Athletic Performance

Also indexed as: Endurance, Exercise, Sports Supplements, Training

Aside from training, nutrition may be the most important influence on athletic performance.1 However, in seeking a competitive edge, athletes are often susceptible to fad diets or supplements that have not been scientifically validated. Nevertheless, there is much useful research to guide the exerciser toward optimum health and performance.

Checklist for Athletic Performance

Rating Nutritional Supplements Herbs
3Stars Citrate (for high-intensity, short- to intermediate-duration exercise)
Iron (for iron deficiency only)
Sodium bicarbonate (for high-intensity, short- to intermediate-duration exercise)		  
2Stars Creatine monohydrate (for high-intensity, short duration exercise or sports with alternating low- and high-intensity efforts)
Electrolyte replacement (for ultra-endurance competition only)
Glutamine (for reducing risk of post-exercise infection)
Vitamin C (if deficient, or to reduce pain and speed up muscle strength recovery after intense exercise)
Vitamin E (for exercise recovery and high-altitude exercise performance only)		 Asian ginseng
Eleuthero
1Star Arginine/Ornithine (for body composition and strength)
Beta-sitosterol/Beta-sitosterol glucoside (in combination for reducing the risk of post-exercise infection)
Branched-chain amino acids (for high altitude and extreme temperature only, for reducing the risk of post-exercise infection, or for preventing decline of mental functioning during exercise)
Chromium
CLA
Coenzyme Q10
Copper
Gamma oryzanol
HMB (for strength and body composition)
L-carnitine (see text)
Magnesium
Medium chain triglycerides
Octacosanol
Phosphorus
Pyruvate
Vitamin B-complex
Zinc		 American ginseng
Ephedra
Eucalyptus (topical)
Guaraná
Kola
See also:  Homeopathic Remedies for Athletic Performance
3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star An herb is primarily supported by traditional use, or the herb or supplement has little scientific support and/or minimal health benefit.

How is it treated? Conventional therapy for improved athletic performance is to ensure adequate and balanced nutrition, sufficient fluid intake, and proper rest. The avoidance of performance-reducing drugs such as alcohol and tobacco is also commonly recommended.

Dietary changes that may be helpful: Calorie requirements for athletes depend on the intensity of their training and performance. The athlete who trains to exhaustion on a daily basis needs more fuel than one who performs a milder regimen two or three times per week. Calorie requirements can be as much as 23 to 39 calories per pound of body weight per day for the training athlete who exercises vigorously for several hours per day.2 3 Many athletes compete in sports having weight categories (such as wrestling and boxing), sports that favor small body size (such as gymnastics and horse racing), or sports that may require a specific socially accepted body shape (such as figure skating). These athletes may feel pressured to restrict calories to extreme degrees to gain a competitive edge.4 Excessive calorie restriction can result in chronic fatigue, sleep disturbances, reduced performance, impaired ability for intensive training, and increased vulnerability to injury.5

The carbohydrates are the most efficient fuel for energy production and can also be stored as glycogen in muscle and liver, functioning as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for sports performance.6 Depending on training intensity and duration, athletes require up to 4.5 grams of carbohydrates per day per pound of body weight or 60 to 70% of total dietary calories from carbohydrates, whichever is greater.7 8 Emphasizing grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement beverages, along with reducing intake of fatty foods, results in a relatively high-carbohydrate diet.

Carbohydrate beverages should be consumed during endurance training or competition (30 to 70 grams of carbohydrate per hour) to help prevent carbohydrate depletion that might otherwise occur near the end of the exercise period. At the end of endurance exercise, body carbohydrate stores must be replaced to prepare for the next session. This replacement can be achieved most rapidly if 40 to 60 grams of carbohydrate are consumed right after exercise, repeating this intake every hour for at least five hours after the event.9 Standard sport drinks containing 6 to 8% carbohydrates can be used during exercise, while high-density carbohydrate beverages containing 20 to 25% carbohydrate are useful for immediate post-exercise repletion. Addition of protein or a blend of essential amino acids to these products, may increase their effectiveness for carbohydrate repletion,10 may help athletes recover from anaerobic (short-term and intense) exercise,11 and, according to preliminary research,12 13 may facilitate muscle growth during weight training.

Carbohydrate-loading, or “super-compensation,” is a pre-event strategy that improves performance for some endurance athletes.14 15 Carbohydrate-loading can be achieved by consuming a 70% carbohydrate diet (or 4.5 grams per pound of body weight) for three to five days before competition, while gradually reducing training time, and ending with a day of no training while continuing the diet until the event date.

Protein requirements are often higher for both strength and endurance athletes, than for people who are not exercising vigorously; however, the increased food intake needed to supply necessary calories and carbohydrates also supplies extra protein. As long as the diet contains at least 12 to 15% of calories as protein, or up to 0.75 grams per day per pound of body weight, protein supplements are neither necessary, nor likely, to be of benefit.16 17 The very high-protein diets sometimes used by body builders may impair kidney function by increasing blood pressure. A preliminary study of male athletes consuming at least 2.77 grams per pound of body weight per day showed no evidence of kidney impairment; however, the study was limited to one month, and evidence of long-term kidney problems associated with chronic protein loading were not examined.18

Some athletes have speculated that consuming a high-fat diet for two or more weeks prior to endurance competition might cause the body to shift its fuel utilization toward more abundant fat stores (“fat adaptation”). In general, high-fat diets have not been found to consistently improve performance and may even be detrimental;19 20 21 however, one study did report that a high-fat diet supported endurance training and performance as effectively as a high-carbohydrate diet did after two to four weeks of adaptation to the diets.22

Water is the most abundant substance in the human body and is essential for normal physiological function. Water loss due to sweating during exercise can result in decreased performance and other problems. Fluids should be consumed prior to, during, and after exercise, especially when extreme conditions of climate, exercise intensity, and exercise duration exist.23 Approximately two glasses of fluid should be consumed two hours before exercise and at regular intervals during exercise; fluid should be cool, not cold (59 to 72° F, 15 to 22.2° C). Flavored sports drinks containing electrolytes are not necessary for fluid replacement during brief periods of exercise, but they may be more effective in encouraging the athlete to drink frequently and in larger amounts.24

Lifestyle changes that may be helpful: Many athletes use exercise and weight-modifying diets as tools to change their body composition, assuming that a lower percentage of body fat and/or higher lean body mass is desirable in any sport. There is no single standard for body weight and body composition that applies to all types of athletic activities. Different sports, even different roles in the same sport (e.g., running vs. blocking in football), require different body types. These body types are largely determined by genetics. However, within each athlete’s genetic predisposition, variations result from diet and exercise that may affect performance. In general, excess weight is a disadvantage in activities that require quickness and speed. However, brief, intense bursts of power depend partly on muscle size, so this type of activity may favor athletes with greater muscle mass. On the other hand, participants in endurance sports, which require larger energy reserves, should not attempt to lower their body fat so much as to compromise their performance.25

Nutritional supplements that may be helpful: Iron is important for an athlete because it is a component of hemoglobin, which transports oxygen to muscle cells. Some athletes, especially women, do not get enough iron in their diet. In addition, for reasons that are unclear, endurance athletes, such as marathon runners, frequently have low body-iron levels.26 27 28 However, anemia in athletes is often not due to iron deficiency and may be a normal adaptation to the stress of exercise.29 Supplementing with iron is usually unwise unless a deficiency has been diagnosed. People who experience undue fatigue (an early warning sign of iron deficiency) should have their iron status evaluated by a physician.

The use of alkalinizing agents, such as sodium bicarbonate, sodium citrate, and phosphorus, to enhance athletic performance is designed to neutralize the acids produced during exercise that may interfere with energy production or muscle contraction.30 Placebo-controlled studies have found that sodium bicarbonate typically improves exercise performance for events lasting one to seven minutes when 135 mg per pound of body weight is used.31 This amount is dissolved in at least two cups of fluid and is taken either as a single ingestion at least one hour before exercise or divided into smaller amounts and taken over several hours before exercise. Similarly, improved exercise performance of short to intermediate duration has been reported for sodium citrate ingestion at 225 mg per pound of body weight in placebo-controlled studies.32 33 34 35 However, performance during periods of less than one minute36 37 38 or greater than seven minutes is not improved by taking alkalinizing agents.39 40 Sodium citrate may be preferable to sodium bicarbonate because it causes less gastrointestinal upset.41 Another alkalinizing agent, phosphorus, has been investigated primarily as an endurance performance enhancer, with very inconsistent results.42 43

In most well-controlled studies, exercise performance has not been shown to benefit from supplementation of vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.44 45 Similarly, vitamin E has not benefited exercise performance,46 except possibly at high altitudes.47 48

Most research has demonstrated that strenuous exercise increases production of harmful substances called free radicals, which can damage muscle tissue and result in inflammation and muscle soreness. Exercising in cities or smoggy areas also increases exposure to free radicals. Antioxidants, including vitamin C and vitamin E, neutralize free radicals before they can damage the body, so antioxidants may aid in exercise recovery. Regular exercise increases the efficiency of the antioxidant defense system, potentially reducing the increased intake otherwise needed for protection. However, at least theoretically, supplements of antioxidant vitamins may be beneficial in older or untrained people or athletes who are undertaking an especially vigorous training protocol or athletic event, although research focusing on recovery from exercise is lacking.49 50

Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day may reduce pain and speed up muscle strength recovery after intense exercise.51 52 Reductions in blood indicators of muscle damage and free radical activity have also been reported for supplementation with 400 to 1,200 IU per day of vitamin E in most studies,53 54 55 but no measurable benefits in exercise recovery have been reported.56 A combination of 90 mg per day of coenzyme Q10 and a very small amount of vitamin E did not produce any protective effects in one double-blind trial,57 while in another double-blind trial, a combination of 50 mg per day of zinc and 3 mg per day of copper significantly reduced evidence of post-exercise free radical activity.58

Electrolyte replacement is not as important as water intake in most athletic endeavors. It usually takes several hours of exercise in warm climates before sodium depletion becomes significant and even longer for depletions of potassium, chloride, and magnesium to occur.59 However, the presence of sodium in fluids will often make it easier to drink as well as to retain more fluid.60

The amino acid, glutamine, appears to play a role in several aspects of human physiology that might benefit athletes, including their muscle function and immune system.61 Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.62 Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,63 an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,64 and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.65 However, glutamine supplementation (30 mg per 2.2 pounds body weight) has not improved performance of short-term, high-intensity exercise by trained athletes,66 and no studies on endurance performance or muscle growth have been conducted. Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,67 68 double-blind trials giving athletes glutamine (5 grams after intense, prolonged exercise, then again two hours later) reported 81% having no subsequent infection compared with 49% in the placebo group.69

Creatine (creatine monohydrate) is used in muscle tissue for the production of phosphocreatine, a factor in the formation of ATP, the source of energy for muscle contraction and many other functions in the body.70 71 Creatine supplementation increases phosphocreatine levels in muscle, especially when accompanied by exercise or carbohydrate intake.72 73 It may also increase exercise-related gains in lean body mass, though it is unclear how much of these gains represents added muscle tissue and how much is simply water retention.74 Most,75 76 though not all,77 78 controlled studies have shown that taking 20 grams per day of creatine monohydrate for five or six days by sedentary or moderately active people, has improved performance and delayed muscle fatigue during short-duration, high-intensity exercise, such as sprinting and weight lifting.

Creatine supplementation has improved athletic performance of trained athletes in competitive situations, as reported in some,79 80 81 but not all,82 83 84 studies. Very little research has been done to investigate the exercise performance effects of long-term (over one month) creatine supplementation. Two controlled long-term trials using untrained women85 or trained men86 found that creatine improved gains made in strength and lean body mass from weight-training programs. However, a third preliminary trial found only insignificant gains from creatine supplementation in weight-training football players.87 In one study, creatine supplementation not only failed to increase endurance performance but may have impaired it by contributing to weight gain.88

The B-complex vitamins are important for athletes, because they are needed to produce energy from carbohydrates. Exercisers may have slightly increased requirements for some of the B vitamins, including vitamin B2, vitamin B6, and vitamin B5 (pantothenic acid);89 athletic performance can suffer if these slightly increased needs are not met.90 However, most athletes obtain enough B vitamins from their diet without supplementation,91 and supplementation studies have found no effect on performance measures for vitamin B2,92 93 vitamin B3 (niacin),94 or vitamin B6.95

Chromium, primarily in a form called chromium picolinate, has been studied for its potential role in altering body composition. Preliminary research in animals96 and humans97 98 suggests that chromium picolinate increases fat loss and lean muscle tissue gain when used with a weight-training program. However, several recent studies have found little to no effect of chromium on body composition or strength,99 100 101 though one group of researchers has reported significant reductions in body fat measured with precise techniques in double-blind trials using 200 to 400 mcg per day of chromium for six to twelve weeks in middle-aged adults.102 103

Magnesium deficiency can reduce exercise performance and contribute to muscle cramps, but it is not clear whether the occasional sub-optimal intake found in some athletes is particularly important.104 One clinical trial found no effect of supplementation with 500 mg per day of magnesium on performance or muscle symptoms in athletes with blood levels of magnesium in the low end of the normal range.105 However, two double-blind studies have reported intriguing results. One suggested that magnesium at 3.6 mg per pound body weight per day (including both diet and supplements) may benefit strength training,106 and the other trial used 390 mg per day of magnesium in triathletes and demonstrated improved swimming, cycling, and running times.107

Some research has shown that supplemental branched-chain amino acids (BCAA) (typically 10 to 20 grams per day) do not result in meaningful changes in body composition,108 nor do they improve exercise performance109 110 111 112 or enhance the effects of physical training.113 114 However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes,115 restoring depleted glutamine stores and immune factors that occur in elite athletes,116 and prolonging endurance performance in the heat.117 Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.118 119 120

L-carnitine, which is normally manufactured by the human body, has been popular as a potential ergogenic (i.e., having the ability to increase work) aid because of its role in the conversion of fat to energy.121 However, while some studies have found that L-carnitine improves certain measures of muscle physiology, research on the effects of 2 to 4 grams of carnitine per day on performance have produced inconsistent results.122 L-carnitine may be effective in certain intense exercise activities leading to exhaustion,123 but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,124 125 anaerobic performance,126 or lean body mass in weight lifters.127

At very high intakes (approximately 250 mg per 2.2 pounds of body weight), the amino acid, arginine, has increased growth hormone levels,128 an effect that has interested body builders due to the role of growth hormone in stimulating muscle growth.129 However, at lower amounts recommended by some manufacturers (5 grams taken 30 minutes before exercise), arginine failed to increase growth hormone release and may even have impaired the release of growth hormone in younger adults.130 Large quantities (170 mg per 2.2 pounds of body weight per day) of a related amino acid, ornithine, have also raised growth hormone levels in some athletes.131 High amounts of arginine132 or ornithine133 do not appear to raise levels of insulin, another anabolic bodybuilding hormone. More modest amounts of a combination of these amino acids have not had measurable effects on any anabolic hormone levels during exercise.134 135

Nonetheless, double-blind trials conducted by one group of researchers, combining weight training with either arginine and ornithine (500 mg of each, twice per day, five times per week) or placebo, found the amino-acid combination produced decreases in body fat,136 resulted in higher total strength and lean body mass, and reduced evidence of tissue breakdown after only five weeks.137

Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).138 However, the effects of CoQ10 on how the healthy body responds to exercise have been inconsistent, with several studies finding no improvement.139 140 A few studies, using at least four weeks of CoQ10 supplementation at 60 to 100 mg per day, have reported improvements in measures of work capacity ranging from 3 to 29% in sedentary people and from 4 to 32% in trained athletes.141 However, recent double-blind and/or placebo-controlled trials in trained athletes, using performance measures such as time to exhaustion and total performance, have found either no significant improvement142 or significantly poorer results in those taking CoQ10.143 144

One group of researchers in two small, controlled trials has reported that 100 grams of a combination of dihydroxyacetone and pyruvate enhanced the endurance of certain muscles.145 146 More recently, evidence has appeared casting doubt on the ability of high levels (an average exceeding 15 grams per day depending upon body weight) of pyruvate to improve exercise capacity in a weight-lifting study.147

Gamma oryzanol is a mixture of sterols and ferulic acid esters. Despite claims that gamma oryzanol or its components increase testosterone levels, stimulate the release of endorphins, and promote the growth of lean muscle tissue, research has provided little support for these claims and has also shown gamma-oryzanol to be poorly absorbed.148 A recent nine-week, double-blind trial of 500 mg per day of gamma-oryzanol in weight lifters found no benefit compared with placebo in strength performance gains or circulating anabolic hormones.149 However, a small, double-blind trial using 30 mg per day of ferulic acid for eight weeks in trained weight lifters did find significantly more weight gain (though lean body mass was not measured) and increased strength in one of three measures compared with placebo.150

Medium chain triglycerides (MCT) contain a class of fatty acids found only in very small amounts in the diet; they are more rapidly absorbed and burned as energy than are other fats.151 For this reason, athletes have been interested in their use, especially during prolonged endurance exercise. However, no effect on carbohydrate sparing or endurance exercise performance has been shown with moderate amounts of MCT (30 to 45 grams over two to three hours).152 153 Controlled trials using very large amounts of MCT (approximately 85 grams over two hours) have resulted in both increased154 and decreased performance.155 A controlled study found increased performance when MCTs were added to a 10% carbohydrate solution,156 but another study actually reported decreased performance with this combination, probably due to gastrointestinal distress, in athletes using MCTs.157

Wheat germ oil, which contains a waxy substance known as octacosanol, has been investigated as an ergogenic agent. Preliminary studies have suggested that octacosanol improves endurance, reaction time, and other measures of exercise capacity.158 In another preliminary trial, supplementation with 1 mg per day of octacosanol for eight weeks improved grip strength and visual reaction time, but it had no effect on chest strength, auditory reaction time, or endurance.159

HMB (beta hydroxy-beta-methylbutyrate) is a metabolite (breakdown product) of leucine, one of the essential branched-chain amino acids. As with other amino acid-related substances, HMB appears to play a role in the synthesis of protein, including the protein that builds new muscle tissue. Animal research suggests that HMB may improve the growth of lean muscle tissue,160 but only preliminary and limited research in humans supports the potential link between HMB and enhanced muscle building161 or endurance performance162 in athletes. One controlled trial of people involved in a weight-lifting program reported that supplements of 3 grams of HMB, compared with no supplementation, contributed to greater gains of muscle mass and strength in seven weeks.163 However, double-blind trials have found no effect of 3 to 6 grams per day of HMB for four weeks on body composition or exercise performance in athletes.164 165 166

Conjugated linoleic acid (CLA) is a slightly altered form of the essential fatty acid, linoleic acid. Animal research suggests an effect of CLA supplementation on reducing body fat.167 168 Limited placebo-controlled human research found 5.6 to 7.2 grams per day of CLA produced only non-significant gains in muscle size and strength in experienced169 and inexperienced170 weight-training men.

Beta-sitosterol, (BSS) a natural sterol found in many plants, has been shown in a double-blind trial to improve immune function in marathon runners when combined with a related substance called B-sitosterol glucoside (BSSG).171 This implies that beta-sitosterol might reduce infections in athletes who engage in intensive exercise, though studies are still needed to prove this. The usual amount of this combination used in research is 20 mg of BSS and 200 mcg of BSSG three times per day.

Inosine is a nucleic acid derivative that appears in exercising muscle tissue. Its role in various cellular reactions has led to suggestions that it may have ergogenic effects.172 However, two placebo-controlled studies demonstrated no beneficial effects on performance and suggested that inosine may impair some aspects of exercise performance.173 174 Therefore, use of inosine is discouraged.

Caffeine is present in many popular beverages and appears to have an effect on fat utilization.175 Caffeine does not benefit short-term, high-intensity exercise, according to most,176 177 but not all, studies.178 179 However, placebo-controlled research, much of it double-blind, has shown that endurance performance does appear to be enhanced by caffeine in many athletes.180 181 182 183 Inconsistency in reported effectiveness of caffeine in some trials can be explained by differences in caffeine sensitivity among athletes, variable effect of caffeine on different forms of exercise and under different environmental conditions, and effects of other dietary components on the response to caffeine.184 185 Effective amounts of caffeine appear to be about 2.5 mg per pound of body weight, which would require 2 to 3 cups brewed coffee, or the equivalent, taken one hour before exercise. However, most research has used caffeine supplements in capsules, and a recent study found caffeine was not effective when taken as coffee.186 Caffeine consumption is banned by the International Olympic Committee at levels that produce urinary concentrations of 12 mg/ml or more. These levels would require ingestion of considerably more than 2.5 mg per pound of body weight, or several cups of coffee, over a short period of time.187

Androstenedione (andro) is an androgen hormone. It is produced in the adrenal glands and gonads from dehyroepiandrosterone (DHEA) or 17 alpha-hydroxyprogesterone, and is converted to testosterone by several tissues, including muscle. One study reported that 100 mg of andro raised testosterone levels in women to six times the normal range and was significantly more effective in this than a similar amount of DHEA.188 A German patent claims that oral androstenedione briefly raises blood levels of testosterone in men.189 One double-blind trial found an initial rise in testosterone in men taking androstenedione, but then a gradual decline to previous levels despite continued supplementation, suggesting that the body may compensate for the effects of androstenedione by decreasing its own natural production of testosterone.190 In controlled studies, andro supplementation at 300 mg per day raised both testosterone and estrogen in one trial with men,191 but raised only estrogen in another.192 Lesser amounts of 100 mg per day raised estrogen in both of these studies but had no effect on testosterone levels. Strength or muscle mass gains were measured in one of these studies,193 but no benefit was found from 300 mg per day of andro during an eight-week weight-training regimen. A double-blind trial examining the effect of 200 mg of androstenedione or androstenediol (another male hormone that converts to testosterone in the body) in older men found no significant changes in testosterone at the end of a 12-week, high-intensity weight-training program. Other findings included a lack of measurable advantage of androstenedione supplementation on muscle strength or body composition, increases in estrogen levels, a lowering of HDL (“good”) cholesterol, and less exercise-induced protection from age-related diseases in men taking androstenedione.194

Many athletes do not eat an optimal diet, especially when they are trying to control their weight while training strenuously.195 These athletes may experience micronutrient deficiencies that, even if marginal, could affect performance or cause health problems.196 197 198 199 However, athletes who receive recommended daily allowances of vitamins and minerals from their diet do not appear to benefit from additional multivitamin-mineral supplements with increased performance.200 201 202 The importance of individual vitamins and minerals is discussed elsewhere in this section.

Very little research has been done to evaluate the ergogenic effects of most vitamins or minerals. Supplementation with selenium (180 mcg per day for 10 weeks) had no effect on the results of endurance training in one double-blind trial.203 Vanadyl sulfate, a form of vanadium that may have an insulin-like action, was given to weight-training athletes in a double-blind trial, using 225 mcg per pound of body weight per day, but no effect on body composition was seen after 12 weeks, and effects on strength were inconsistent.204

Certain amino acids, the building blocks for protein, might be ergogenic aids as discussed below. However, while athletes have an increased need for protein compared with non-exercising adults, the maximum amount of protein suggested by many researchers—0.75 grams per pound of body weight—is already in the diet of most athletes as long as they are not restricting calories. Supplements of amino acids are therefore not needed to fulfill protein requirements for either strength or endurance exercise.205

Aspartic acid is a non-essential amino acid that participates in many biochemical reactions relating to energy and protein. Preliminary, though conflicting, animal and human research suggested a role for aspartic acid (in the form of potassium and magnesium aspartate) in reducing fatigue during exercise.206 However, most studies have found aspartic acid useless in improving either athletic performance or the body’s response to exercise.207 208 209 210 211

Whey protein is a dairy-based source of amino acids. While whey is a high-quality source of protein, there is no current evidence supporting its use for strength training or body building.

Ornithine alpha-ketoglutarate (OKG) is formed from the amino acids ornithine and glutamine and is believed to facilitate muscle growth by enhancing the body’s release of anabolic hormones. While this effect has been found in studies on hospitalized patients212 and elderly people,213 no studies on muscle growth in athletes using OKG have been published.

Are there any side effects or interactions? Refer to the individual supplement for information about any side effects or interactions.

Herbs that may be helpful: Extensive but often poorly-executed studies have been conducted on the use of Asian ginseng (Panax ginseng) to improve athletic performance.214 Some of these studies have reported that Asian ginseng is beneficial,215 while others have not.216 One study also found that an extract of a related plant, American ginseng (Panax quinquefolius), was not effective at improving exercise performance in untrained people after one week’s supplementation.217 Despite a lack of consistent evidence, some doctors recommend taking extracts containing 5% ginsenosides at a level of 150 to 200 mg three times per day for at least several weeks. Because Asian and American ginseng both affect the immune system, they might also be helpful for reducing the risk of infection after strenuous exercise, though this has not been studied.

Eleuthero (Eleutherococcus senticosus) supplementation may improve athletic performance, according to preliminary Russian research.218 Other studies have been inconclusive219 or have shown no beneficial effect.220 Eleuthero strengthens the immune system and thus might reduce the risk of post-exercise infection. Although many doctors suggest taking 1 to 4 ml (0.2 to 0.8 tsp) of fluid extract of eleuthero three times per day, supportive evidence remains weak.

Some athletes take guaraná during their training; however, there is no scientific research to support this use. Guaraná contains caffeine, which is discussed above. Another caffeine-containing herb sometimes used during training is kola nut.

Ma huang (ephedra) has been used to improve training performance, and the herb and its alkaloids, ephedrine and pseudoephedrine, are banned by the International Olympic Committee.221 When taken with caffeine, ephedra has been shown to increase energy during high-intensity, aerobic-exercise performance.222 However, the amount of combined caffeine (375 mg) and ephedrine (75 mg) used in this study produced nausea and vomiting in 25% of participants. While lower amounts of the caffeine/ephedrine combination may have similar effects on energy without the associated side effects,223 there are known long-term health consequences for both caffeine and ephedrine. Anyone with high blood pressure, heart conditions, diabetes, glaucoma, hyperthyroidism, anxiety or restlessness, impaired circulation to the brain, benign prostatic hyperplasia with residual urine accumulation, or pheochromocytoma (primary adrenal tumor), as well as those taking MAO-inhibiting antidepressants, digitoxin, or guanethidine should avoid this combination. Others wishing to enhance athletic performance should consult with a qualified sports therapist.

Eucalyptus-based rubs have been found helpful compared to placebo, for warming muscles in athletes.224 This also suggests eucalyptus may help relieve minor muscle soreness when applied topically, though studies are needed to confirm this possibility.

Are there any side effects or interactions? Refer to the individual herb for information about any side effects or interactions.

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