Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).¹⁰ However, while some studies have shown that CoQ10 improves the way the healthy body responds to exercise,¹¹ other studies have found no improvement.^12,13,14,15 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.¹⁶ 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.^17,18,19

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.²⁰

Eleuthero(Eleutherococcus senticosus) supplementation may improve athletic performance, according to preliminary Russian research.²¹ Other studies have been inconclusive and two recent double-blind studies showed no beneficial effect on endurance performance in trained men.^22,23,24 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.

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.^27,28 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.^29,30,31 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.³² 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,³³ and an average of 15 grams per day did not improve anaerobic performance or body composition in football players.³⁴ 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.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

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.^68,69 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.^70,71,72 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.⁷³ Further research using more accurate techniques for measuring body composition is needed to confirm these findings.

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.⁷⁴

Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^75,76 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.^77,78 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.⁷⁹ 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.⁸⁰ 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.

Some protein supplements (particularly from whey) have been linked to increased muscle building in athletes and more efficient repair of muscle injuries after exercise.^83,84 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.⁸⁵ 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.⁸⁶ 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.⁸⁷

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.⁸⁹ 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.⁹⁰ 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.⁹¹

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.⁹² 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.⁹³ Hemp protein has lower levels than soy and egg proteins of branched-chain amino acids, which are especially important for muscle growth and repair.⁹⁴

In one study, mice fed hemp protein had more stamina and reduced lactic acid levels after exertion than mice fed other sources of protein.⁹⁵ Muscle soreness and fatigue tend to increase in the conditions that produce high levels of lactic acid.⁹⁶ The effect of hemp protein on stamina and muscle function in athletes, however, has not been studied.

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.⁹⁷ 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.⁹⁸ L-carnitine may be effective in certain intense exercise activities leading to exhaustion,⁹⁹ but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,^100,101 anaerobic performance,¹⁰² or lean body mass in weight lifters.¹⁰³

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.¹²³ 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.¹²⁴

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,^125,126 no studies on muscle growth in athletes using OKG have been published.

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,^131,132 though these deficits are typically replaced within minutes.¹³³ Unpublished reports suggested that ribose supplementation might increase power during short, intense bouts of exercise.^134,135 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.¹³⁶ 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.^137,138

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.

Extracts of Tribulus terrestris (puncture vine) have been reported in preliminary studies to affect anabolic hormones in men.¹³⁹ 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.¹⁴⁰

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);¹⁴¹ athletic performance can suffer if these slightly increased needs are not met.¹⁴² However, most athletes obtain enough B vitamins from their diet without supplementation,¹⁴³ and supplementation studies have found no positive effect on performance measures for vitamin B2,^144,145 vitamin B3 (niacin),¹⁴⁶ or vitamin B6.¹⁴⁷ On the contrary, large amounts of niacin have been shown to impair endurance performance.¹⁴⁶

The ability of yohimbine, a chemical found in yohimbe bark, to stimulate the nervous system,^148,149 promote the release of fat from fat cells,^150,151 and affect the cardiovascular system ¹⁵² 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.¹⁵³ 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.¹⁵⁴ 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.

Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^155,156 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.^157,158 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.¹⁵⁹ 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.¹⁶⁰ 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.