The Optimum Composition for Endurance Sports Drinks

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

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

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

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

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

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

The issues with sports-drink composition are as follows: 

Exercise Depletes Water and Salt

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

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

Exercise Depletes Carbohydrate

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

Drinks Can Offset These Depletions

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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


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


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



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


Endurance Performers and Iron-Deficiency

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

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

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

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

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

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


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

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

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

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

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


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


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


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

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

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


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

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

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

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


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

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


Sensitivity of reticulocyte indices to iron therapy in an intensely training athlete. In: Br J Sports Med ( ENG-LAND) Sep. 199832 (3) p259-6o ISSN: 0306- 3674

Serum ferritin and anaemia in trained female ath- letes. In: Int J Sport Nutr (UNITED STATES) Sep 1998 8 (3) p223-9ISSN: 1050-1606

Prevalencia de ferropenia en la poblacion laboral femenina en edad fertil. In: Rev Clin Esp (SPAIN) Jul1996 196 (7) p446-50 ISSN: 0014-2565

Practical issues in nutrition for athletes. In: J Sports Sci (ENGLAND) Summer 1995 13 Spec No pS83-90 ISSN: 0264-0414

Micronutrients and exercise: anti-oxidants and minerals. In: J Sports Sci (ENGLAND) Summer 199513 Spec No pS11-24 ISSN: 0264-0414

Iron stores in professional athletes throughout the sports season. In: Physiol Behav (UNITED STATES) Oct 1997 62 (4) p 811-4 ISSN:0031-9384

The clinical value of serum ferritin tests in endurance athletes. In: Clin J Sport Med (UNITED STATES) Jan 1997 7 (1) p46-53 ISSN: 1050-642X

Monitoring intensive endurance training at moderate energetic demands using resting laboratory markers failed to recognise an early overtraining stage. J Sports Med Phys Fitness ( ITALY) Sep. 1998 38 (3) p 188-93ISSN:0022-4707

Increased blood viscosity in iron-depleted elite athletes. In: Clin Hemorheol Microcirc (NETHERLANDS) Jul1998 18 (4) p 309 -18 ISSN: 1386-0291

Iron supplementation in athletes. Current recommendations. Sports Med (NEW ZEALAND) Oct 199826 ( 4) p207-16 ISSN: 0112-1642

Iron nutritional status in female karatekas, hand- ball and basketball players, and runners. In: Physiol Behav (UNITED STATES) Mar 199659 (3) p449-53 ISSN:0031-9384

{Sport-anaemia: studies on haematological status in high school boy athletes}. In: RINSHO BYORI (JAPAN) JUL 199644 (7) p616-21ISSN: 0047-1860


Strength Training for Women: Hormonal Considerations

By: C. Harmon Brown, M.D.
Chair of USATF's Sports Medicine and Sciences Committee.
From: Published in Track Coach: No137
Site Link: Coachr.


Dr. Brown, Chair of USATF's Sports Medicine and Sciences Committee, referred to this in a note to us as a "think piece." He calls for coaches and scientists to continue this kind of study. This is a well-documented article, which may lead the interested coach to investigate further. We welcome response to this important article.

Strength training to enhance sports performance and improve fitness is now a common means of exercise for women. It has progressed to the point that there is now a world championships in weightlifting for women.

For many years resistive exercises for women were shunned for fear of these athletes becoming "masculinized" through the use of heavy weights. However, early studies showed that women were able to exhibit considerable improvements in strength with only minimal degrees of muscle hypertrophy (2). These researchers pointed out that the likelihood of major muscle hypertrophy from resistance training was small in comparison to males, as women have blood levels of the anabolic hormone testosterone which are only 5-10 per cent of those of men.

Many subsequent studies have borne out these early findings. Further, resistance training itself does not appear to increase basal levels of testosterone in women, and strength gains are not correlated with blood testosterone levels (3-5).

The endocrine aspects of exercise science have increased greatly in recent years, especially in the areas associated with resistance training. Assessing the roles of the various hormones as to the cause-and- effect relationships in response to any exercise stimulus can be very complex.
Hormonal levels in blood and tissues are influenced by their production from the parent organ, clearance from the blood by the liver, kidneys, and other peripheral tissues, and their binding to specific receptor sites in target organs.

In addition, steroidal hormones such as androgens, adrenal hormones, and ovarian hormones circulate in the blood bound to specific carrier proteins, with only a tiny fraction in the "free" form which is available to tissues.

Evaluation of the numerous studies which have been carried out concerning the responses of the endocrine system are further complicated by the variety of test protocols which have been utilized. Aerobic vs. resistance loading produces different hormonal responses, and even seemingly similar studies may yield different results. The athlete's state of training and nutrition can also influence the metabolic and hormonal outcomes.

There are at least three anabolic hormones which are responsible for muscle hypertrophy: testosterone (and dihydrotestosterone), pituitary growth hormone (GH), and insulin-like growth factor I (IGF-I), formerly called somatomedin-C.


Initially, studies focused on the role of testosterone in response to an exercise stimulus, especially resistive loading. It soon became apparent that, in addition to different basal levels between men and women, the response to exercise is quite different. Following a bout of resistive exercise, the male's testosterone level rises considerably, while in women the values change little, if at all.
Further, the disposition of testosterone in the body differs between the sexes. In males, about 50 per cent of the testosterone is bound to receptors in muscle, while only about 10 percent is cleared in this manner in women. However, women do show a greater response of the weaker adrenal androgen, androstenedione.

Concerns that resistive training in women raises basal testosterone levels, or that higher basal testosterone levels are accompanied by greater strength gains, have not been borne out.


Growth hormone responds to both aerobic and resistive exercise. Growth hormone stimulates muscle growth by facilitating the transport of amino acids across cell membranes, activating DNA transcription in the muscle cell nucleus, thus increasing the amounts of RNA and protein synthesis.


Insulin-like growth factor I (IGF- I) is a potent anabolic factor. It is believed that growth hormone's effects are mediated through IGF-I. IGF-I is stored in the liver and peripheral tissues. It is released slowly (16-28 hours) after growth hormone stimulation. In those situations in which it was measured, IGF-I levels have risen little or not at all after exercise bouts which have been sufficient to elevate growth hormone concentrations. Further, increases in IGF-I did not seem to correlate with the rises in GH. The reasons for this are not clear.

It would appear from the foregoing that the growth hormone IGF-I complex plays a significant role in the development of muscle hypertrophy and strength in women. Hence, strength programs for women should focus on maximizing growth hormone production.


In a series of elegant studies, W. Kraemer, et al. (9-12) examined the hormonal responses to a wide variety of resistive training protocols in both men and women. By varying the resistive load (5-RM vs. l0-RM) and the rest interval (1 minute vs. 3 minutes), they were able to demonstrate considerable differences in the response of several hormones.

In summary, the greatest rises in GH occurred with the protocol in which eight different exercises were used, with three sets of each exercise. The resistance was l0-RM, or approximately 70-75 percent of the l-RM, and the rest interval was one minute between each exercise and between each set.


Similar responses were seen in both men and women, with the women having somewhat higher baseline GH levels, and slightly greater exercise responses. However, in all prior studies by these and other authors, women were studied only during the follicular phase (first half) of the menstrual cycle.
Only recently has the effect of the menstrual cycle on various hormonal responses to resistive training been assessed (6). RR Kraemer, et al. (7, 8) studied the changes in hormonal response which occurred during both the follicular and luteal phases of the cycle in the same group of subjects. These women were subjected to a moderate exercise regimen of three sets of 10 repetitions of four different exercises with a 2- minute rest interval. There was a significantly higher GH response during the luteal phase, as well as much higher estradiol levels. Other studies have suggested that the female hormone estradiol facilitates the release of growth hormone.


These studies suggest that strength training programs for women should be tailored to each athlete's menstrual cycle. Although there have been no studies to validate the effect of these cyclic hormonal variations on muscle growth and strength development, the research findings are strongly suggestive that such a study would be of considerable value.

Until such a study is done, however, imaginative strength coaches should consider devising strength development programs which take into account these hormonal fluctuations which occur during the menstrual cycle. Such considerations might be especially valuable during the basic "hypertrophy" mesocycle of a strength development program.

These programs should consider:

  1. During the luteal phase (second half) of the menstrual cycle strength training should consist of "moderate intensity" loading, using 3-4 sets of 8-10 repetitions at 65- 75% of the 1- RM, done three times a week. These exercises should involve the large muscle groups of the upper and lower extremities and trunk, i.e., bench press, squats, power cleans, leg press, sit-ups, dead lifts, etc.
  2. The rest interval between sets and exercises should be no more than two minutes, and preferably shorter.
  3. A similar routine also may be of value during the follicular phase (first half) of the cycle, although the estradiol and GH responses may be lower.
  4. f the athlete is using oral contraceptives, no phasic change in GH response can be expected (1) unless the oral contraceptive is of the "tri-phasic" variety. Several studies of athletes using oral contraceptives have been done. These have yielded conflicting results as to whether there is a greater-than-expected GH response, probably because of variations in hormonal strength and type, and in exercise protocol.
  5. During the "strength" phase of the training cycle (lower repetitions, higher loading), i.e., four sets of five repetitions at 80% of l-RM, a lesser response of estradiol and GH is to be expected, and the training program need not be adapted to the menstrual cycle.

It is hoped that this paper will stir some thought and even controversy in the strength-training community and will lead to further studies and some empirical trials by innovative coaches and scientists.


The Function of the Mid-Torso In Sports Activities

By: Adrian Faccioni.
Lecturer in Sports Coaching, University of Cabberra, Australia.
From: Published in Track Coach: No133 - Fall 1995.
Site Link: Coachr.

1. Anatomy & Kinesiology.



Most sports encompass relatively large movements of the trunk. Since the trunk segment has a large mass, great demands are exerted on the trunk musculature, particularly if the trunk movements are to be performed with high accelerations. Also the trunk has a critical role in the maintenance of stability and balance when performing movements with the extremities.

Sporting activities requiring running or jumping place pressure on the lumbo-pelvic region (that includes the 4th and 5th lumbar vertebra), the pelvis and the hips as this region becomes the hub of weight bearing. The superior forces (from torso, head and arms) meet the inferior forces transmitted from the ground through the lower extremity.

No part of the body is more vulnerable to tissue strains and sprains. This point is the center of all body movements and efficient body movements (as required in sprinting) can be critical in maintaining the stability of an anatomically correct body position, that of the Abdominal muscle groups, erector spinae (making up the mid-torso region) and the gluteus maximus (Porterfield 1985).

A study by Comerford, et al. (1991) analyzed the mid-torso muscle groups to see which group had the greatest impact on lumbo-pelvic stabilization. Results indicated that oblique muscle groups were the most important for this stabilization (especially from pelvic rotation forces) as found in high-speed sprint movements.

To assist in sprint acceleration, powerful arm drive will allow for a more rapid and powerful leg extension. The limitation with this technique is that large rotational forces can be placed upon the mid-torso musculature. If there is inadequate stability in this region, rotation of the pelvis will occur to counteract shoulder rotation resulting in poor technique and inefficient force application; therefore a slower athlete will be the result.

At an elite level, upper body strength is emphasized in sprint athletes out with a concurrent development of mid-torso strength to allow efficient usage of this additional strength during high-speed sprinting movements.

The naturally occurring wide pelvis of the mature female also leads to the above problem and mid-torso strength is absolutely vital if the coach wishes to maximize efficient technique at maximal speed in his/her female sprint athletes. Hip rotation is required to maximize stride length, but if excessive, then poor technique will result and if combined with a poor pelvic tilt, then major inefficiencies will result, leading to either poor performance, injuries or both.

Apart from resistance to rotational forces, there must be support of the pelvis to minimize excessive anterior pelvic tilt. An excessive anterior tilt indicates poorly toned mid-torso musculature and this can increase the lordotic curve (lower back arch) in the lumbar region. This can increase the strain on the facet joints in the vertebral column and can result in the iliopsoas going into spasm to protect the lower core from injury.

Also increased pressure on the neural plexus from the lumbar region can result in nerve irritation (e.g. sciatic nerve) which can then affect the optimal functioning of lower limb musculature that can have deleterious effects if maximal effort work (e.g., 100% sprinting) is performed (such as hamstring strains).

Excessive anterior tilt of the pelvis can limit hip range of motion leading to excessive hip extension and limited hip flexion. This technical position limits stride length and increases ground contact time (which is undesirable for increases in speed performance) due to the athlete's center of gravity being lower than required for maximal sprinting speed.

The demands of sprinting require the abdominals to function in a way that leads to optimal torsional stabilization during explosive contractile sequences, matching the needs of performing up to 5 strides per second (such as that which occurs in an elite sprint race). During sprinting at this rate, the lower limb velocity can reach 80km/h; therefore the stresses placed upon the pelvic stabilizers are extreme and can only be accommodated for with extremely well-developed abdominal (including oblique) musculature (Francis 1992).


The development of a strong mid-torso should be the goal of all speed/power athletes and the preferred procedures for maximizing strength in this region is by the common sit-up. Kinesiologically, the sit-up and its many variations are the ideal exercises to develop the vertebral flexor and rotational muscles (namely the RA, EO & IO).

The mid-torso musculature consists of postural muscles with a high percentage of slow-twitch muscle fibers. Their function is to be able to hold contractions for long periods to maximize trunk stability (Nordel and Frankel 1989, p. 104).

To best condition this region, variations on the sit-up can be used. To maximize abdominal development and minimize stress placed upon the lower back, exercises should be performed slowly (1-4 seconds per repetition) while working on all muscle groups in the mid-torso region.

These exercises should also be performed through a range of motion that minimizes lower back strain, and maximal control is required. When compared to the stress placed upon the lumbar region when standing (assume this is measured as 100%), the full sit-up (Figure 5), even with knees bent and feet flat on the floor, creates a stress equal to 200%.

This load can be decreased if the sit-up is only partial (first 30' from floor) and lessened even more if a reverse sit-up is performed (pelvis lifted off the floor) (Figure 6).

The reverse curl has been shown to increase the activation on the EO and IO as well as the RA (Nordin & Frankel 1989, p. 202). A modification to maximize load and minimize stress upon the lumbar region is to perform a partial crunch as well as a reverse sit-up concurrently (Figure 7) and hold each maximal contraction for four seconds. This minimizes the use of assistant muscle groups and quickly fatigues the musculature targeted in only 5-15 repetitions.

Sit-ups performed fast and or with the feet supported have:

  1. The relative contribution of the hip flexors increasing while the relative contribution of the abdominal muscles decreasing (Sevier 1969).
  2. Increased stress placed upon the lumbar region of the spine.
  3. Decreased load on the abdominal musculature due to increased momentum from the upper body.

The major limitation of the sit-up is the functional application of mid-torso strength transferable from a sit-up routine to the pelvic stabilization required under the stresses of a sprint or any high-speed movement performance. Personal observation of a variety of athletes has highlighted that even the development of very strong mid-torso regions from situps and squat type activities do not automatically transfer to the pelvic and mid-torso positions required to maximize sprinting performance.

Many athletes are strong enough through their mid-torso region but have not developed correct motor patterns to be able to stabilize the body while having rapid upper and lower limb movements (e.g., arm and leg movements in sprinting). To develop the specific strength qualities or transfer mid-torso strength to the required strength positions can be achieved both in a weight room and the field/court/ track situation.


The best adaptation in the mid-torso musculature results from slow isotonic training in combination with isometric training in a range of nonspecific and sprinting-specific body positions.

Once the athlete can perform acceptable slow isotonic (with movement) mid-torso exercises, more sprint specific positioning can be introduced that requires the athlete to place his hips in the necessary posterior tilt position while placing stress upon the mid-torso musculature. Examples of these exercises are:

  1. Abdominal hollowing (Figure 8)
  2. Isometric prone (Figure 9)
  3. Single leg raise with lumbar support (Figure 10).

Abdominal hollowing

To perform abdominal hollowing the athlete can be either in a supine position or standing. The technique is to contract the abdominals "INWARDS" as hard as possible while maintaining normal rib cage positioning. This can be assisted by placing a finger into the belly button and try to push the abdominal wall inwards while maximally contracting. The athlete should continue to breath as normally as possible throughout the exercise; each contraction can be held for up to 60 seconds.

Isometric prone

To perform an Isometric prone exercise the athlete begins on elbows and knees and then takes the knees off the ground while trying to maximally contract the abdominal musculature upwards. If any stress is felt on the lower back, this is an indication that the abdominal wall is not being totally contracted. This position should be held 15-60 seconds depending upon the condition of the athlete.

Single leg raise with lumbar support

To perform a single leg raise with lumbar support, the athlete places the tips of his fingers under the lower back and maximally contracts the back against the fingers. Then one leg at a time is slowly lowered (up to 10 seconds per leg) while maintaining a constant pressure on the fingers. As soon as the pressure decreases, this indicates that the abdominal musculature is beginning to fail and the hip flexors have been activated. At this point if the pressure cannot be regained, the athlete either finishes that repetition or brings the leg slowly back to the starting position until lower back pressure can be regained and then continues the repetition.

These are still "PASSIVE" isometric exercises (done slowly) that once a high competency is reached can be followed by "ACTIVE" isometric exercises that are highly sprint specific.

Examples of these exercises are:

  • Rapid hip extension/hip flexion (Figure 11)
  • Modified Russian Twist with/ without arm swing. The 'MRT' is accomplished while reclining with the buttocks on a raised, fixed seat and with the toes/feet hooked under a rigid padded bar. In this position, the back, shoulders and head are not supported. Then twist at the waist while swinging an arm in the direction of the rotation. (Figure 12)



The weight room training is purely a precursor to what must be achieved at the "on field" situation. This is where true application of the strength gain can be both assessed and true transfer can be completed.

This goal can be achieved in two parts.

  • The correct body positioning can be further applied by several "running drills" that are aimed at correct running form (which usually means correct body posture through the mid-torso).

The "A", modified single leg "A", "B", heel flick and high knee drills (Figure 13) are all aimed at increasing the tilting and rotational stresses that are placed upon the mid-torso musculature. These drills can be done slowly at first and progressively sped up as the athlete's ability to hold the correct position improves.

 The modified single leg "A" places high levels of stress upon the mid-torso region to hold the pelvis in place while the athletes perform very explosive hip flexion and extension movements in a single leg form.

  • The most specific transfer to sprinting is to have the athlete sprint while concentrating on the positioning drilled previously. Sprints should be less than maximal at first, progressing only as the athlete is able to maintain the correct running position. As soon as pelvic stability decreases, the drill should be stopped.

External resistance to increase learning can be in the form of a towing device that the athletes place around their mid-torso and the pressure on this region through each repetition reinforces the control required and increases the level of control as the athlete is having to work harder to maintain good body position under this increased resistance. (Figure 14)

It is important that the resistive load be small enough so that the athlete is able to maintain proper sprint acceleration posture. Bending forward at the waist should be avoided.

In summary, the mid-torso is the link between the upper and lower body and must allow the transfer of strength movements and allow powerful movements of both the upper and lower body to complement each other. The best way to achieve this is to develop mid-torso strength through traditional ways (situps) but ensure functional strength (by more specific mid-torso training methods) is being attained throughout the athlete's training year.



Core Stability: The Inner Unit

By: Paul Chek.
From: A new frontier in abdominal training: IAAF/NSA 4.99.
Site Link: Coachr.
Article Link: The Inner Unit.

ALSO SEE: Core Stability: The Outer Unit.

A new frontier in abdominal training


Paul Chek is an expert in the fields of corrective exercise and high performance conditioning and is the founder of the C.H.E.K Institute in San Diego, California. For over fifteen years he has traveled around the world lecturing, consulting and giving seminars. Paul Chek has been a consultant to the Los Angeles Chiropractic College, the Chicago Bulls, the Denver Nuggets, the US Army Boxing team, Australia's Canberra Raiders and the US Air Force Academy. 


The author states that abdominal exercises can be performed in various ways and asks if the exercises commonly practiced really improve the functionality of the abdominal muscles. From his own studies with patients and clients who performed a high volume of abdominal routines, he concludes that the usual theories of explanation and treatment for back pain are wrong. He recommends the concept of "The Inner Unit", which is a term describing the functional synergy between specific abdominal muscle groups. He describes ideas for Inner Unit conditioning and concludes that Inner Unit training provides the essential joint stiffness and stability needed to give the large prime movers of the body a working foundation.

How many ways can you do an abdominal exercise? Well, if you have been reading the muscle tabloids for the past 20 years you could probably come up with well over 100. Today we have classes devoted to nothing but TRASHING people's abdominal muscles, complete with every variation of crunch, jack knife, side bend and leg raise exercise known to man. Are these classes, or these exercises, really improving the way you look or function, or reducing your chances of back pain?

To find the answers to these questions, in 1992 I began investigating the correlation between abdominal exercises performed, exercise volume and the postural alignment, pain complaints and overall appearance of my clients. To ensure objective observations of postural alignment and responses to specific exercises, I designed and patented calibrated instruments to measure structural misalignment.
In the first year of recording such information as forward head posture, rib cage posture, pelvic tilt and overall postural alignment, it became evident that those performing high volume sit-up/crunch exercise programmes were not showing promising results (see Figure 1)! Those attending "Ab Blast" classes and/or performing high repetition/high volume abdominal routines were not only having a harder time recovering from back pain, they were also showing little or no improvement in their postural alignment.

While studying patients and clients who performed high volume abdominal routines, it became very evident that there was a common link. About 98% of those with back pain had weak lower abdominal and transversus abdominis muscles, while those with no history of back pain were frequently able to activate the transversus abdominis and scored better on lower abdominal strength and coordination tests. To alleviate back pain, I frequently had to suggest that clients stay completely away from any form of sit-up or crunch type exercises. When this advice was adhered to, and exercises for the lower abdominal and transversus abdominis were practiced regularly, back pain either decreased or was completely alleviated and posture routinely improved.

One can always find some "experts" in the health and fitness industries who state that "there is no such thing as lower abdominal muscles," while others suggest that the best treatment for back pain is to exercise on machines that isolate the lower back muscles. My clinical observations lead me to believe both theories are wrong.

In 1987, "Clinical Anatomy of the Lumbar Spine" by Nikolai Bogduk and Lance Twomey was published. This book is important because it was Bogduk who made the first clinical observations of how the abdominal and back muscles worked together as a functional unit. This occurs via the connection of the transversus abdominis and internal oblique muscles to the envelope of connective tissue (thoraco-Iumbar fascia) surrounding the back muscles (Figure 2).

A few years ago, Australian researchers Richardson, Jull, Hodges and Hides began making significant headway in understanding how the deep abdominal wall worked in concert with other muscles, creating what they would later call THE INNER UNIT.

The Inner Unit

The Inner Unit became accepted as a term describing the functional synergy between the transversus abdominis and posterior fibers of the obliquus intern us abdominis, pelvic floor muscles, multifidus and lumbar portions of the longisssimus and iliocostalis, as well as the diaphragm (Figure 3). Research showed that the inner unit was under separate neurological control from the other muscles of the core. This explained why exercises targeting muscles such as the rectus abdominis, obliquus extern us abdominis and psoas, (the same muscles exercised in traditional abdominal conditioning programmes common all over the world) were very ineffective at stabilising the spine and reducing chronic back pain.

Exercising the big muscles (prime movers) was not providing the correct strengthening for such essential small muscles as the multifidus, transversus abdominis and pelvic floor muscles. When working properly, these muscles provide the necessary increases in joint stiffness and stability to the spine, pelvis and rib cage to provide a stable platform for the big muscles. In a sense, as the big muscles (outer unit) become stronger and tighter, the delicate balance between the inner and outer units becomes disrupted. This concept is easier to understand using the pirate ship model (Figure 4).

The mast of the pirate ship is made of vertebra which are held together (stiffened) by the small guy wires running from vertebra to vertebra. just like the role of the multifidus (a member of the inner unit) in the human spinal column.

Although the big guy wires (representing the outer unit) are essential to hold up the mast of the pirate ship (our spine), they could never perform this function effectively if the small segmental stabilizers (inner unit) were to fail. By viewing the pirate ship's large guy wires, it becomes easy to see how developing too much tension from the overuse of exercises such as the crunch, could disrupt the posture of the mast, or spinal column in the case of a human.

To better apply the concept of the pirate ship, let's examine how the inner and outer units work in a common situation such as picking dumbbells up from the floor in the gym (Figure 5). Almost in synchrony with the thought, "Pick up the weights from the floor," the brain activates the inner unit, contracting the multifidus and drawing in the transversus abdominis. This tightens the thoraco-Iumbar fascia in a weight belt-like fashion (Figure 2). Just as this is happening, there is simultaneous activation of the diaphragm above and the pelvic floor below. The effect is to encapsulate the internal organs as they are compressed by the transversus abdominis. This process creates both stiffness of the trunk and stabilises the joints of the pelvis, spine and rib cage, allowing effective force transfer from the leg musculature, trunk and large prime movers of the back and arms to the dumbbells.

When the inner unit is functioning correctly, joint injury is infrequent, even under extreme loads such as pushing a car, tackling an opponent in football or lifting large weights in the gym. When it is not functioning correctly, activation of the large prime movers will be no different than a large wind hitting the sail of the pirate ship in the presence of loose guy wires running from vertebra to vertebra in the mast. Any system is only as strong as its weakest link!

Inner Unit Conditioning Tips

The first and most important step towards reducing back pain, improving posture and the general visual appearance, is to stop all crunch and/or sit-up type exercises until you become proficient at activating your inner unit! Although the assessment procedures for the inner unit are beyond the scope of this article, the interested reader may find detailed information in the video series "Scientific Core Conditioning". With inner unit dysfunction being extremely common in today's working and exercising population, it is safe to assume that everyone needs to start with novice exercises, even the most elite of athletes.

To begin conditioning the transversus abdominis, use the 4 Point Transversus Abdominis Trainer (Figure 6). For conditioning of the multifidus and related stabiliser and postural muscles, the Horse Stance exercises may be used (Figures 7-9).

 ALSO SEE: Core Stability: The Outer Unit.


Core Stability: The Outer Unit

By: Paul Chek.
From: IAAF/NSA 1-2.00.
Site Link: Coachr.
Article Link: The Outer Unit.


Paul Chek is an expert in the fields of corrective exercise and high performance conditioning and is the founder of the C.H.E.K Institute in San Diego, California. For over fifteen years he has traveled around the world lecturing, consulting and giving seminars. Paul Chek has been a consultant to the Los Angeles Chiropractic College, the Chicago Bulls, the Denver Nuggets, the US Army Boxing team, Australia's Canberra Raiders and the US Air Force Academy.


The author stated that abdominal exercises can be performed in various ways and asks if the common exercises really improve the functionality of the abdominal muscles. In this article the author explains first, the anatomy of the outer unit, second, he describes the function of the four sling systems of the outer unit and, finally, he demonstrates exercises targeting one or all of the sling systems in a methodical manner.

In the previous article titled The Inner Unit A New Frontier In Abdominal Training, we discussed the function of the transversus abdominis, multifidus, diaphragm and pelvic floor musculature with regard to their significant functions as stabilizers of both the spine and extremities. The main message of this article was that stabilization of the core via the inner unit must always precede force generation by the core or extremities.

The scope of this article will be, first, to explain the anatomy of the outer unit, second, to describe the function of the four sling systems of the outer unit and, finally, to demonstrate exercises targeting one or all of the sling systems in a methodical manner.   

Functional Anatomy of the outer unit

The outer unit consists primarily of phasic muscles (Table 1), although there are many muscles such as the oblique abdominals, quadratus lumborum, hamstrings and adductors which serve a dual role, acting in a tonic role as stabilizers and a phasic role as prime movers. To be technically correct, we may say that outer unit functions are predominantly phasic functions (geared toward movement).  

Superficial to the musculature of the inner unit are the outer unit systems, sometimes referred to as slings. The Deep Longitudinal System (DLS) is composed of the erector muscles of the spine and their investing fascia. The spinal erectors communicate with the biceps femoris through the sacrotuberous ligament of the pelvis and to the lower extremity via the peroneus longus muscle (Figure 1).

The Posterior Oblique System (PS) or sling consists primarily of the latissimus dorsi and the contralateral gluteus maxim us (Figure 2).    

The Anterior Oblique System (AS) consists of a working relationship between the oblique abdominal muscles and the contralateral adductor musculature and the intervening anterior abdominal fascia (Figure 3).   

The Lateral System (LS) (Figure 4) consists of a working relationship between the gluteus medius, gluteus minimus and ipsilateral adductors (1,3). Porterfield and DeRosa (3) indicate a working relationship between the gluteus medius and adductors of one leg with the opposite quadratus lumborum. The author's clinical experience strongly suggests that the oblique musculature is synergistic with the quadratus lumborum during lateral sling functions such as those seen in Figure 4.  



The deep longitudinal and posterior systems

 To better understand how the DLS and PS function, we will explore their actions in what is certainly one of our most primal movement patterns, gait (walking). While walking, there is a consistent low level activation of the inner unit muscles to provide the necessary joint stiffness to protect the joints and support the actions of the larger outer unit muscles. Recruitment of the inner unit muscles will fluctuate in intensity as needed to maintain adequate joint stiffness and support, as the inertial forces of limb movement, kinetic forces and intradiscal pressures increase.  

As we walk, we swing one leg and the opposite arm forward in what is termed counter rotation. Just prior to foot strike, the hamstrings become active . The DLS, uses the thoracolumbar fascia and paraspinal muscle system to transmit kinetic energy above the pelvis, while using the biceps femoris as a communicating link between the pelvis and lower extremity. For example, Vleeming shows that the biceps femoris communicates with the peroneus longus at the fibular head, transmitting approximately 18% of the contraction force of the biceps femoris through the fascial system into the peroneus longus.  

Interestingly, the anterior tibialis, like the peroneus longus, attaches to the plantar side of the proximal head of the first metatarsal. The significance of this relationship is appreciated when considering that there is recruitment of the biceps femoris and the anterior tibialis just prior to heel strike in concert with the peroneal muscles, which act as dynamic stabilizers of the lower leg and foot. Dorsiflexion of the foot and activation of the biceps femoris just prior to heel strike, therefore, serves to "wind up" the thoracolumbar fascia mechanism as a means of stabilizing the lower extremity and storing kinetic energy that will be released during the propulsive phase of gait (4). 

As you can see by observing Figure 2, just prior to heel strike the gluteus maximus reaches maximum stretch as the latissimus dorsi is being stretched by the forward swing of the opposite arm. Heel strike signifies transition into the propulsive phase of gait, at which time the gluteus maximus contraction is superimposed upon that of the hamstrings. Activation of the gluteus maximus occurs in concert with activation of the contralateral latissimus dorsi, which is now extending the arm in concert with the propelling leg. The synergistic contraction of the gluteus maximus and latissimus dorsi creates tension in the thoracolumbar fascia, which will be released in a pulse of energy that will assist the muscles of locomotion, reducing the metabolic cost of gait.

The anterior oblique system

The concept of the Anterior Oblique System (AS Figure 3) appears to have become popular very recently. A review of the literature shows that spiral concept of muscle-joint action was understood as integral to human movement and corrective exercise by Robert W. Lovett, M.D. and by anatomist Raymond A. Dart in the early 1900's.  

To clarify the point that movement originates in the spine (core), Gracovetsky describes torque generation by an S-shaped spinal column. He exemplifies the point that the legs are not responsible for gait, but merely instruments of expression, by showing that a man with no legs whatsoever can walk. In both the examples of what Gracovetsky calls the spinal engine, it is evident that the kinetic and potential energies of the oblique abdominal musculature, in concert with other core muscles, are primarily responsible for creating the torque that drives the spinal engine; the oblique abdominal being best situated to create rotary torque.  

The oblique abdominals, like the adductors, serve to provide stability and mobility in gait. When looking at the EMG recordings of the oblique abdominals during gait and superimposing them upon the cycle of adductor activity in gait demonstrated by Inman, it is clear that both sets of muscles contribute to stability at the initiation of the stance phase of gait, as well as to rotating the pelvis and pulling the leg through during the swing phase of gait. As the speed of walking progresses to running, activation of the anterior oblique system becomes more prominent.  

The AS is very important, particularly in sprinting, where the limbs and torso must be accelerated. The demands on the AS are great in multi-directional sports such as tennis, soccer, football, basketball and hockey. In such sporting environments the AS must not only contribute to accelerating the body, but also to changing direction and decelerating it. One need not see an EMG study to appreciate the strong contribution of the AS; just ask anyone that has experienced an abdominal strain! Accelerating, decelerating and changing directions are all activities that result in immediate pain in the presence of both abdominal and groin strains or tears.  

AS functions can be appreciated when running in sand. Because sand gives away during the initiation of the stance and propulsive phases of gait, the impulse timing of ground reaction forces is disrupted, resulting in poor use of the thoracolumbar fascia, or what Margaria calls the smart spring system. The result is that you must muscle your way through the sand. Many athletes having performed sand sprints, will note abdominal fatigue in the following day or two after the sand sprints. This is due to the increased activation of the AS to compensate for the lost kinetic, potential and muscular energy, which is usually stored and released in part by the thoracolumbar fascia system. Gracovetsky states that wearing soft soled sporting shoes, as athletes often do today, can easily disrupt the body's timing mechanism, which could very well result in increased work and may result in injury.  

During explosive activities, such as swinging a sledge hammer (Figure 5), the AS serves critical function, stabilizing as in gait, yet assisting in propelling the hammer. Trunk flexion and rotation, as a closed chain movement atop of the lead leg, is generated by the adductors as they assist in trunk flexion and internal rotation of the pelvis and assisted by gravity. Activation of the adductors occurs in concert with activation of the ipsilateal (stance leg side) internal oblique and contralateral (throwing arm side) external oblique, pulling the trunk in the necessary direction to propel the shoulder/arm complex. The forces of the shoulder/arm unit summate with those of the legs and trunk below to produce a powerful hammer swing. Here one can clearly see the phasic functions of the AS at work.

 The lateral system

Porterfield and De Rosa (3) suggest that functional anatomy dictates that the lateral system provide essential frontal plane stability. While walking, the LS will be active at heel strike (initiation of stance phase), providing frontal plane stability. This is accomplished by a force-couple action between the gluteus medius and minimus pulling the iliac crest toward the stable femur while the opposite quadratus lumborum and oblique abdominal musculature assist by elevating the ilium. This action is necessary to help create the freeway space needed to swing the leg in gait, particularly when you consider the terrain we ambulated across during developmental years. 

During functional activities such as participating in Step class (Figure 4) or simply walking up stairs (Figure 6), the LS plays a critical role, stabilizing the spine in the frontal plane. Stability in the frontal plane is very important to the longevity of the lumbar spine because frontal plane motions of the lumbar and thoracic spine are mechanically coupled with transverse plane motions; excessive amounts of either will quickly aggravate spinal joints.    

The LS provides stability that not only protects the working spinal and hip joints, but is a necessary contributor to overall stability of the pelvis and trunk. Should the trunk become unstable, the diminished stability will compromise ones ability to generate the forces necessary to move the swing leg quickly, as required by many work and sports environments. Attempts to move the swing leg, or generate force with the stance leg during gait and other functional activities, can easily disrupt the sacroiliac joints and pubic symphysis and cause kinetic dysfunction in joints throughout the entire kinetic chain.     

A classic example of distal expression of LS dysfunction was illustrated by Sahrmann. She described a lateral shift of an athlete's center of gravity over the subtalar joint while going through the stance phase of gait (Trendelenburg's Sign) resulting in an inversion ankle sprain. Since attending her course in 1992, the author has found gluteus medius weakness and contralateral low back pain due to quadratus lumborum overload common among athletes exhibiting recurring ankle sprain.  


Although the outer unit is thought of as a phasic system, (a system for moving the body) by most, it does provide crucial stabilizer functions. We must remember that the muscles of the inner unit are relatively small, with less potential to generate force than the large outer unit muscles.

The inner unit muscles are concerned with providing joint stiffness and segmental stability. They work for extended periods of time at low levels of maximal contraction. The outer unit muscles, while very well oriented for moving the body, are also very important to stability, often serving to protect the inner unit muscles, spinal ligaments and joints from damaging overload. For example, consider this common scenario:

The coach instructs two football players to engage in an oblique medicine ball toss drill. One player is much bigger and stronger than the other, as the other player finds out as he attempts to catch the 8 kg. (17.5 lbs.) medicine ball traveling at him at over 60 kph (40mph)! The smaller player does not have the strength in his outer unit to decelerate the ball and is forced into end-range trunk flexion and rotation, traumatizing his lower lumbar discs, ligaments and intrinsic spinal muscles (multifidus, rotatores, intertransversarii and interspinales).

Regardless of how well conditioned the inner unit of the smaller player may have been, lack of strength in his outer unit relative to his partner, or the demands of the task at hand resulted in inner unit overload and injury! With careful scrutiny of most activities in the work or sports environment, you will find that good eccentric strength in the outer unit systems is critical to protecting the inner unit from damage. Protection of the inner unit through proper conditioning of the outer unit is a worthy goal when one considers that optimal proprioception is dependant upon the health of the inner unit muscles and the joints they protect!   


Now that we have taken a detailed look at the anatomy and function of the outer unit, it should be clear that modern exercise technology has taken us a long way from conditioning the outer unit systems the way they were designed to work! For example, can you see any way the following exercises condition the outer unit systems in such a way that they could provide carryover to most functional work or sport activities?    

  • Crunch on Floor
  • Crunch Machines of all types
  • Sit-up
  • Hanging Leg Raises of All Types
  • Bench Press
  • Leg Press
  • Seated Row Machines?

I could go on, filling the page with exercises that do very little to enhance function. Many of you will no doubt recognize the above exercises as traditional bodybuilding exercises. What has happened? Only a few years back in the days of Bill Pearl, bodybuilders were building beautiful physiques with functional exercises like squats, lunges, barbell rows, cable rows, deadlifts and the like. Today, we are overrun by the machine era, the era of the aesthetic emotional hook so carefully used by the machine manufacturers to convince you that you will look better using their machines.    

Our bodies were not designed to exercise on machines, they were designed to function in the wild. We are designed for three-dimensional freedom, not two dimensional guided, unrealistic exercise that encourages muscle imbalance between those muscles used to stabilize and those used in a phasic manner for any given movement. The motor programs developed on machines are of little use to the body for anything other than pushing or pulling the levers of that very machine during that very exercise. This limits functional carryover to those that operate cranes, excavators, bulldozers, and buses for a living; they are about the only people that must apply force to levers in a seated, supported, two-dimensional environment.    


Using your new understanding of the outer unit systems, carefully analyze such functional pushing and pulling exercises as the single arm standing cable row (Figure 7) and standing single arm cable push (Figure 8). You will see all outer unit systems being conditioned simultaneously, jU5t as they are used in most of our work and sport environments. 



Medicine ball exercise, like free weight training, was much more popular in the 40s, 50s, 60s, and 70s than it is today. Great athletes of those decades used exercises such as the oblique medicine ball toss and push-pass, not to mention almost 100 other variations of medicine ball exercises.  

The Swiss Ball can be used to effectively condition the outer unit systems in three-dimensional movement while providing unloading opportunities for those recovering from injury. For example, analyze the Supine Lateral Ball Roll (Figure 9) and see if you can determine which outer unit systems are being used and categorize them in the order of demand during this exercise. This will be a great start toward a better understanding of functional exercise.  



The outer unit consists of four systems, the deep longitudinal, posterior oblique, anterior oblique and lateral. These systems are dependent upon the inner unit for the joint stiffness and stability necessary to create an effective force generation platform. Failure of the inner unit to work in the presence of outer unit demand often results in muscle imbalance, joint injury and poor performance. The outer unit cannot be effectively conditioned in patterns of movement that carryover to function when using modern bodybuilding machines. Effective conditioning of the outer unit should include exercises that require integrated function of the inner and outer units, using movement patterns common to any given client's work or sport environment.



Muscle Architecture, Mechanics and Specific Adaptation to Resistance Training

By: Thrasivoulos Paxinos, M.Sc., Ph.D. Athens College of Sport Sciences.
Site Link: Coachr.


Skeletal muscle represents the largest organ of the body. It makes up approximately 40% of the total body weight and it is organized into hundreds of separate entities, or body muscles, each of which has been assigned a specific task to enable the great variety of movements that are essential to normal life:
Each muscle is composed of a great number of subunits, muscle fibers, that are arranged in parallel and typically extend from one tendon to another. In order to understand the performance of muscle it is essential to know the properties of the individual fibers. With the laboratory techniques now available it is possible to study the contractile behavior of intact single fiber. The single fiber preparation offers the possibility to study the mechanical performance under strict control of sarcomere length. This is of particular importance as the sarcomere length reflects the state of overlap between the two sets of filaments that constitute the main functional elements of the contractile system.

Architecture of Muscle

The muscle fiber is composed of tightly packed subunits, myofibrils, that fill up most of the fiber volume. They contain the contractile element and are therefore the structures within the muscle that are responsible for force generation and active shortening. The basic functional unit of the myofibril is the sarcomere. Many sarcomeres packed together in series form the myofibril. The principal elements in the myofibrillar structure are two sets of filaments of different thickness that show a highly ordered, segmental arrangement that corresponds to the striated appearance of the myofibril.
1. The thicker filaments are made up of a fibrous protein, myosin (Hanson and Huxley, 1953; Hasselbach, 1953).
2. The second set of filaments are mainly built up of a globular protein, actin.

Interaction of these two filaments is the primary cause of muscle contraction and therefore force production. The degree of interaction is controlled by tropomyosin and troponin which are helicaly based on the actin filament.

Sliding Filaments Theory

Our knowledge about the structural organization of the contractile system in the form of two sets of filaments, stems from the pioneering work of H. B. Huxley and J. Hanson (Hanson and Huxley, 1953; Huxley, 1953; Huxley and Hanson, 1954). Their observation that the thick and thin filaments remain constant in length during muscle contraction, while the region of overlap between the two filaments changes with the fiber length, led these authors to suggest that muscle contraction is based on a sliding motion of the two sets of filaments. This idea has now gained general acceptance.
According to this view, the driving force for the sliding motion is generated by the myosin cross-bridges within the region where the thick and thin filaments overlap. The experimental evidence suggests that the myosin bridges make repeated contacts with adjacent thin filaments and that each such contact makes a contribution to the force developed during contraction. This occurs when the fiber is stimulated and calcium is released into the myoplasm from its storage site in the sarcoplasmic reticulum. Adenosine triphosphate offers the energy for the continuous action of the cross-bridges.

Motor Units

The smallest subunit that can be controlled is called a motor unit because it is separately innervated by a motor axon. Neurologically, the motor unit consists of:

  • A synaptic junction in the ventral root of the spinal cord
  • A motor axon, and
  • A motor end place in the muscle fibres. 

Under the control of the motor units are as few as three fibers or as many as 2000, depending on the fineness of the control required. Muscles of the fingers, face and eyes have a small number of shorter fibers in a motor unit, while the large muscles of the leg have a large number of long fibers in their motor units.

Each muscle has a finite number of motor units, each of which is controlled by a separate nerve ending. Excitation of each is an all-or- nothing event. The electrical indication is a motor unit action potential; the mechanical result is a twitch of tension. An increase in tension can therefore be accomplished in two ways:

1. By an increase in stimulation rate for that motor unit, or
2. By the excitation (recruitment) of an additional motor unit.

Recruitment of motor units follows the size principle, which states that the size of the newly recruited motor unit increases with the tension level at which it is recruited (Henneman, 1974). This means that the smallest unit is recruited first and the largest unit last. In this manner low tension movements can be achieved in finely graded steps. Conversely, those movements requiring high forces but not needing fine control are accomplished by recruiting the larger motor units. When maximum voluntary contraction is needed, all motor units will be firing at their maximum frequencies. Tension is reduced by the reverse process: successive reduction of firing rates and dropping out of the larger units first (Milner-Brown and Stein, 1975).

Two types of motor units are present in the muscle.

It must be added that there have been many criteria and varying terminologies associated with the types of motor units present in any muscle. Biochemists have used metabolic or staining measures to categorize the fiber types. Biomechanics researchers have used force (twitch) measures (Milner-Brown et, al., 1973), and electrophysiologists have used electromyographic indicators (Warmolts and Engel, 1973; Milner- Brown et, al., 1975).

Furthermore, a muscle with a higher percent- age of type II fibers reacts with shol1er electro- mechanical delay, time to peak tension and relaxation. Persons having this type of muscles, produce higher maximal speeds and a higher level of force for a cel1ain speed of contraction.

Muscle Cross-Sectional Area

Muscle force is defined as the maximum tension produced during one contraction. This is related to the number of myosin cross-bridges, in parallel formation, which are able to interact with actin and produce tension. Each cross-bridge is a separate factor of force production. When air is present and calcium passes into the fiber, the cross-bridges stal1 a cyclic procedure of attachment to actin, tension production and relaxation. This cyclic procedure is not the same for the different types of muscles (it depends on the type of the heavy meromyosin of the cross-bridges). Scientific results also show that different types of cross-bridges produce various levels of tension. Also, even during maximum contraction, only a pal1 of the whole of cross-bridges is active.
The maximum force that a muscle can generate is directly related to its cross-sectional area (Morris, 1949; Tricker and Tricker, 1967; Ikai and Fukunaga, 1970; Norman, 1977). Hypothesizing that the number of myofibrils of muscle fibers are not significantly different, cross-sectional area is an accurate way to foresee the maximum tension of the muscle.

Mechanical Model of the Muscle

Three elements compose the mechanical model of the muscle influencing its mechanical behavior and effecting contraction:

  1. The contractile element
  2. The series elastic element, and
  3. The parallel elastic element

This model could be useful in order to explain the dynamic properties of the muscle and to understand its mechanical behavior.

The contractile element represents the muscle fibers, which are the active part of the muscle and are competent to produce tension. The parallel elastic element represents the connective tissue surrounding each muscle fiber, groups of fibers and the whole of the muscle. Furthermore, the elastic element represents the elasticity of cross- bridges (Huxley, 1974). They lengthen and respond like a spring. The series elastic element refers mainly to the tendons of the muscle which are placed "in series" with the contractile and parallel elastic elements. Finally, friction is represented on the model by a viscous piston used to explain the passive viscoelastic characteristics of muscle influenced by intracellular and extracellular fluids of muscle fibers.

Types of Muscle Contraction

The term contraction can be thought of as the state of muscle when tension is generated across a number of actin and myosin filaments. Depending on the external load, its direction of action, and its magnitude, contraction has been given different names.

  1. Concentric Contraction refers to the situation in the muscle when the muscle shortens its length during contraction: at a joint the term describes the situation in which the net muscle movement is in the same direction as the change in joint angle. Utilizing concentric exercises, mechanical work is positive.

  2. In Eccentric Contraction muscle is lengthened while it is contracting. The net muscle movement is now in the opposite direction from the change in the joint angle. In eccentric exercises mechanical work is negative.

  3. Isometric Contraction refers to the condition where neither the muscle nor the joint angle changes. The corresponding mechanical work is zero.

For a muscle, eccentric contraction produces the highest tension while concentric the lowest with isometric in between.

Force-Length Relationship of the Muscle

This relationship refers to force production from the muscle depending on its initial length before contraction. According to this, the muscle produces the highest force when it starts contraction from its resting length and possibly with a small elongation. The key to the shape of the force-length curve is the changes of the structure of the myofibril at the sarcomere level (Gordon et. al., 1966). At resting length, there are a maximum number of cross-bridges between the filaments, and therefore, maximum tension is possible. As the muscle lengthens the filaments are pulled apart and the number of cross-bridges and the tension reduces to zero. As the muscle shortens to less than resting length there is an overlapping of the cross-bridges and an interference takes place. This results in a reduction of tension that continues until a full overlap occurs. The tension never drops to zero, but is drastically reduced by these interfering elements.

In the human body the starting length of the muscle is effected by the joint angles. When the joint is in full extension, the extensors are shortened while the flexors are extended. Intermediate joint angles produce different muscle lengths and different force production according to force- length relationship. This has an effect on resistance training programs especially when free weights are used.
The connective tissue that surrounds the contractile element also influences the force- length curve. It is called the parallel elastic component, and it acts much like an elastic band. When the muscle is at resting length or less, the parallel elastic component is in a slack state with no tension. As the muscle lengthens, the parallel element is no longer loose, so tension begins to build up, slowly at first, and then more rapidly. Unlike most springs, which have a linear force- length relationship, the parallel element is quite nonlinear. The passive force of the parallel element is always present, but the amount of active tension in the contractile element at any given length is under voluntary control. Thus the overall force-Iength characteristics is a function of percent of excitation. 

Series Elastic Element and Electromechanical Delay

The relative speed of elongation of the series elastic element seems to be the most important factor for the electromechanical delay observed in the muscle. It is defined as the time lag between the onset of electromyographic activity and tension in the muscle. Other factors associated with electromechanical delay are conduction of the action potential in the t-tubulus system, release of calcium from the sarcoplasmic reticu- lum and the subsequent formation of the cross- bridges between actin and myosin filaments. These events are likely to be short when com- pared to the rate of lengthening of the series elastic element, which might be the primary cause for the value of electromechanical delay in a given muscle.

In isometric contraction the force is generated through the action of contractile element on the series elastic element, which is stretched (Braun- wald et. al., 1967). Concentric contraction, where the load is attached to the end of the muscle, is always preceded by an isometric type of contraction with rearrangements of lengths of contractile and series elastic elements. The final movement begins when the pulling force of contractile element on the series elastic element equals, or slightly exceeds, that of the load.

Electromechanical delay is shorter during eccentric contraction in comparison to concentric (Komi, 1973; Komi and Cavanagh, 1977). This can partially be explained by the fact that during eccentric contraction the direction of lengthening of series elastic element is the same with the action of the contractile element. The reverse is the case for concentric contraction. This is also one of the factors for greater tension production with eccentric contraction.

Force-Velocity Relationship of the Muscle

This relationship refers to force production from the muscle according its speed of contraction. The tension in a muscle decreases as it shortens under load (concentric contraction) while the reverse is true in eccentric contraction (muscle lengthens under load).

During concentric contraction, the decrease of tension as the shortening velocity increases has been attributed to two main causes:

Such viscosity requires internal force to overcome and therefore results in a lower tendon force. There is relatively little knowledge about the details of the force-velocity curve as the muscle lengthens (eccentric contraction). Experimentally, it is somewhat more difficult to conduct experiments involving eccentric work because an external device must be available to do the work on the human muscle. The reasons given for the forces increasing as the velocity of lengthening increases are similar to those that account for the drop of tension during concentric contractions. Within the contractile element it is understood that the force required to break the cross-bridges protein links is greater than that required to hold it at its isometric length, and that this force in- creases as the rate of breaking increases. Furthermore, the viscous friction of shortening is still very much present. However, because the direction of shortening has reversed, the tendon force must now be higher in order to overcome the damping friction. 

Specific Adaptation to Resistance Training

Most of the studies exploring this area use isokinetic contraction. One of the unique features of isokinetic training is that the speed of movement may be controlled during the exercise. This is perhaps the most important feature of isokinetic training as related to sports training since, in most sports activities, muscular force is applied during movement at various speeds. The force-velocity relationship is shifted upward and to the right in athletes, particularly those whose muscles contain a high percentage of fast twitch fibers. In view of the fact that fiber type distribution cannot be changed through training, studies try to answer the question if the force-velocity curve can be shifted upward and to the right following isokinetic resistance training.

The results of these studies present the following conclusions:

Following the above conclusions, specific needs can be tackled accordingly. However, in order to shift the entire curve, fast-speed isokinetic training must be used.


Bergstrom, J. (1962) Muscle Electrolytes in Man, Scandinavian Journal of Clinical Laboratory Investigation, Suppl. 68

Braunwald, E., J. Ross and E. H. Sonnenblick (1967) Mechanisms of Contraction of Normal and Failing Heart, New England Journal of Medicine, 277: 853-863

Burke, R. E. and V. R. Edgerton (1975) Motor Unit Properties and Selective Involvement in Movement, Exer. Sports Science Review; 3: 31-81

Di Prampero, P .E. (1985) Metabolic and Circulatory Limitations to VO2max at the Whole Animal Level, Journal of Experimental Biology, 115, 319-332

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Edman, K.A.P. (1988) Double- Hyperbolic Force -Velocity Relation in Frog Muscle Fibers, Journal of Physiology, 404, 301-321

Frost, H.M. (1973) Orthopaedic Biomechanics, Charles C. Thomas, Springfield, IL

Gordon, A.M., A.F. Huxley and F. J. Julian (1966) The Variation in Isometric Tension with Sarcomere Length in Vertegrate Muscle Fibers, Journal of Physiology, 184: 170

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Hasselback, W. (1953) Elektrommikroskopische Untersuchungen and Juske!flbrillen beitota!er und partieller Extraktion des L-Myosins, Zeitschrift fur Naturforschung, 8b, 449-54

Hill, A.V. (1938) The Heat of Shortening and the Dynamic Constants of Muscle, Proc. R. Sac. Land., 126B: 136-195

Huxley, A.F. (1953) Electron-microscope Studies of the Organization of the Filaments in Striated Muscle, Biochimica et Biophysica Acta, 12, 387

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Strength Assessment

By: Matt Brzycki.
From: Coachr.

Brzycki is the coordinator of health, fitness, strength and conditioning programs at Princeton University. He has authored three books, co-authored another and written more than 180 articles on strength and fitness for 33 different publications.

Strength tests are used for a variety of populations, from professional athletes to recreational fitness enthusiasts. The main reasons for performing strength tests are to evaluate initial strength levels and to assess changes in strength. Regardless of the reason for testing muscular strength, trainers and other staff need to perform testing in a safe, efficient manner. Examined here are some traditional forms of strength testing, as well as some alternate ways to test to ensure accuracy and the test's safety.

The history of strength assessments

Strength tests and measurements began in the U.S. around 1860. At that time, the major focus was on anthropometric measurements, such as size and symmetry. Around 1880, physical testing shifted from anatomical proportions to muscular strength. Then, in the 1920s, new and more scientific test methods were developed, and statistical techniques for data analysis became available. Through the years, a few specific types of strength tests have become the most popular. 

Traditional 1-RM testing requires skill, proper warm-up, instruction, supervision and practice.

Traditional test methods

Two basic types of strength tests have evolved: static and dynamic. In a static (or isometric) test, a muscle exerts tension against a fixed, nonmoving resistance. In a dynamic (or isotonic) test, one or more body parts moves against a resistance.

Strength testing has gradually become more sophisticated. Now tests can be conducted in a formal, scientific setting - such as a laboratory or sports medicine facility with equipment ranging from relatively simple dynamometers and tensiometers to more elaborate isokinetic and motor- driven testing devices. Some equipment can even provide both static and dynamic tests that measure strength at different joint angles over a full range of motion, and then plot a "strength curve" with an incredible degree of accuracy. Unfortunately, such scientific testing can be expensive and involves a considerable amount of time. In addition, sophisticated scientific tests are usually not practical to assess a large number of individuals.

Fortunately, there is a more convenient way to assess muscular strength without the drawbacks of elaborate scientific testing. Since these easier assessments are performed outside of a formal scientific setting, they are referred to as "field tests." Field tests represent simple, convenient, easy-to-administer methods of measurement that require a minimum amount of time, cost and equipment. For these reasons, many strength and fitness professionals rely on field tests to assess muscular strength.

The most popular (and traditional) way to assess dynamic strength is to determine how much weight an individual can lift for one repetition. A one-repetition maximum (1- RM) is usually performed using three or four exercises that are representative of the body's major muscle groups. For example, a bench press or an incline press is typically used to assess the strength of the chest, shoulders and triceps, while a squat or a leg press is often used to measure the strength of the hips and legs.

Traditional 1-RM testing

The traditional way to test strength using a 1-RM raises a number of concerns. One reservation is that performing a 1-RM is a highly specialized skill, requiring proper warm-up, instruction, supervision and practice.1 In addition, traditional1-RM testing can be time-consuming, due to the number of warm-up sets that are required to prepare for the maximal attempt. These problems are magnified when evaluating a large group of people. 1,2 

Another concern with traditional1-RM testing is an increased risk of musculoskeletal injury.l,2,3,4 Attempting a 1-RM with a maximal or near-maximal weight can place an inordinate amount of stress on muscles, bones and connective tissues. Injuries occur when the stress exceeds the tensile strength of these structural components. The concern for safety increases when testing certain populations, such as younger adolescents and older adults who are at greater risk for orthopedic injury.1

Fitness professionals must identify a means to assess the muscular strength of their clients that is safe and efficient, but also inexpensive, practical and reasonably accurate.

Strength and anaerobic endurance

To discuss alternate ways to test strength, it's necessary to distinguish between strength and anaerobic endurance. In basic terms, strength is the ability to exert force, and maximal strength is a measure of the ability to exert force during a single muscular contraction with a maximal load. In contrast, anaerobic endurance is the ability to exert force during successive muscular contractions with a submaximal load. It is important not to confuse anaerobic endurance with cardiovascular endurance. Anaerobic endurance is a short-term, high-intensity muscular effort---less than about two minutes; cardiovascular endurance involves muscular effort for a much longer duration. 

Strength and anaerobic endurance are highly related.4 A review of strength-training literature indicates that there is a direct relationship between reps-to-fatigue and the percentage of maximal load (or weight): As the percentage of maximal load increases, the number of repetitions decreases in an almost linear fashion.5

Data also suggests that 10 reps-to-fatigue could be performed with a weight equal to approximately 75 percent of a maximal load.5 For example, if your 1-RM is 200 pounds, then you should be able to perform 10 reps-to-fatigue with 150 pounds (75 percent of 200). Expressed in other terms, if your maximal strength is 200 pounds, then a measure of your anaerobic endurance is your ability to perform 10 repetitions with 150 pounds before experiencing muscular fatigue. This would also be known as your 10-repetition maximum (10-RM).

Unless you have an injury or other musculoskeletal disorder, the relationship between your muscular strength and your anaerobic endurance remains relatively constant.4 Therefore, regardless of whether your strength increases or decreases, you should always be able to perform the same number of repetitions with a given percentage of your 1-RM. This also suggests that if you improve your 1-RM by 20 percent, then your 10-RM should also improve by 20 percent. Conversely, if you increase your anaerobic endurance, then you also increase your muscular strength. So, if you improve your 10-RM by 20 percent, then your 1-RM should also improve by 20 percent. Keep in mind, however, that the actual improvement in a 1-RM may be less if you haven't practiced the requisite skill in performing a 1-RM.

Implications for testing

Since there is a direct relationship between anaerobic endurance and strength, you can determine anaerobic endurance by measuring strength, and determine strength by measuring anaerobic endurance. Though it doesn't directly measure pure maximal strength, testing anaerobic endurance is much safer than attempting a 1-RM because it involves submaximal loads.

A number of prediction equations have been developed and used to estimate a 1-RM based on the relationship between strength and anaerobic endurance. While some of the equations have proven to be reasonably accurate, one problem with them is that they do not take into consideration individual differences.2,3

Genetic influences on testing Each individual inherits a different potential for improving muscular size and strength, cardiovascular' endurance, anaerobic endurance and other physical attributes. Indeed, a person's physical profile is largely determined by several inherited characteristics, including the ratio of fast-twitch (FT) to slow-twitch (ST) muscle fibers, limb length and neurological ability.

Because of these genetic influences, especially muscle fibers, some people perform either less than or more than 10 reps-to-fatigue with 75 percent of their maximal strength. Westcott reported data on 141 subjects who did a test of anaerobic endurance with 75 percent of their 1-RM.6 (Remember, it has been suggested that an individual could do 10 reps-to-fatigue with this workload.) According to the data, the subjects completed an average of 10.5 repetitions. However, only 16 of the 141 subjects (11.35 percent) did exactly 10 reps-to-fatigue with 75 percent of their 1-RM. Many of the subjects were within a few repetitions of 10. In fact, 66 of the subjects (46.81 percent) were able to do between eight and 13 reps-to-fatigue. On the other hand, 75 of the subjects (53.19 percent) did either less than eight reps-to-fatigue or more than 13. At the extremes, two subjects did only five reps-to-fatigue and one managed 24.

If predicting a 1-RM from reps-to-fatigue is to be as accurate as possible, individual differences in anaerobic endurance must be considered. There are several ways to determine an individual-specific estimate of a 1-RM.

1-RM and anaerobic endurance tests.

One way to obtain an individual-specific estimate of a 1-RM is to perform actual tests of muscular strength and anaerobic endurance. To do this, first determine the maximal weight that you can lift for one repetition using good technique. Next, assess your anaerobic endurance by taking 75 percent of your 1-RM and performing as many repetitions as possible using good technique. For instance, if your 1-RM is 200 pounds, do a set with 150 pounds (75 percent of 200). Suppose that you are able to do eight reps-to-fatigue with 75 percent of your 1- RM (instead of 10 reps-to-fatigue as has been suggested). You have just established an individual-specific relationship between your strength and anaerobic endurance based upon your inherited characteristics. More specifically, you now know that you can do eight reps-to-fatigue with 75 percent of your 1-RM. In the future, you can estimate your 1-RM based upon your inherited characteristics by dividing the most weight you can lift for eight repetitions by 0.75.

A two-set prediction equation.

Another approach to attain an individual-specific estimate of a 1-RM is to use a prediction equation. The most frequently used prediction equations are based on the reps-to-fatigue done in one set.2,3 However, a test using one set does not account for individual differences in anaerobic endurance. A better way to assess muscular strength from anaerobic endurance is to use a prediction equation that is based on the reps-to-fatigue obtained in two sets. A two-set prediction equation is shown in Figure 1.

To illustrate the equation, guesstimate a weight that will allow you to reach muscular fatigue in approximately four or five repetitions. On a later date, guesstimate a weight that will allow you to reach muscular fatigue in approximately nine or 10 repetitions. It doesn't really matter how many repetitions you do in the two sets, as long as you do not exceed 10. Now, suppose that you did five reps with 165 pounds in the first set and 10 reps with 135 pounds in the subsequent set. Inserting these values into the equation yields an individual-specific predicted 1-RM of 189 pounds.

l-RM graphing method

A final way to make an individual-specific estimate of a 1-RM is to use a graph and plot the reps-to-fatigue obtained in two sets. On a sheet of graph paper, draw a vertical line down the left-hand side of the page. Starting at the bottom of this vertical line, draw a horizontal line across the page. Label the vertical line "weight" and mark off five- or 10-pound increments; label the horizontal line "reps-to-fatigue" and mark off 10 increments, numbering them from one to 10. The intervals between the numbers on both lines must be equidistant.

Once the graph is set up, perform two sets with the same guidelines as previously stated. On the graph, plot the weight that you used and the number of reps-to-fatigue that you did in both sets. Using a ruler, connect these two points and extend this line to the left until it intersects the vertical line that designates one repetition. This extrapolation is an individual-specific estimate of your 1-RM.

An application of the graphing method appears in Figure 2. In this instance, consider again that you did 5 reps with 165 pounds and 10 reps with 135 pounds. When these two points are plotted on the graph and the line is extrapolated to the left, it yields a predicted 1-RM of 189 pounds---the same maximum that was estimated by the two-set prediction equation.

Implications for training

There is not currently any consensus on the percentage of maximal weight that is necessary to stimulate optimal gains in strength. For the moment, however, imagine that it is 75 percent. According to the study by Westcott, this workload appears to allow an average of about 10 reps-to-fatigue.6 Recall, though, that his data also showed that many individuals can do either less than or more than 10 reps-to-fatigue. These individual differences in anaerobic endurance suggest the need to customize repetition ranges to maximize the response to strength training. For example, those who cannot do more than 10 reps-to-fatigue with 75 percent of their 1-RM have a relatively low level of anaerobic endurance (and likely a high percentage of fast-twitch muscle fibers). These individuals would benefit more by training with slightly lower repetition ranges. Conversely, those who can do more than 10 reps-to-fatigue with 75 percent of their 1-RM have a relatively high level of anaerobic endurance (and likely a high percentage of slow-twitch muscle fibers). These individuals would benefit more by training with slightly higher repetition ranges. This is not to say that 75 percent is the optimal workload for stimulating increases in strength. The use of 75 percent of a 1-RM is only to illustrate the point about the need for individualized repetition ranges. 

There are also implications for pre-planned or "periodized" workouts that demand specific numbers of repetitions with certain percentages of a 1-RM. For instance, a workout might requite individuals to perform 10 repetitions with 75 percent of their 1-RM. Because of wide variations in anaerobic endurance, however, such a prescription might be far too easy for some and literally impossible for others. Therefore, pre-planned workout schedules that stipulate the same number of repetitions with a specific percentage of maximal load for everyone may be minimally effective, except for the segment of the population who have a particular level of anaerobic endurance that corresponds exactly to the specifications and parameters of the training prescription. 


1. LeSuer, D., andJ. McCormick. An alternative to 1 RM strength testing. Unpublished paper, 1993. 

2. Ware, J ., et al. Muscular endurance repetitions to predict bench press and squat strength in college football players. Journal of Strength and Conditioning Research 9: 99-103, 1995.

3. Mayhew, J., J. Prinster, J. Ware, et al. Muscular endurance repeti- tions to predict bench press strength in men of different train- ing levels. Journal of Sports Medidne and Physical Fitness 35: 108-113, 1995. 

4. Carpinelli, R.N. How much can you bench press? High Intensity Training Newsletter 5: 2-3, 1994. 

5. Sale, D.G., and D. MacDougall. Specifidty in strength training: A review for the coach and athlete. Canadian Journal of Applied Sport Sdences 6: 87-92, 1981.

6. Westcott, W. Building Strength and Stamina. Human Kinetics: Champaign, Ill., 1996.





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.


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.


"The Sports Book"; Ray Stubbs; 2009

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

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