous and endogenous),2'3 and the amount of blood supplied to the muscles is dictated by the intensity of the exercise. Constriction of the splanchnic vascular system (supplying the kidneys, stomach, and other abdominal organs), in addition to an overall increase in the cardiac output, allows increased blood flow to the active tissues.

However, when intense exercise occurs in the heat, the cardiovascular (CV) system simply cannot meet the maximal demands of the skin (to decrease thermal load) and the muscle simultaneously.1 8 Ultimately, maintenance of blood pressure will take precedence over skin blood flow (ie, body cooling) and muscle blood flow (ie, performance capacity), but simultaneously increases the rate of hyperthermia and metabolic inefficiency.1' 10" This prioritizing can result in hyperthermia, especially in populations committed to maximal physical exertion (soldiers, athletes, etc). The metabolic changes are reflected in an increased lactate level, which results from decreased hepatic blood flow; muscle vasoconstriction (which influences waste removal, oxygen delivery, buffering capacity, etc); and an increase in muscle temperature. 1 Variations in the onset of these changes can alter the rate at which the athlete experiences fatigue.

Decreased venous return reduces the stimulation of pressuresensitive baroreceptors in the right heart and the pulmonary circulation.12 Messages are then sent to the medullary CV control centers, which can cause muscle or skin vasoconstriction, or both, thereby preserving blood pressure and CV function. 1,13 Minimal decreases in cardiac output have been found in subjects exercising at submaximal intensities in the heat."'3"14 An increase in heart rate compensates for the decreases in stroke volume, and CV capacity is not hindered, unless extreme sweat rates or lengthy exercise sessions, for example, induce significant dehydration. But when maximal exercise is attempted in the heat, the heart rate's finite limit does not compensate for the larger decreases in stroke volume, due mostly to shunting of blood to the skin and active muscle and to the progressive dehydration. 1"7"13 Rowell' concluded that the end result is decreases in both Vo2 and perfonnance capacity.

Thermoregulatory Responses

The circulatory and thermoregulatory responses are interrelated, with each influencing and being influenced by the other. The degree of stress imposed by exercise in a hot environment is determined by the thermal load. Heat gain must be equaled (or closely matched) by heat dissipation if the athlete wishes to continue exercising at a consistent performance level. Exogenous factors that contribute to heat acquisition include ambient temperature, wind speed, humidity, solar radiation (direct and indirect), ground thermal radiation, and clothing.'5 Ambient temperature and humidity are the major contributors; lack of wind in the presence of high humidity and high ambient temperature can impose severe heat stress because copious sweating is not cooling the body (sweat is not evaporating from the skin), which exacerbates the hyperthermia.16 The predominant endogenous factor is the metabolic heat from contracting muscle (capable of increasing 15 to 20 times during exercise in healthy young adults), which is profoundly influenced by the intensity of the exercise. The body attempts to balance internal temperature by dissipating heat via conduction, convection, evaporation, and radiation. 15,17 Heat dissipation while exercising depends on the ambient temperature. As ambient temperature rises, radiation and convection decrease markedly; heat loss by conduction is insignificant at almost all times.15"8 Convection is compromised by a temperature gradient change between the peripheral blood vessels and the skin. Heat loss from evaporation thus becomes the predominant heat-dissipating mechanism for a subject exercising in a hot environment. In a hot, dry environment, evaporation can account for as much as 98% of cooling, whereas in a hot, wet environment, evaporation is still nearly 80% (the rest is largely convection and radiation).'8 The sweating response is critical to whole-body cooling during exercise in the heat; any disturbance in this mechanism (eg, high humidity, dehydration) can have profound effects on physiologic function and athletic performance. The reader is referred to Stitt'7 and Werner15 for in-depth analyses of the heat balance equations, but, in short, heat acquisition (from exogenous and endogenous sources) must be matched by the combined 4 heat-dissipation pathways to maintain thermal balance: heat storage = heat production minus heat dissipation or plus heat acquisition. This may be expressed as ±S = (M-W) ± C ± K ± R -E, where S is body heat storage, M is metabolic heat production, W is external work, and C, K, R, and E represent convection, conduction, radiation, and evaporation, respectively.17"19 When heat dissipation fails to equal heat acquisition, hyperthermia increases skin blood flow, and, depending on the environmental conditions, heat release via convection, radiation, and evaporation.19 Skin blood flow changes are regulated not just by body temperature, but also by blood pressure, brain blood flow temperature, skin-core temperature gradients, muscle metabolism, etc. As discussed previously, maintenance of blood pressure takes precedence over heat dissipation.

Kenney and Johnson2 and Sawka and Wenger7 reported on the integration of these regulatory processes, in addition to the important role of the efferent mechanisms controlling skin blood flow (ie, passive withdrawal of constrictor tone, reflex vasoconstriction, and active vasodilation). The inherent changes in sweating rate and body cooling associated with skin blood flow changes assist in controlling hyperthermia (the primary controller of sweating rate). Nadell' and Sato20 offer the best explanation of eccrine sweat secretion. Warmer air temperatures are associated with increased sweating.2' Since only evaporation is an efficient mode of heat dissipation in this situation, physiologic strain is exacerbated by the decreased extracellular fluid volume associated with copious sweating. In the short term, the body is being cooled, but increased dehydration alters CV functional capacity, which can lead to decreased skin blood flow and sweating rate as the body attempts to maintain the central circulation and blood pressure. In a cooler environment (with a larger temperature gradient between skin blood flow and skin temperature), the body can avoid hyperthermia while minimizing fluid losses via convection and radiation. In a warm, humid environment, all the critical variables work against the exercising individual: convection and radiation are nearly nonexistent,10 and evaporation is thwarted by a small water vapor pressure gradient.7 With no heat dissipation, dehydration occurs, and the core temperature rises at a potentially dangerous rate.22 The decreased physiologic function associated with hyperthermia is well documented, 23 and the rate of onset of hyperthermia can be influenced by fitness,15 acclimation,24 type of exercise,25 age,26 and numerous other factors.

Performance Implications

The additive effect of the stresses imposed by exercise in the heat will ultimately compromise athletic performance. In addition, exercise in the heat often causes dehydration (since rates of sweating are rarely matched by rates of rehydration), which further exacerbates the situation.2728 It is extremely difficult to separate the effects of heat and dehydration, since they often occur in parallel during prolonged exercise, but some researchers have attempted to match sweat loss with fluid intake during exercise. Rowell et al29 found large reductions in stroke volume despite maintained central blood volume. Enhanced physical fitness and heat acclimatization increase heat tolerance independently but similarly and optimize heat tolerance when combined.30 Sawka et a13' reported a 7% decrease in maximal aerobic power in the heat as compared with euhydrated subjects in cool temperatures. Febbraio et a132 and Galloway and Maughan33 showed the effects of increasing temperature on the capacity to exercise to exhaustion. Febbraio et al32 found that subjects could exercise for 95 minutes at 37°F (2.78°C), 75 minutes at 68°F (20°C), and only 33 minutes at 104°F (400C), indicating an inverse linear relationship between ambient temperature and performance capacity. The 20-minute difference in the 2 cooler environments is an important reminder that extreme heat is not necessary for potential performance decrements. Galloway and Maughan33 concurred, reporting that subjects exercised for 92 minutes at 52°F (11.11°C), 83 minutes at 70°F (21.11°C), and 51 minutes at 86°F (300C). These studies supported the concept of Sawka et al34 that heat stress and dehydration can act independently to compromise physiologic function when the extreme demands for skin blood flow cause decreased cardiac output, which in turn limits the supply of oxygenated blood to the entire body. When heat stress and dehydration occur together (as they often do), this physiologic condition is exacerbated. In addition to performance decrements, the potential for an exertional heat illness increases as the environmental conditions worsen. The American College of Sports Medicine22 provided a concise analysis of how to determine when the environmental conditions preclude physical activity and what procedures should be followed to ensure safe participation in a hot environment (to be addressed in part II).

Dehydration and Exercise

Each physiologic system in the human body is influenced by severe dehydration. The degree of dehydration will dictate how much these systems are compromised. Figure 2 describes similar terms used to describe water losses and gains. The work of Sawka and colleagues34-36 is definitive in the domain of hypohydration and its impact on performance and physiologic function. Their laboratory, located within the US Army Research Institute of Environmental Medicine in Natick, MA, is one of the preeminent locations in the world for investigating the human body's capacity to perform exercise in a variety of environments.

Physiologic Changes

Isolating which particular physiologic changes contribute to decrements in performance is difficult, if not impossible. The interrelation of the human body's systems means that any change in one system influences others. However, recent research has begun to uncover what occurs when an athlete becomes dehydrated during exercise. Dehydration induces changes in the thermoregulatory, cardiovascular, plasma, gastrointestinal, endocrine, muscular, and metabolic responses to exercise.37'38 As discussed earlier, the CV system of a ypohydrated, exercising subject attempts to maintain cardiac filling pressure while sacrificing peripheral circulation,' but hypohydration in combination with heat dissipation at the skin and increased muscle blood flow limits CV capacity, regardless of how much blood is shunted from the periphery to the central circulation. 1 39'40 Increased viscosity and decreased volume of blood returning to the heart decrease filling pressure, and in turn, stroke volume. 14.41,42 To counteract these changes, heart rate rises to its limit, but then cardiac output begins to fall, signaling CV system responses, which limit skin and muscle function.

3443 The end result is a diminished ability to dissipate heat, and thus, heat production exceeds heat loss. Excess heat in combination with decreased muscle perfusion limits performance and causes thermal strain.1 35 Exercising while dehydrated has some effects on the thermoregulatory system444-49 (Table) and may negate the physiologic advantages resulting from increased fitness24'50 and heat acclimatization. 24'51 Sawka et al36 noted decreased heat tolerance (by more than halt) in subjects dehydrated by 8% of body weight and found that soldiers became exhausted at lower core temperatures when hypohydrated. While 8% is an extreme amount of dehydration rarely encountered in sports, the study emphasizes the decreased heat tolerance associated with dehydration. The human body is composed of about 65% water, separated into extracellular (plasma and interstitial) and intracellular fluid.52 At rest with normal hydration, about 45% of body weight is intracellular fluid, 15% is interstitial fluid, and 5% is plasma.52 Exercise, heat stress, and dehydration all influence the redistribution of body fluids with changes in hydrostatic and osmotic pressure.52'53 For instance, because sweat is hypotonic to plasma, the dehydrated athlete experiences plasma hyperosmolality, which affects the distribution of fluids.35 Mild dehydration causes mostly extracellular space fluid losses, but, as dehydration worsens, proportionally more fluid is lost from the intracellular space.54'55 Nose et a156 reported that the loss of intracellular and extracellular fluid is largely from muscle and skin. This selective regulation of body fluids preserves the internal environment of the most essential organs: for instance, the brain and liver.35 Changes in the distribution of body fluids are associated with the ability to mobilize fluids from the intracellular space, which is intimately linked with sweat sodium concentrations.57 Thus, the de- creased sweat sodium concentrations noted after heat acclimatization may help to conserve plasma volume during dehydration. Ultimately, the fluid redistribution that results from dehydration causes a hypovolemic hyperosmolality,58 which stimulates the volume and fluid receptors in the body to conserve fluid and stimulate rehydration.

Plasma changes have been cited as the major cause for the thermoregulatory changes during hypohydration. Hyperosmolality59- 61 and hypovolemia'6 62 are likely responsible for the changes noted in skin blood flow and sweating rate and the resultant rises in core temperature.93540 Fortney et al"6 have argued that hypovolemia is primarily responsible for the thermoregulatory changes by reducing central blood volume, which may alter the feedback to the hypothalamus via the atrial baroreceptors. The hypothalamic thermoregulatory centers may then decrease the blood volume perfusing the skin in an attempt to reestablish a normal central blood volume. Some studies have provided support for this hypothesis,6364 but it is clearly not the only variable influencing thermoregulation during hypohydration. Two primary hypotheses have been proposed to explain the role of hyperosmolality on the thermoregulatory system. The first is a strong osmotic pressure influence of the interstitium, which may limit the available fluid sources for the eccrine sweat glands.65 While this pressure is likely to exert some influence, it seems more feasible that brain regulation, the second hypothesis, has the largest contribution. The neurons surrounding the thermoregulatory control centers in the hypothalamus are quite sensitive to osmolality.6'67 Thus, changes in the plasma perfusing the hypothalamus can affect body water regulation and the desire for fluid consumption.4043 The human body is well equipped to identify small changes in the internal environment and to respond with appropriate modifications. While research may someday identify a proportional contribution to the age-old question of hyperosmolality versus hypovolemia, it is most likely that both will always be considered major contributors to the mechanisms that perturbate body fluid regulation. Potential muscle changes associated with dehydration include an increased rate of glycogen synthesis,"'48 compromised buffering capacity of the muscle tissue,38 elevated muscle temperature,68 and decreased substrate exchange.",38

These factors are caused by a decrease in blood flow perfusing the muscle tissue, which may alter the dynamics during the recovery between contractions.69 These muscle changes seem to occur when exercise exceeds 30 seconds, which is reasonable from a metabolic perspective.70 These arguments would support the notion that strength during short-term activity is not affected until dehydration becomes more pronounced, largely due to the fact that the muscle energetics of very short-term activity are, for the most part, self-contained, and thus, not as influenced by changes in blood flow.38

Performance Implications

Research investigating the role of dehydration on muscle strength has yielded conflicting results. Some studies have shown performance decrements,7174 while others have shown no changes.'4'75 However, when strength decrements were found, they usually occurred when dehydration exceeded a 5% reduction in body weight.34'49 In addition, dehydration resulting from fluid restriction seems to be more harmful than that caused by exercise and heat stress; thus, the fluid restriction may be partially inducing a caloric deficit.34 The research on muscle endurance is a bit more conclusive. A sampling of the numerous studies14'7276-79 that have addressed the influence of dehydration on muscle endurance reveals, generally speaking, that 3% to 4% dehydration elicits a performance decrement but some studies investigating greater levels of dehydration did not find any differences in performance.34 Horswill38 concluded that, in wrestlers (who are frequently hypohydrated), combined hypohydration and maximal or near-maximal muscle activity exceeding 30 seconds may combine to decrease performance. Environmental conditions may also play an important role in muscle endurance, 34'68 and, since greater hypohydration often occurs in hot conditions, more studies should investigate this relationship. The research concerning maximal aerobic power and the physical work capacity for extended exercise is also relatively conclusive and consistent. Maximal aerobic power usually decreases when dehydration exceeds a 2% to 3% reduction in body weight, and, when performed in the heat, the decrements are exaggerated.34 Nearly every study that has examined physical work capacity has shown some degree of performance decrement.34 Even with only 1% to 2% hypohydration in a cool environment,8081 a decrement is noted. Pinchan et a182 and Walsh et a183 noted decreases in physical work capacity with less than 2% dehydration during intense exercise in the heat. As expected, when dehydration increased, physical work capacity decreased, sometimes by as much as 35% to 48%,84 and physical work capacity often decreased even when maximal aerobic power did not change.80'8"85 Buskirk and Puhl69 suggested that some of these decrements with low to moderate levels of hypohydration may be partly due to an increased perception of fatigue. The degree of change in physiologic function will be dependent on various exercise parameters, including intensity, duration, environmental stress, and individual factors.

Conclusion

Exercise in the heat triggers a disturbance of the internal environment of the human body. Understanding the responses requires an astute ability to focus on many independent physiologic processes that function cooperatively. The athlete wishes for these systems to rise to any challenge, but often excessive heat, dehydration, or both cause some degree of decrement in performance. The ensuing part of this 2-part series about exercise in the heat attempts to identify ways in which athletic trainers and athletes can work toward minimizing the decrement by maximizing heat dissipation and body fluid balance.

Acknowledgement

I would like to dedicate this paper to the memory of my former supervisor, Dean Leo W. Anglin, Jr, PhD. I would later learn that he took his final breaths as I wrote this article. He was a visionary in the field of education, and the passion that drove him was contagious. I shall strive in his memory.

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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.

Saturday
Jul232011

A Lightweight Rower's Diet

By: Patrick Dale.
From: Live Strong: Lance Armstrong Foundation.

Overview: A lightweight Rower's Diet

Rowing is a relatively old sport whose governing body, the International Rowing Federation, was formed in 1892. Rowers compete individually or in crews of two, four or eight and are categorized by weight: Lightweight men must weigh less than 72.5 kg or 160 lbs. while lightweight women must weigh less than 59 kg or 130 lbs. Rowers weighing more than these figures are classed as heavyweights. Lightweight rowers must be careful not to gain too much weight otherwise they will find themselves ineligible for lightweight competition. For this reason, diet is especially important for lightweight rowers.

About Rowing

Rowing is a demanding whole-body sport that requires strength, power and fitness. The legs, back and arms are especially important in rowing. Rowing with one oar is called sweep rowing while using two oars is called sculling. Both types of rowing require very high levels of fitness. Training for rowing is vigorous and includes not just rowing but also weight training, circuit training and running or cycling. According to "The Sports Book" by Ray Stubbs, rowers consume an average of 6,000 calories per day to fuel their training, but this very much depends on the size of the rower and amount of training being performed. 

About Rowing

Rowing is a demanding whole-body sport that requires strength, power and fitness. The legs, back and arms are especially important in rowing. Rowing with one oar is called sweep rowing while using two oars is called sculling. Both types of rowing require very high levels of fitness. Training for rowing is vigorous and includes not just rowing but also weight training, circuit training and running or cycling. According to "The Sports Book" by Ray Stubbs, rowers consume an average of 6,000 calories per day to fuel their training, but this very much depends on the size of the rower and amount of training being performed.

Fueling Workouts

The primary fuel in rowing workouts is carbohydrate. Carbohydrate from foods such as bread, rice, pasta, fruit and vegetables is broken down and converted to glucose to provide energy for muscular contractions. Hard-training rowers should ensure they consume enough carbohydrates to fuel their rigorous workouts. Sports nutritionist and author Anita Bean recommends that hard-training rowers should consume 8 to 10 g of carbohydrate per kilogram of body weight. Carbohydrates also provide plenty of vitamins, minerals and fiber, so rowers should try to eat wholesome sources of carbohydrates while limiting the consumption of refined foods and sugars. 

Muscle Repair

Rowing and rowing training cause muscle damage at a cellular level. With adequate rest and good nutrition, muscles repair themselves and get stronger. The primary nutrient required for post exercise muscle repair is protein. Rowers should consume around 1.2 to 1.6 g of protein per kilogram of body weight to ensure they have adequate protein to repair their muscles after intense exercise. Good protein foods include beef, pork, chicken, turkey, fish and eggs. Protein consumption should be spread evenly throughout the day to ensure muscles receive a regular supply of protein-derived amino acids.

Fats

Although fats are very calorie dense, they are also important for health. Fats are essential for the transportation and utilization of vitamins and minerals, are anti-inflammatory and a useful source of energy. Because fat provides a lot of calories, lightweight rowers should be careful not to consume too much fat in order to avoid gaining weight. Most experts agree that around 30 percent of calories should be derived from fat and split evenly among saturated, monounsaturated and polyunsaturated fat.

Weight Management

Unlike heavyweight rowers who have no upper weight limit, lightweight rowers much avoid getting too heavy - especially as the competitive season approaches. To maintain your body weight, your calorie intake must equal your calorie expenditure. If you are over your correct rowing weight, you should endeavor to start your weight-loss diet in plenty of time before the season to avoid having to crash diet which may affect your rowing training due to reduced energy levels. By setting the goal of 1 lb. per week, you can estimate how long it will take you to get to your correct competitive weight. To lose 1 lb. a week, you need to reduce your calorie intake by around 500 calories a day.

References

"The Sports Book"; Ray Stubbs; 2009

"The Complete Guide to Sports Nutrition"; Anita Bean; 2009 

"Nancy Clark's Sports Nutrition Guidebook"; Nancy Clark; 2008

Saturday
Jul232011

Fuelling Rowers

By: Jennifer Doane.
From: American Dietetic Association. Copyright ©2006: This handout may be duplicated.
PDF Link: Fuelling Rowers

Fuelling Your Sport

• The number of calories needed by rowers depends on the intensity of training. Recreational rowers need fewer calories than competitive rowers.

• When training is very intense and lasts a long time, rowers can need 20.5 to 21.5 calories per pound of body weight per day (45 to 47 calories/kg/day). Male heavyweight rowers may need more than 6,000 calories per day, and female heavyweight rowers need at least 3,000 calories each day.

• When rowers improve their stroke, they don’t use as much energy. Therefore, they may need to eat fewer calories than they did when they were beginners.

• Carbohydrate is the most important fuel for rowers, but some rowers don’t get enough. You need 2.3 to 3.2 grams of carbohydrate per pound of body weight per day (5 to 7 g/kg/day) during training and competition. During training, you should aim for the higher end of the range (3.2 grams/pound/day). Good sources of carbohydrate include whole grain breads and cereals, fruits, and vegetables.

• Rowers need 0.55 to 0.8 grams of protein per pound of body weight per day (1.2 to 1.7 g/kg/day). You need the most protein during the early phases of training. Good sources of protein include fish, chicken, turkey, beef, low-fat milk, cheese, yogurt, eggs, nuts, and soy.

• Eat about 0.45 grams of fat per pound of body weight per day (1 g/kg/day). Choose heart-healthy fats, such as canola oil, olive oil, and nuts.

Fluid Needs

• When you compete in a weight class, you may think about using dehydration practices to make weight at the last minute. However, practices such as working out in a rubber suit in a sauna, limiting fluids, vomiting, and taking diuretics are very dangerous. They can lead to serious health problems or diminish your performance.

• Try to make weight well before the start of the competitive season. To get to a competitive weight, focus on eating less, not fluid restriction.

• Two hours before every workout and competition, drink 2 cups of fluids.

• Drink about 3 cups of fluid for each pound lost during training or competition.

• One way to know if you are drinking enough is to monitor your urine colour. Urine will have a pale, straw colour when you are hydrated.

• Use sport drinks to get fluids, carbohydrates, and electrolytes that your body loses when you’re active.

Supplements Commonly Used by Rowers

• Creatine may increase performance in 1,000-meter rowing events.

• Creatine supplementation may also help you recover more quickly from weight training sessions, which could help you train harder.

• Creatine monohydrate powder is a common type of creatine supplement. The recommended dose is 3 to 5 grams per day. Taking larger amounts does not give you added benefits.

Creatine is not recommended for athletes younger than 18 years because it is not known whether creatine is safe for this age group.

• Energy bars are a convenient way to get more calories and nutrients. Choose an energy bar that contains more carbohydrate than protein or fat. Many energy bars do not taste very good, so find a bar you like to eat. Bars are more expensive than other food, and they don’t contain any magical ingredients to improve performance.

 

Top Three Nutrition Tips to Improve Performance

1. Manage your weight in the off-season instead of cutting weight in-season. A sports dietician can create an eating plan that allows you to make your desired weight well before the season starts. Some athletes have unrealistic goals for body composition. A sports dietician can help you determine whether your goals are realistic.

2. Develop a hydration plan along with your training plan. Dehydration hurts performance and increases the risk for heat illness. Choose sport drinks when rowing on hot, humid days. Drink 2 cups of fluid 2 hours before exercise and drink plenty of fluids after your workout.

3. If you want to gain weight, plan ahead.

Heavyweight rowers often want to gain weight in a short time period, but healthy weight gain, like weight loss, will not happen in a day or two. If you want to gain weight, increase your calories by 500 to 700 per day. If you use high-calorie and high-protein liquid meals, use them between meals or before bed for best results.

 

Nutrition Prescription:

______ calories per day

______ grams of carbohydrate per day

______ grams of protein per day

______ grams of fat per day

______ cups of fluid per day

Special concerns: