Diet & Fitness

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 in untrained men.^1,2 Three controlled studies of untrained individuals using a combination of 6 to 10 grams per day of pyruvate and an exercise program reported greater effects on weight loss and body fat compared with those taking a placebo with the exercise program.^3,4,5 However, in a study of healthy untrained women undergoing an exercise program, supplementing with 5 grams of pyruvate twice a day had no effect on exercise performance.⁶ Studies of pyruvate supplementation on exercise performance in trained athletes have also failed to demonstrate any beneficial effect. Seven grams per day did not improve aerobic exercise performance in cyclists,⁷ and an average of 15 grams per day did not improve anaerobic performance or body composition in football players.⁸ 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.⁸

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 in untrained men.^9,10 Three controlled studies of untrained individuals using a combination of 6 to 10 grams per day of pyruvate and an exercise program reported greater effects on weight loss and body fat compared with those taking a placebo with the exercise program.^11,12,13 However, in a study of healthy untrained women undergoing an exercise program, supplementing with 5 grams of pyruvate twice a day had no effect on exercise performance.¹⁴ Studies of pyruvate supplementation on exercise performance in trained athletes have also failed to demonstrate any beneficial effect. Seven grams per day did not improve aerobic exercise performance in cyclists,¹⁵ and an average of 15 grams per day did not improve anaerobic performance or body composition in football players.¹⁶ 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.¹⁶

Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).¹⁷ However, while some studies have shown that CoQ10 improves the way the healthy body responds to exercise,¹⁸ other studies have found no improvement.^19,20,21,22 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.²³ 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 improvement or significantly poorer results in those taking CoQ10.^24,25,26

One double-blind study found that supplementation with ubiquinol (the chemically reduced form of CoQ10) in the amount of 300 mg per day for 6 weeks improved maximum power output in a group of trained athletes.²⁷

Astaxanthin is a member of the carotenoid family with strong antioxidant properties that might protect against the oxidative stress of exercise.²⁸ Animal studies also suggest a potential effect of astaxanthin on energy metabolism.^29,30 In a double-blind trial, elite soccer players who took 4 mg per day of astaxanthin for three months had lower blood measures of muscle damage and oxidative stress after a two-hour training session.³¹ However, in another double-blind trial in weight-training men, 4 mg astaxanthin per day for three weeks did not reduce either muscle soreness, muscle weakness, or blood measures of muscle damage following a bout of intense weight-lifting.³² A double-blind trial of endurance athletes found that 4 mg per day astaxanthin for four weeks shortened the time required to complete a distance cycling trial.³³ However, in another double-blind trial, endurance performance was not improved by taking 20 mg astaxanthin per day for four weeks.³⁴

Animal studies suggest that whey protein can increase gains in lean body mass resulting from exercise.³⁵ A controlled trial found that six weeks of strength training while taking 1.2 grams of whey protein per 2.2 of pounds body weight per day resulted in greater gains in lean body mass, but improved only one out of four strength tests.³⁶ Another controlled study found that people taking 20 grams per day of whey protein for three months performed better on a test of short-term intense cycling exercise than people taking a similar amount of milk protein (casein).³⁷ However, a double-blind trial found that men taking 1.5 grams per 2.2 lbs of body weight per day of predigested whey protein for 12 weeks along with a strength training exercise program gained only half as much lean body mass and had significantly smaller increases in strength compared with men using a similar amount of predigested casein along with strength training.³⁸ A controlled study of HIV-infected women found that adding whey protein to strength training exercise was no more effective than exercise alone for increasing strength or improving body composition.³⁹

Eleuthero (Eleutherococcus senticosus) supplementation may improve athletic performance, according to preliminary Russian research.⁴⁰ Other studies have been inconclusive and two recent double-blind studies showed no beneficial effect on endurance performance in trained men.^41,42,43 Eleuthero strengthens the immune system and thus might reduce the risk of post-exercise infection. Although some doctors suggest taking 1 to 4 ml (0.2 to 0.8 tsp) of fluid extract of eleuthero three times per day, evidence supporting the use of this herb to enhance athletic performance remains weak.

AAKG (arginine alpha-ketoglutarate) is a compound made from the amino acid L-arginine and alpha-ketoglutarate (AKG) a substance formed in the body’s energy-generating process. It has been speculated that AAKG may increase production in muscles of nitric oxide, a substance known to have blood-flow-enhancing effects. A double-blind study gave trained weight lifters either 4 grams of AAKG or a placebo three times a day during an eight-week weight-training regimen. AAKG had no effect on body composition but did improve measures of strength and short-term power performance.⁴⁴

Casein protein is more slowly digested than other animal proteins, resulting in a slower yet more prolonged rise in blood levels of amino acids.⁴⁵ This has led to speculation that casein may support protein synthesis by the body for a longer period of time compared with proteins, such as whey protein, that are more rapidly digested. However, in two double blind trials, measurements of muscle protein synthesis after leg exercises were similar whether casein or whey protein (either 20 grams or 0.3 grams per 2.2 lbs body weight taken one hour after exercise) was consumed. Other double blind studies have shown that adding protein supplements to a weight-training program improves gains in muscle mass and strength, but only one trial has compared using casein alone to other proteins for improving body composition and muscle strength. In this controlled trial, overweight men were given a low-calorie diet along with a weight training exercise plan for three months. Men who followed this plan and also took 1.5 grams per day of predigested casein protein per 2.2 lbs body weight gained more strength and lean body mass, and lost more body fat than did men using a similar amount of whey protein along with the same diet and exercise plan.

In a double-blind trial, supplementation with a probiotic preparation reduced the frequency of upper respiratory tract infections in training athletes during the winter.⁴⁶ The product used in the study was fermented milk that contained 6.5 billion live Lactobacillus casei Shirota organisms, given twice a day for 16 weeks. Further research is needed to determine whether other probiotic strains would have the same effect.

Chromium, primarily in a form called chromium picolinate, has been studied for its potential role in altering body composition. Preliminary research in animals and humans suggested that chromium picolinate might increase fat loss and lean muscle tissue gain when used with a weight-training program.^47,48,49 However, most studies have found little to no effect of chromium on body composition or strength.^{50,51,52,53,54} One group of researchers has reported significant reductions in body fat in double-blind trials using 200 to 400 mcg per day of chromium for six to twelve weeks in middle-aged adults,^55,56 but the methods used in these studies have been criticized.⁵¹

Magnesium deficiency can reduce exercise performance and contribute to muscle cramps, but sub-optimal intake does not appear to be a problem among most groups of athletes.^57,58 Controlled trials suggest that magnesium supplementation might improve some aspects of physiology important to sports performance in some athletes,^59,60 but controlled and double-blind trials focusing on performance benefits of 212 to 500 mg per day of magnesium have been inconsistent.^{61,62,63,64,65,66} It is possible that magnesium supplementation benefits only those who are deficient or who are not highly trained athletes. ^66,58

Extensive but often poorly designed studies have been conducted on the use of Asian ginseng (Panax ginseng) to improve athletic performance.^67[REF] While some early controlled studies suggested there might be benefits, several recent double-blind trials have found no significant effects of Asian ginseng on endurance exercise.^68,69[REF] In many studies, it is possible that ginseng was used in insufficient amounts or for an inadequate length of time; a more effective regimen for enhancing endurance performance may be 2 grams of powdered root per day or 200 to 400 mg per day of an extract standardized for 4% ginsenosides, taken for eight to twelve weeks.^[REF] Short-term intense exercise has also not been helped by Asian ginseng according to double-blind trials,^70,71 but one controlled study reported increased pectoral and quadricep muscle strength in non-exercising men and women after taking 1 gram per day of Asian ginseng for six weeks.⁷²



An extract of a related plant, American Gingseng (Panax quinquefolius), was found ineffective at improving endurance exercise performance in untrained people after one week’s supplementation in a double-blind study.^[REF] Standardized extracts of American ginseng, unlike Asian ginseng, are not known. However, dried root powder, 1–3 grams per day in capsule or tablet form, can be used. Some herbalists also recommend 3–5 ml of tincture three times per day.

Ribose is a type of sugar used by the body to make the energy-containing substance adenosine triphosphate (ATP). Intense exercise depletes muscle cells of ATP as well as the ATP precursors made from ribose,^73,74 though these deficits are typically replaced within minutes.⁷⁵ Unpublished reports suggested that ribose supplementation might increase power during short, intense bouts of exercise.^76,77 However, in a double-blind study, exercisers took four grams of ribose four times per day during a six-day strength-training regimen, and no effects on muscle power or ATP recovery in exercised muscles were found.⁷⁸ In two other controlled studies, either 10 grams of ribose per day for five days or 8 grams every 12 hours for 36 hours resulted in only minor improvements in some measures of performance during repetitive sprint cycling.^79,80

The ability of yohimbine, a chemical found in yohimbe bark, to stimulate the nervous system,^81,82 promote the release of fat from fat cells,^83,84 and affect the cardiovascular system ⁸⁵ has led to claims that yohimbe might help athletic performance or improve body composition. However, a double-blind study of men who were not dieting reported no effect of up to 43 mg per day of yohimbine on weight or body composition after six months.⁸⁶ No research has tested yohimbe herb for effects on body composition, and no human research has investigated the ability of yohimbine or yohimbe to affect athletic performance. Other studies have determined that a safe daily amount of yohimbine is 15 to 30 mg.⁸⁷ However, people with kidney disorders should not take yohimbe, and side effects of nausea, dizziness, or nervousness may occur that necessitate reducing or stopping yohimbe supplementation.

In one 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.⁸⁸

Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^89,90 Athletes who do not eat an optimal diet, especially those who are trying to control their weight or use fad diets while exercising strenuously, may become deficient in zinc to the extent that performance or health is compromised.^91,92 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.⁹³ Whether these women were zinc deficient was not determined in this study. A double-blind study of male athletes with low blood levels of zinc found that 20 mg per day of zinc improved the flexibility of the red blood cells during exercise, which could benefit blood flow to the muscles.⁹⁴ No other studies of the effects of zinc supplementation in exercising people have been done. A safe amount of zinc for long-term use is 20 to 40 mg per day along with 1 to 2 mg of copper. Higher amounts should be taken only under the supervision of a doctor.

L-carnitine, which is normally manufactured by the human body, has been popular as a potential ergogenic aid (i.e., having the ability to increase work capacity), because of its role in the conversion of fat to energy.⁹⁵ 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 L-carnitine per day on performance have produced inconsistent results.⁹⁶ L-carnitine may be effective in certain intense exercise activities leading to exhaustion,⁹⁷ but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,^98,99 anaerobic performance,¹⁰⁰ or lean body mass in weight lifters.¹⁰¹

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.¹⁰² 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).^103,104 Controlled trials using very large amounts of MCT (approximately 85 grams over two hours) have resulted in both increased and decreased performance,^105,106 while a double-blind trial found that 60 grams per day of MCT for two weeks had no effect on endurance performance.¹⁰⁷ A controlled study found increased performance when MCTs were added to a 10% carbohydrate solution,¹⁰⁵ but another study found no advantage of adding MCT,¹⁰⁹ and a third trial actually reported decreased performance with this combination, probably due to gastrointestinal distress, in athletes using MCTs.¹⁰⁶

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);¹⁰⁹ athletic performance can suffer if these slightly increased needs are not met.¹¹⁰ However, most athletes obtain enough B vitamins from their diet without supplementation,¹¹¹ and supplementation studies have found no positive effect on performance measures for vitamin B2,^112,113 vitamin B3 (niacin),¹¹⁴ or vitamin B6.¹¹⁵ On the contrary, large amounts of niacin have been shown to impair endurance performance.¹¹⁴

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.¹¹⁶ However, most studies have found aspartic acid useless in improving either athletic performance or the body’s response to exercise.^{117,118,119,120,121}

Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^122,123 Athletes who do not eat an optimal diet, especially those who are trying to control their weight or use fad diets while exercising strenuously, may become deficient in zinc to the extent that performance or health is compromised.^124,125 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.¹²⁶ Whether these women were zinc deficient was not determined in this study. A double-blind study of male athletes with low blood levels of zinc found that 20 mg per day of zinc improved the flexibility of the red blood cells during exercise, which could benefit blood flow to the muscles.¹²⁷ No other studies of the effects of zinc supplementation in exercising people have been done. A safe amount of zinc for long-term use is 20 to 40 mg per day along with 1 to 2 mg of copper. Higher amounts should be taken only under the supervision of a doctor.

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.^128,129 Controlled human research has reported that 5.6 to 7.2 grams per day of CLA produces only non-significant gains in muscle size and strength in experienced and inexperienced weight-training men.^130,131,132 A double-blind study of a group of trained men and women reported reduced body fat in the upper arm after 12 weeks of supplementation with 1.8 grams per day of CLA.¹³³ Further research using more accurate techniques for measuring body composition is needed to confirm these findings.

Researchers have found that the amino acids in hydrolyzed protein supplements are highly available for muscle repair after muscle fiber damaging exercise and other causes of muscle injury.¹³⁴ Some, but not all, studies show that protein supplements may help athletes by reducing soreness and speeding recovery after exercise, and increasing muscle mass gains.¹³⁵ Hemp protein has lower levels than soy and egg proteins of branched-chain amino acids, which are especially important for muscle growth and repair.¹³⁶

In one study, mice fed hemp protein had more stamina and reduced lactic acid levels after exertion than mice fed other sources of protein.¹³⁷ Muscle soreness and fatigue tend to increase in the conditions that produce high levels of lactic acid.¹³⁸ The effect of hemp protein on stamina and muscle function in athletes, however, has not been studied.

Some protein supplements (particularly from whey) have been linked to increased muscle building in athletes and more efficient repair of muscle injuries after exercise.^139,140 The branched-chain amino acids in egg protein appear to be well used by muscle tissue after exercise, but researchers found that athletes taking 20 grams of egg protein or more after a workout were not able to use all of the protein and instead increased the excretion of protein breakdown products by the kidneys.¹⁴¹ In another study, supplementing with 15 grams of egg protein per day for 8 weeks did not have any effect on muscle mass or function in adult female athletes.¹⁴² A preliminary study found that post-exercise fatigue was unaffected by up to 20 grams of egg protein prior to exercise in long-distance runners.¹⁴³

AKG (alpha-ketoglutarate) is used by cells during growth and in healing from injuries and other wounds,¹⁴⁴ and is especially important in the healing of muscle tissue.¹⁴⁵ A controlled study found that intravenous AKG prevented a decline in protein synthesis in the muscles of patients recovering from surgery.^146,147 For these reasons, it has been speculated that oral AKG supplements might help improve strength or muscle-mass gains by weight lifters, but no research has been done to test this theory.

Pea protein is a good source of branched-chain amino acids (leucine, isoleucine, and valine),¹⁴⁸ which are needed for muscle building and repair.¹⁴⁹ Researchers have found that the amino acids in hydrolyzed protein supplements are highly available for muscle repair after muscle fiber damaging exercise and other causes of muscle injury.¹⁵⁰ Some, but not all, studies show that protein supplements may help athletes by reducing soreness and speeding recovery after exercise, and increasing muscle mass gains.¹⁵¹ Whether pea protein has advantages over other protein supplements for athletes has not yet been determined.

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.¹⁵² 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.¹⁵³ 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.¹⁵⁴

Deer antler base has a long history of use in Chinese medicine, and deer antler extract is being studied to determine its potential as a way to improve athletic performance.^155,156 The extract is purported to contain insulin-like growth factor 1 (IGF-1), which is a banned substance for many professional athletic competitions.

Capsaicin ointment, applied four times per day over painful joints in the upper or lower limbs, reduces pain caused by osteoarthritis,¹⁵⁷ and a plaster containing capsaicin applied to the low back for several hours per day provided relief from chronic low back pain in one study.¹⁵⁸ Other uses of cayenne or capsaicin for sports and fitness have not been studied.

Extracts of Tribulus terrestris (puncture vine) have been reported in preliminary studies to affect anabolic hormones in men.¹⁵⁹ However, a double-blind trial found no effect of 1.5 mg per day of tribulus per pound of body weight on improving body composition or strength performance results from an eight-week strength training program.¹⁶⁰

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 patients and elderly people,^161,162 no studies on muscle growth in athletes using OKG have been published.

Methoxyisoflavone is a member of the family flavonoids (isoflavones). In a U.S. Patent, the developers of this substance claim, based on preliminary animal research, that it possesses anabolic (muscle-building and bone-building) effects without the side effects seen with either androgenic (male) hormones or estrogenic (female) hormones.¹⁶³ A preliminary controlled trial found that strength-training athletes who took 800 mg per day of methoxyisoflavone for eight weeks experienced a significantly greater reduction in percentage body fat than those who took a placebo.¹⁶⁴ Double-blind research is needed to confirm these findings. The U.S. patent also claims methoxyisoflavone reduces appetite and lowers blood cholesterol levels. Whether this claim is true has not yet been demonstrated in published scientific research.

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.¹⁶⁵ 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.¹⁶⁶

Eucalyptus-based rubs have been found to warm muscles in athletes.¹⁶⁷ This suggests that eucalyptus may help relieve minor muscle soreness when applied topically, though studies are needed to confirm this possibility.

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

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

Compared with other protein supplements, rice protein has more of the amino acid arginine, and since arginine is a vasodilator that can enhance blood flow to tissues, some athletes believe rice protein may also improve blood flow to muscle to enhance growth and repair. However, no research has investigated the effects of rice protein on athletic performance.

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 amount of supplemental antioxidants that might otherwise be needed for protection. However, at least theoretically, supplements of antioxidant vitamins may be beneficial for older or untrained people or athletes who are undertaking an especially vigorous training protocol or athletic event.^168,169

Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day for several days before and after intense exercise may reduce pain and speed up muscle strength recovery.^170,171,172 However, taking vitamin C only after such exercise was not effective in another double-blind study.¹⁷³ While some research has reported that vitamin E supplementation in the amount of 800 to 1,200 IU per day reduces biochemical measures of free radical activity and muscle damage caused by strenuous exercise,^174,175,176 several studies have not found such benefits,^{177,178,179,180} and no research has investigated the effect of vitamin E on performance-related measures of strenuous exercise recovery. A combination of 90 mg per day of coenzyme Q10 and a very small amount of vitamin E did not produce any protective effects for marathon runners in one double-blind trial,¹⁸¹ 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.¹⁸²

In most well-controlled studies, exercise performance has not been shown to improve following supplementation with vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.^183,184 Similarly, vitamin E has not benefited exercise performance, ^185,186 except possibly at high altitudes. ^187,188

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 amount of supplemental antioxidants that might otherwise be needed for protection. However, at least theoretically, supplements of antioxidant vitamins may be beneficial for older or untrained people or athletes who are undertaking an especially vigorous training protocol or athletic event.^189,190

Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day for several days before and after intense exercise may reduce pain and speed up muscle strength recovery.^191,192,193 However, taking vitamin C only after such exercise was not effective in another double-blind study.¹⁹⁴ While some research has reported that vitamin E supplementation in the amount of 800 to 1,200 IU per day reduces biochemical measures of free radical activity and muscle damage caused by strenuous exercise,^195,196,197 several studies have not found such benefits,^{198,199,200,201} and no research has investigated the effect of vitamin E on performance-related measures of strenuous exercise recovery. A combination of 90 mg per day of coenzyme Q10 and a very small amount of vitamin E did not produce any protective effects for marathon runners in one double-blind trial,²⁰² 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.²⁰³

In most well-controlled studies, exercise performance has not been shown to improve following supplementation with vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.^204,205,206 Similarly, vitamin E has not benefited exercise performance, ^207,208 except possibly at high altitudes. ^209,210

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.^211,212 Creatine supplementation increases phosphocreatine levels in muscle, especially when accompanied by exercise or carbohydrate intake.^213,214 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.²¹⁵

Over 40 double-blind or controlled studies have found creatine supplementation (typically 136 mg per pound of body weight per day or 15 to 25 grams per day for five or six days) improves performance of either single or repetitive bouts of short-duration, high-intensity exercise lasting under 30 seconds each.^{216,217,218,219,220,221,222} Examples of this type of exercise include weightlifting; sprinting by runners, cyclists, or swimmers; and many types of athletic training regimens for speed and power. About 15 studies did not report enhancement by creatine of this type of performance. These have been criticized for their small size and other research design problems, but it is possible that some people, especially elite athletes, are less likely to benefit greatly from creatine supplementation.²¹⁶

Fewer studies have investigated whether creatine supplementation benefits continuous high-intensity exercise lasting 30 seconds or longer. Five controlled studies have found creatine beneficial for this type of exercise,²¹⁶ but one study found no benefit on performance of a military obstacle course run.²¹⁹ Most studies of endurance performance have found no advantage of creatine supplementation, except perhaps for non-weight bearing exercise such as cycling. ^216,218,222

Long-term use of creatine supplementation is typically done using smaller daily amounts (2 to 5 grams per day) after an initial loading period of several days with 20 grams per day. Very little research has been done to investigate the exercise performance effects of long-term creatine supplementation. One study reported that long-term creatine supplementation improved sprint performance.²¹⁸ Four controlled long-term trials using untrained women,²³⁰ trained men,²³¹ or untrained older adults found that creatine improved gains made in strength and lean body mass from weight-training programs.^232,233 However, two controlled trials found no advantage of long-term creatine supplementation in weight-training football players.^234,235

Creatine supplementation appears to increase body weight and lean body mass or fat-free mass, but these measurements do not distinguish between muscle growth and increased water content of muscle.^215,216 A few double-blind studies using more specific muscle measurements have been done and found that combining creatine supplementation with strength training over several weeks does produce greater increases in muscle size compared with strength training alone.^238,231,240

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.^231,232 Creatine supplementation increases phosphocreatine levels in muscle, especially when accompanied by exercise or carbohydrate intake.^233,234 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.²³⁵

Over 40 double-blind or controlled studies have found creatine supplementation (typically 136 mg per pound of body weight per day or 15 to 25 grams per day for five or six days) improves performance of either single or repetitive bouts of short-duration, high-intensity exercise lasting under 30 seconds each.^{236,237,238,239,240,241,242} Examples of this type of exercise include weightlifting; sprinting by runners, cyclists, or swimmers; and many types of athletic training regimens for speed and power. About 15 studies did not report enhancement by creatine of this type of performance. These have been criticized for their small size and other research design problems, but it is possible that some people, especially elite athletes, are less likely to benefit greatly from creatine supplementation.²³⁶

Fewer studies have investigated whether creatine supplementation benefits continuous high- intensity exercise lasting 30 seconds or longer. Five controlled studies have found creatine beneficial for this type of exercise,²³⁶ but one study found no benefit on performance of a military obstacle course run.²³⁹ Most studies of endurance performance have found no advantage of creatine supplementation, except perhaps for non-weight bearing exercise such as cycling. ^236,238,242

Long-term use of creatine supplementation is typically done using smaller daily amounts (2 to 5 grams per day) after an initial loading period of several days with 20 grams per day. Very little research has been done to investigate the exercise performance effects of long-term creatine supplementation. One study reported that long-term creatine supplementation improved sprint performance.²³⁸ Four controlled long-term trials using untrained women,²⁵⁰ trained men,²⁵¹ or untrained older adults found that creatine improved gains made in strength and lean body mass from weight-training programs.^252,253 However, two controlled trials found no advantage of long-term creatine supplementation in weight-training football players.^254,255

Creatine supplementation appears to increase body weight and lean body mass or fat-free mass, but these measurements do not distinguish between muscle growth and increased water content of muscle.^235,236 A few double-blind studies using more specific muscle measurements have been done and found that combining creatine supplementation with strength training over several weeks does produce greater increases in muscle size compared with strength training alone.^258,251,260

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,²⁵¹ nor do they improve exercise performance or enhance the effects of physical training.^{252,253,254,255,256,257} However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes and prolonging endurance performance in the heat.^258,259 One controlled study gave triathletes 6 grams per day of BCAA for one month before a competition, then 3 grams per day from the day of competition until a week following. Compared with a placebo, BCAA restored depleted glutamine stores and immune factors that occur in elite athletes, and led to a reported one-third fewer symptoms of infection during the period of supplementation.²⁶⁰ Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.^261,253,263

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,²⁶³ nor do they improve exercise performance or enhance the effects of physical training.^{264,265,266,267,268,269} However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes and prolonging endurance performance in the heat.^270,271 One controlled study gave triathletes 6 grams per day of BCAA for one month before a competition, then 3 grams per day from the day of competition until a week following. Compared with a placebo, BCAA restored depleted glutamine stores and immune factors that occur in elite athletes, and led to a reported one-third fewer symptoms of infection during the period of supplementation.²⁷² Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.^273,265,275

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 amount of supplemental antioxidants that might otherwise be needed for protection. However, at least theoretically, supplements of antioxidant vitamins may be beneficial for older or untrained people or athletes who are undertaking an especially vigorous training protocol or athletic event.^275,276

Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day for several days before and after intense exercise may reduce pain and speed up muscle strength recovery.^277,278,279 However, taking vitamin C only after such exercise was not effective in another double-blind study.²⁸⁰ While some research has reported that vitamin E supplementation in the amount of 800 to 1,200 IU per day reduces biochemical measures of free radical activity and muscle damage caused by strenuous exercise,^281,282,283 several studies have not found such benefits,^{284,285,286,287} and no research has investigated the effect of vitamin E on performance-related measures of strenuous exercise recovery. A combination of 90 mg per day of coenzyme Q10 and a very small amount of vitamin E did not produce any protective effects for marathon runners in one double-blind trial,²⁸⁸ 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.²⁸⁹

In most well-controlled studies, exercise performance has not been shown to improve following supplementation with vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.^290,291 Similarly, vitamin E has not benefited exercise performance, ^292,293 except possibly at high altitudes. ^294,295

The use of alkalinizing agents, such as sodium bicarbonate, sodium citrate, and phosphate salts (potassium phosphate, sodium acid phosphate, and tribasic sodium phosphate) to enhance athletic performance is designed to neutralize the acids produced during exercise that may interfere with energy production or muscle contraction.²⁹⁶ Some double-blind studies, though not all, have found that sodium bicarbonate or sodium citrate typically improves exercise performance for events lasting either 1 to10 minutes or 30 to 60 minutes.^{297,298,299,300,301,302,303,304[REF]} The amounts used are 115 to 180 mg of sodium bicarbonate or 135 to 225 mg of sodium citrate per pound of body weight. These amounts are dissolved in at least two cups of fluid and are taken either as a single ingestion at least one hour before exercise or divided into smaller amounts and taken over several hours before exercise. Performance during periods of less than one minute or between 10 and 30 minutes is not improved by taking alkalinizing agents.^{305,306,307,302,304} Sodium citrate may be preferable to sodium bicarbonate because it causes less gastrointestinal upset.138 Another alkalinizing agent, phosphate salts, has been investigated primarily as an endurance performance enhancer, with very inconsistent results.^310,311

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.³¹⁰ Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.³¹¹ Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,³¹² an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,³¹³ and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.³¹⁴ However, glutamine supplementation (30 mg per 2.2 pounds body weight) has not improved performance of short-term, high-intensity exercise such as weightlifting or sprint cycling by trained athletes,^315,316 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,^317,318 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.³¹⁹

Many athletes do not eat an optimal diet, especially when they are trying to control their weight while training strenuously.³²⁰ These athletes may experience micronutrient deficiencies that, even if marginal, could affect performance or cause health problems.^{321,322,323,324} 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.^325,326,327

Very little research has been done to evaluate the ergogenic effects of most vitamins or minerals other than those discussed in this article. Supplementation with selenium (180 mcg per day for 10 weeks) had no effect on the results of endurance training in one double-blind trial.³²⁸ 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.³²⁹ The importance of other individual vitamins and minerals is discussed elsewhere in this section.

At very high intakes (approximately 250 mg per 2.2 pounds of body weight), the amino acid arginine has increased growth hormone levels,³³⁰ an effect that has interested body builders due to the role of growth hormone in stimulating muscle growth.³³¹ 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.³³² 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.³³³ High amounts of arginine or ornithine do not appear to raise levels of insulin,^334,335 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.^336,337

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,³³⁸ resulted in higher total strength and lean body mass, and reduced evidence of tissue breakdown after only five weeks.³³⁹

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.^340,341,342 However, anemia in athletes is often not due to iron deficiency and may be a normal adaptation to the stress of exercise.³⁴² 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 doctor. Athletes who are found to be iron deficient by a physician are typically given 100 mg per day until blood tests indicate they are no longer deficient. Supplementing iron-deficient athletes with 100 to 200 mg per day of iron increased aerobic exercise performance in some,^344,345,346 though not all,^347,348 double-blind studies. A recent double-blind trial found that iron-deficient women who took 20 mg per day of iron for six weeks were able to perform knee strength exercises for a longer time without muscle fatigue compared with those taking a placebo.³⁴⁹

Extensive but often poorly designed studies have been conducted on the use of Asian ginseng (Panax ginseng) to improve athletic performance.^349,350 While some early controlled studies suggested there might be benefits, several recent double-blind trials have found no significant effects of Asian ginseng on endurance exercise.^351,352,350 In many studies, it is possible that ginseng was used in insufficient amounts or for an inadequate length of time; a more effective regimen for enhancing endurance performance may be 2 grams of powdered root per day or 200 to 400 mg per day of an extract standardized for 4% ginsenosides, taken for eight to twelve weeks.³⁵⁴ Short-term intense exercise has also not been helped by Asian ginseng according to double-blind trials,^355,356 but one controlled study reported increased pectoral and quadricep muscle strength in non-exercising men and women after taking 1 gram per day of Asian ginseng for six weeks.³⁵⁷ An extract of a related plant, American ginseng (Panax quinquefolius), was found ineffective at improving endurance exercise performance in untrained people after one week’s supplementation in a double-blind study.^[REF]

HMB (beta hydroxy-beta-methylbutyrate) is a metabolite (breakdown product) of leucine, one of the essential branched-chain amino acids.  Biochemical and animal research show that HMB has a role in protein synthesis and might, therefore, improve muscle growth and overall body composition when given as a supplement. However, double-blind human research suggests that HMB may only be effective when combined with an exercise program in people who are not already highly trained athletes. Double-blind trials found no effect of 3 to 6 grams per day of HMB on body weight, body fat, or overall body composition in weight-training football players or other trained athletes.^{357,358,359,360,361} However, one double-blind study found that 3 grams per day of HMB increased the amount of body fat lost by 70-year old adults who were participating in a strength-training program for the first time.³⁶² A double-blind study of young men with no strength-training experience reported greater improvements in muscle mass (but not in percentage body fat) when HMB was used in the amount of 17 mg per pound of body weight per day.³⁶³ However, another group of men in the same study given twice as much HMB did not experience any changes in body composition.

An animal study found reduced blood measures of muscle damage after strenuous exercise when the animals were fed tart cherry juice prior to exercise.³⁶⁴ In a small, double-blind study, young men drank 12 ounces twice daily of tart cherry juice blended with apple juice [note: ratio not given in study], equivalent to 80 mg per day of anthocyanins or 100 to 120 cherries per day. After eight days the men performed intense elbow flexion exercises, and after drinking tart cherry juice this exercise resulted in less muscle pain and loss of strength compared to after drinking a placebo juice.³⁶⁵ In a small double-blind study, trained athletes took about one ounce twice daily of a tart cherry juice concentrate, containing about 550 mg per day of anthocyanin, for ten days beginning seven days before an intense session of weight-training leg exercises. Compared to when they took a placebo concentrate, taking tart cherry concentrate resulted in faster recovery of leg muscle strength after the exercise.³⁶⁶ Two double-blind trials investigated the effects of tart cherry juice in long distance runners. In one small double-blind trial,³⁶⁷ drinking eight ounces twice daily of tart cherry juice blended with apple juice, [note: ratio not given] equivalent to 80 mg per day of anthocyanins or 100 to 120 cherries per day, for eight days beginning five days before a marathon resulted in faster recovery of leg muscle strength and smaller elevations in post-race blood measures of inflammation. However, there was no difference in muscle soreness or in post-race blood measures of muscle damage. In another, larger double-blind trial,³⁶⁶ long distance runners who drank 10.5 ounces twice daily of tart cherry juice blended with apple juice, [note: ratio not given] equivalent to 80 mg per day of anthocyanins or 100 to 120 cherries per day, for eight days beginning one week before the race reported only one-third as much post-race muscle pain compared to those who used a placebo juice.

Dehydroepiandrosterone (DHEA) is a hormone produced by the adrenal glands that is used by the body to make the male sex hormone testosterone. In one double-blind trial, 100 mg per day of DHEA was effective for improving strength in older men,³⁶⁸ but 50 mg per day was ineffective in a similar study of elderly men and women.³⁶⁹ DHEA has not been effective for women or younger men in other studies.^370,371

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.³⁷² Nonetheless, commercial sports drinks containing sodium and potassium may help to replace electrolytes lost in sweating during prolonged exercise, and will often make it easier to drink adequately as well as to retain more fluid.³⁷³

Some athletes participating in several hours of exercise have developed a potentially dangerous condition called hyponatremia (low blood sodium levels) even when electrolyte-containing sports drinks were used.³⁷⁴ This condition may be caused by fluid retention due to excessive drinking combined with natural reductions in kidney function during exercise, so some authorities caution against overdrinking during exercise, especially if the exerciser notices that his or her body weight goes up after prolonged physical activity.³⁷³

In one preliminary study, elderly men participating in a 12-week strength training program took a liquid supplement containing 10 grams of protein (part of which was soy protein), 7 grams of carbohydrate, and 3 grams of fat either immediately following exercise or two hours later.³⁷⁵ Men taking the supplement immediately following exercise experienced significantly greater gains in muscle growth and lean body mass than those supplementing two hours later, but strength gains were no different between the two groups. A controlled study of female gymnasts found that adding 0.45 grams of soy protein (0.45 grams per pound of body weight per day) to a diet that was adequate in protein during a four-month training program did not improve lean body mass compared with a placebo.³⁷⁶ No research has compared different sources of protein to see whether one source, such as soy protein, has a better or more consistent effect on exercise recovery or the results of strength training.

In a double-blind study of active young men, supplementation with 750 of soybean-derived phosphatidylserine per day for 10 days increased the time the men could exercise until exhaustion by approximately 25%.³⁷⁷ Longer studies are needed to determine whether this effect would persist with continued supplementation.

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).³⁷⁸ 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.

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).³⁷⁹ 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.

In a double-blind study of trained athletes, the incidence of upper respiratory tract infections following a three-day period of intensive exercise was significantly lower in people who took quercetin than in those who received a placebo (5% versus 45%).³⁸⁰ The amount of quercetin used was 500 mg twice a day, beginning three weeks before, and continuing for two weeks after, the intensive exercise.

In a double-blind trial, healthy volunteers received 200 mg of an extract of Rhodiola rosea (standardized to contain 3% rosavin plus 1% salidroside) or a placebo one hour prior to an endurance-exercise test. Compared with placebo, rhodiola significantly increased endurance, as measured by the time it took to become exhausted.^[REF] However, after daily use of rhodiola for four weeks, the herb no longer enhanced short-term endurance. Consequently, if rhodiola is being considered as an exercise aid, it should be used only occasionally.