Conditions:
Sports Performance

Principal Proposed Treatments
  • Repetitive, High-Intensity, Short-Burst Exercise, Creatine (Creatine Monophosphate), Strength and Power, (Hydroxymethyl Butyrate) HMB, Post-Race Infection, Muscle Soreness, Vitamin C
Other Proposed Treatments
  • ERGOGENIC AIDS:  Alpha-Ketoglutarate (OKG), Amino Acids, Arginine, Branched Chain Amino Acids (BCAAs), Caffeine, Carnitine, Chromium, Ciwujia, Coenzyme Q10, Conjugated Linoleic Acid (CLA), Cordyceps, Dihydroxyacetone Pyruvate (DHAP), Gamma Oryzanol, Ginseng, Glutamine, Guarana, Inosine, Ipriflavone, Iron, Lipoic Acid, Magnesium, Ma Huang (Ephedra), Medium-Chain Triglycerides, Nicotinamide Adenine Dinucleotide (NADH), Policosanol, Ornithine, Pantothenic Acid/Pantethine, Phosphate, Phosphatidylserine (PS), Protein Hydrosylates, Protein Supplements (Soy or Whey Powder), Ribose, Schisandra, Suma, Tribulus terrestris, Trimethylglycine (TMG), Vitamin B1 (Thiamin), Vitamin B2 (Riboflavin), Vitamin B3 (Niacin), Vitamin B6 (Pyridoxine)
  • SUPPLEMENTS FOR RECOVERY:  Beta-Carotene, Bromelain, Glucosamine, Glutamine, Horse Chestnut, Oligomeric Proanthocyanidins (OPCs), Selenium, Thymus Extract, Vitamin E
Not Recommended Treatments
  • Androstenedione, Dehydroepiandrosterone (DHEA), Vanadium, Boron

In the competitive world of sports, the smallest advantage can make an enormous difference in the outcome of a contest. A supplement that could improve an athlete's strength, speed, or endurance could make the difference between tenth and first place in a race. Supplements that could enhance the training process or shorten the time to heal from an injury would also be enormously valuable to serious athletes. Because of this, sports supplements are a big business, and many athletes try to enhance their abilities by using them.

A supplement that can improve an athlete's performance is called an "ergogenic aid"—but the big question is, "Are there really any ergogenic aids?" Proper training, good nutrition, and a healthy lifestyle definitely increase performance, but the case for supplements is much weaker. Some evidence suggests that the supplement creatine might improve performance in repetitive, short-burst, high-intensity exercise, as well as possibly enhance resistance training. Similarly, hydroxymethyl butyrate (HMB) might help bodybuilders and strength athletes. On another note, vitamin C might help prevent post-marathon respiratory infections.

However, many other sports supplements are available for sale with no more than the scantiest evidence behind them, or none at all; of these, some present safety risks.

In this article, we explore the many supplements used in hopes of improving sports performamance. For information on treating sports injuries, see the full article on that topic.

Principal Proposed Treatments for Sports Performance

In this section, we discuss sports supplements with some real evidence behind them: creatine, HMB, vitamin C, and sports beverages. Each has its own recommended use for athletes. We also address nutrition and training, the best-established ergogenic aids of all.

Creatine: Ergogenic Aid For Repetitive, High-Intensity, Short-Burst Exercise and, perhaps, Resistance Exercise 

Creatine is one of the best-selling and best-documented supplements for enhancing athletic performance, although the scientific evidence that it works is still far from complete. The evidence that does exist points to benefits in forms of exercise that require repeated short-term bursts of high-intensity exercise, such as soccer and basketball.^1–4 Creatine has also been proposed to promote weight loss and reduce the proportion of fat to muscle in the body, but there is little evidence that it is effective for these purposes.⁵

Creatine is a naturally occurring substance that plays an important role in the production of energy in the body: the body converts it to phosphocreatine, a form of stored energy used by muscles. In theory, taking supplemental creatine will build up a reserve of phosphocreatine in the muscles, to help them perform on demand. Supplemental creatine may also help the body make new phosphocreatine faster when it has been used up by intense activity.

Creatine is not an essential nutrient because your body can make it from the amino acids L-arginine, glycine, and L-methionine. Provided that you eat enough protein (the source of these amino acids), your body will make all the creatine you need for good health. However, because meat is the most important dietary source of creatine and its amino acid building blocks, vegetarian athletes may potentially have difficulty producing enough creatine themselves.

What Is the Scientific Evidence for Creatine?

Several small double-blind studies suggest that creatine can improve performance in exercises that involve repeated short bursts of high-intensity activity.⁶ The evidence is better for men than for women.

A double-blind study investigated creatine and swimming performance in 18 men and 14 women.⁷ Men taking the supplement had significant increases in speed when doing 6 bouts of 50-meter swims started at 3-minute intervals, as compared with men taking placebo. However, their speed did not improve when swimming 10 sets of 25-yard lengths started at 1-minute intervals. It may be that the shorter rest time between laps was not enough for the swimmers' bodies to resynthesize phosphocreatine.

Interestingly, none of the women enrolled in the study showed any improvement with the creatine supplement. The authors of this study noted that women normally have more creatine in their muscle tissue than men do, so perhaps creatine supplementation (at least at this level) is not of benefit to women, as it appears to be for men. Further research is needed to fully understand this gender difference in response to creatine.

In an earlier double-blind study, 16 physical education students exercised 10 times for 6 seconds on a stationary cycle, alternating repetitions with a 30-second rest period.⁸ The results showed that individuals who took 20 g of creatine for 6 days were better able to maintain cycle speed throughout the repetitions. Many other studies showed similar improvements in performance capacity involving repeated bursts of action,^9,10,11  although there have been negative results as well.^12–17

In contrast, studies of endurance or nonrepetitive exercise have not shown benefits from creatine supplementation.^18–22 Therefore, creatine probably won't help you with marathon running or single sprints.

Isometric exercise capacity (pushing against a fixed resistance), however, may improve with creatine.^23,24,230 In addition, two double-blind, placebo-controlled studies, each lasting 28 days, provide some evidence that creatine and creatine plus HMB can increase lean muscle and bone mass.²⁵ The first enrolled 52 college football players during off-season training, and the other followed 40 athletes engaged in weight training.

For more information, including dosage and safety issues, see the full creatine article.

HMB: Ergogenic Aid For Strength and Power Athletes

Technically "beta-hydroxy beta-methylbutyric acid," HMB is a chemical that occurs naturally in the body when the amino acid leucine breaks down.

Leucine is found in particularly high concentrations in muscles. During athletic training, damage to the muscles leads to the breakdown of leucine as well as increased HMB levels. Evidence suggests that taking HMB supplements might signal the body to slow down the destruction of muscle tissue.³⁹ However, while promising, the research record at present is contradictory and marked by an absence of large studies.

HMB is not an essential nutrient, so there is no established requirement. HMB is found in small amounts in citrus fruit and catfish. To get a therapeutic dosage, however, you need to take a supplement in powder or pill form.

What Is the Scientific Evidence for HMB?

According to many but not all of the small double-blind trials performed thus far, HMB may improve response to weight training.^40–46 HMB might help prevent muscle damage during prolonged exercise.⁴⁷

Muscle Building Studies on chick and rat muscles suggest that HMB reduces the amount of muscle protein that breaks down during exercise.⁴⁸

In a controlled study, 41 male volunteers aged 19 to 29 were given either 0, 1.5, or 3 g of HMB daily for 3 weeks.⁴⁹ The participants also lifted weights 3 days a week for 90 minutes. The results suggested that HMB can enhance strength and muscle mass in direct proportion to intake.

In another controlled study reported in the same article, 32 male volunteers took either 3 g of HMB daily or placebo, and then lifted weights for 2 or 3 hours daily, 6 days a week for 7 weeks. The HMB group saw a significantly greater increase in its bench-press strength than the placebo group. However, there was no significant difference in body weight or fat mass by the end of the study.

Another double-blind placebo-controlled trial of 39 men and 36 women found that over 4 weeks HMB supplementation improved response to weight training.⁵⁰

Two placebo-controlled studies in women found that 3 g of HMB had no effect on lean body mass and strength in sedentary women, but it did provide an additional benefit when combined with weight training.⁵¹ In addition, a double-blind study of 31 men and women, 70 years old, undergoing resistance training found significant improvements in fat-free mass attributable to the use of HMB (3 g daily).⁵² 

However, other studies have found marginal or no benefits with HMB for enhancing body composition or strength. ^53,54,233 HMB may have greater effects on lean body mass and muscle strength when combined with creatine.^53,224

All of these studies were small, and therefore, their results are not reliable. Larger studies will be necessary to truly establish whether HMB is helpful for power athletes working to enhance strength and muscle mass.

For more information, including dosage and safety issues, see the full HMB article.

Vitamin C: May Aid Recovery by Preventing the "Post-Marathon Sniffle"

While being active in sports can improve your physical (and mental) well-being, it also places higher stresses on your body, and can end up damaging your system. Preventative maintenance to the rescue! In addition to eating right and getting enough sleep, taking vitamin C may help as well.

Apart from providing some of our basic nutritional needs, this vitamin's greatest benefit to athletes is its potential for preventing colds.^58,59,60 Extremely intense exercise, such as training for and running in a marathon, is known to lower immunity, and endurance athletes frequently get sick after maximal exertion. When we exercise at a highly competitive level or train intensely for a competitive athletic event, we stress our bodies as we push them to perform, and sickness may be the result. Vitamin C might help prevent this, although not all studies agree. (See also Glutamine in Supplements for Recovery, below.)

As an additional bonus, vitamin C may also help reduce muscle soreness due to exertion.⁶¹

What Is the Scientific Evidence for Vitamin C?

According to a double-blind placebo-controlled study involving 92 runners, taking 600 mg of vitamin C for 21 days prior to a race made a significant difference in the incidence of sickness afterwards.⁶² Within 2 weeks after the race, 68% of the runners taking placebo developed cold symptoms, versus only 33% of those taking the vitamin C supplement. As part of the same study, non-runners of similar age and gender to those running were also given vitamin C or placebo. Interestingly, for this group, the supplement had no apparent effect on the incidence of upper respiratory infections. Vitamin C seemed to be specifically effective in this capacity for those who exercised intensively.

Two other studies found that vitamin C could reduce the number of colds experienced by groups of people involved in rigorous exercise in extremely cold environments.⁶³ One study involved 139 children attending a skiing camp in the Swiss Alps, while the other enrolled 56 military men engaged in a training exercise in Northern Canada during the winter months. In both cases, the participants took either 1 g of vitamin C or placebo daily at the time their training program began. Cold symptoms were monitored for 1 to 2 weeks following training, and significant differences in favor of vitamin C were found.

However, one very large study of 674 marine recruits in basic training found no such benefit.⁶⁴ The results showed no difference in the number of colds between the treatment and placebo groups.

What's the explanation for this discrepancy? There are many possibilities. Perhaps basic training in the marines is significantly different from the other forms of exercise studied. Another point to consider is that the marines didn't start taking vitamin C right at the beginning of training, but waited 3 weeks. The study also lasted a bit longer than the positive studies mentioned above, continuing for 2 months; maybe vitamin C is more effective at preventing colds in the short term. Of course, another possibility is that it doesn't really work. More research is needed to know for sure.

One double-blind trial compared vitamin C, vitamin E, and placebo for muscle soreness in 24 male volunteers.⁶⁵ Vitamin C was found to relieve muscle soreness, while vitamin E did not. However, larger trials are needed to resolve whether or not vitamin C is effective in preventing muscle soreness.

For more information, including dosage and safety issues, see the full vitamin C article.

Nutrition and Training: Good for All Athletes

We may be stating the obvious, but supplements alone will not improve your strength or endurance in the absence of a good training program and a healthy diet. Increased muscle mass or stamina is the result of an appropriate exercise program supported by adequate intake of calories and essential nutrients, including fuel for energy, protein, fluids, vitamins, and minerals.

Just like your car requires more gasoline if you drive farther, your body requires more fuel if you exercise more. In addition to carbohydrates and fats which provide fuel during a workout, you need adequate protein to prevent the muscles that you're working so hard to build up from breaking down. One researcher's recommendation for protein intake is 1.2 to 1.4 g of protein per kilogram of body weight (1 kilogram equals about 2.2 pounds) if you pursue endurance-type sports, such as marathon running.⁷⁵ If you are involved in strength-building sports such as weight lifting, 1.4 to 1.8 g per kilogram body weight is suggested. These amounts are higher than the current recommended daily intakes for protein, which may be more appropriate for people with a less active lifestyle. Protein supplements such as soy or whey powders, or protein hydrosylates, are sometimes used to boost protein intake. However, taking protein in the form of separate amino acids does not appear to offer any additional benefit (see Amino Acids in Ergonomic Aids, below).

Whether adding vitamins and minerals over and above the amount suggested by the recommended daily intake is necessary or beneficial to athletes is an unresolved issue. Several vitamins and minerals are used as sports supplements, and we'll discuss them in the sections below.

Sports Beverages

Sports beverages may also be beneficial. Most obviously, they provide fluids, helping to avoid exercise-induced dehydration. In addition, they contain varying amounts of carbohydrates and electrolytes. These carbohydrates can be important because once your body has burned up all the fuel that was available in your bloodstream, it will begin to use the glycogen stored in your muscles, which can cause muscle wasting. Consuming carbohydrates has been found to prevent loss of muscle tissue during intense exercise, to delay fatigue, and even to improve performance times in some cases.⁷⁶

The electrolytes in most sports drinks help to prevent dehydration and other potential problems related to electrolyte imbalances. Major electrolytes in your body include potassium, sodium, and chloride, with potassium and sodium working together like a molecular seesaw: when the level of one goes up, the other goes down. All together, these three dissolved minerals play an essential chemical role in every function of your body. Making sure you have enough of them will enhance your performance and improve your recovery.

Other Proposed Treatments for Sports Performance

Numerous other supplements are commonly recommended for athletes. Unfortunately, the evidence that they work is marginal at best.

Some supplements are marketed as ergogenic aids, said to improve speed, strength, or endurance.

These include medium-chain triglycerides (MCTs), ginseng, branched-chain amino acids (BCAAs), stimulants (ephedrine and caffeine), pyruvate (DHAP), nicotinamide adenine dinucleotide (NADH), B vitamins, coenzyme Q₁₀, carnitine, inosine, ribose, trimethylglycine (TMG), suma, phosphate, policosanol, schisandra, certain minerals (copper, magnesium, iron, and zinc), and a Chinese medicine called cordyceps. Certain commercial preparations that combine herbs and supplements are also marketed as ergogenic aids.

Supplements reputed to increase muscle mass or improve muscle/fat ratio include phosphatidylserine (PS), pyruvate, BCAAs, conjugated linoleic acid, lipoic acid, ipriflavone, gamma oryzanol, the herb Tribulus terrestris, and chromium.

Some sports supplements aren't aimed at improving performance directly but are instead intended to speed recovery time, whether by helping injuries to heal more quickly or restoring the body's natural balance after the stress of exertion. Like vitamin C, glutamine may help prevent colds following intense exercise. Various antioxidants may reduce muscle soreness. Other supplements are said to help prevent or treat athletic injuries, including glucosamine, oligomeric proanthocyanidins (OPCs), bromelain, other proteolytic enzymes, and horse chestnut.

In the following sections, we'll discuss many of these substances briefly, describing the level of evidence behind them.

Other Proposed Ergogenic Aids

Many substances besides those mentioned earlier are marketed as ergogenic aids, but there is little to no evidence that they work.

Medium-Chain Triglycerides (MCTs)

Medium-chain triglycerides (MCTs) are fats with an unusual chemical structure that allows the body to digest them easily. Most fats are broken down in the intestine and remade into a special form that can be transported in the blood. But MCTs are absorbed intact and taken to the liver, where they are used directly for energy. In this sense, they are processed very similarly to carbohydrates. For that reason, MCTs have been proposed as an alternative to "carbo-loading" for providing a concentrated source of easily utilized energy.

A number of double-blind trials using MCTs for improving high-intensity or endurance exercise performance have been conducted, but the results have been thoroughly inconsistent.^{77–80,225,226} This is not surprising, as none of these studies enrolled enough participants to provide trustworthy results.

Phosphatidylserine

Phosphatidylserine (PS) is a phospholipid and a major component of cell membranes. Good evidence suggests that PS can improve mental function, especially in the elderly.^81–93

Recently, PS has also been marketed as a sports supplement, said to help bodybuilders and power athletes develop larger and stronger muscles. This is based on modest evidence that PS slows the release of cortisol following heavy exercise.^94,95,96 Cortisol is a hormone that causes muscle tissue to break down. For reasons that are unclear, the body produces increased levels of cortisol after heavy exercise. Strength athletes who believe natural cortisol release works against their efforts to rapidly build muscle mass hope that PS will help them advance more quickly. However, there is no direct evidence yet to support claims that PS actually helps to build muscles more quickly and with less training effort.

Ginseng

There are actually three different herbs commonly called ginseng: Asian or Korean ginseng (Panax ginseng), American ginseng (Panax quinquefolius), and Siberian "ginseng" (Eleutherococcus senticosus). The latter is actually not ginseng at all, but the Russian scientists responsible for promoting it believe that it functions identically. According to some experts, another herb, ciwujia, is actually Eleutherococcus, while others claim it is a related but different species.

The evidence for Panax ginseng as a sports supplement is mixed. An 8-week double-blind placebo-controlled trial evaluated the effects of Panax ginseng with and without exercise in 41 individuals.⁹⁷ The participants were given either ginseng or placebo, and then underwent exercise training or remained untrained throughout the study. The results showed that ginseng improved aerobic capacity in individuals who did not exercise, but offered no benefit in those who did exercise. In a 9-week double-blind placebo-controlled trial of 30 highly trained athletes, treatment with Panax ginseng or Panax ginseng plus vitamin E produced significant improvements in aerobic capacity.⁹⁸ Another double-blind placebo-controlled trial of 37 individuals also found some benefit.⁹⁹ A double-blind placebo-controlled study of 120 individuals found that ginseng gradually improved reaction time and lung function over a 12-week treatment period among those 40 to 60 years old.¹⁰⁰ No benefits were seen in younger individuals.

However, no benefit could be demonstrated with Panax ginseng in an 8-week, double-blind trial that followed 31 healthy men in their twenties.¹⁰¹ Many other small trials of Panax ginseng have failed to find evidence of benefit.^{102–107, 232,238}

A double-blind study of 20 endurance athletes over an 8-week period failed to find evidence of benefit with a standard Eleutherococcus formulation.¹⁰⁸ Lack of benefit was also seen in another small double-blind crossover trial.¹⁰⁹ Furthermore, in a small double-blind, placebo-controlled trial of endurance athletes, use of eleutherococcus actually increased physiological signs of stress during intensive training.²³⁸

Branched-Chain Amino Acids (BCAAs): Leucine, Isoleucine, and Valine

Amino acids are molecules that form proteins when joined together. Three of them—leucine, isoleucine, and valine—are called branched-chain amino acids (BCAAs), describing the shape of the molecules. Muscles have a particularly high BCAA content.

Both strength training and endurance exercise use up greater amounts of BCAAs than normal daily activities,¹¹⁰ perhaps increasing an athlete's need for dietary intake of these amino acids. Sports such as mountaineering and skiing may cause even greater depletion of BCAAs because of metabolic changes that occur at higher altitudes. Athletes have tried BCAA supplements to build muscle, improve performance, postpone fatigue, and cure "overtraining syndrome" (see Supplements for Recovery below); however, most of the evidence suggests that they do not work.^111–118

Conjugated Linoleic Acid (CLA)

Conjugated linoleic acid (CLA) is a mixture of different isomers, or chemical forms, of linoleic acid. Although linoleic acid itself is an essential fatty acid—a type of fat that your body needs as much as it needs vitamins—there is no evidence that you need CLA in your diet. If you choose to include it, supplements are the only practical source.

The evidence that CLA can help you lose fat while retaining muscle remains highly preliminary.^{119–122,232}

Amino Acids

Athletes use a number of amino acids as supplements for a variety of purposes, sometimes individually and sometimes in combination. Amino acids are sometimes taken as protein supplements, as they are the components from which proteins are formed. Some individual amino acids are also biochemically active, and taking them alone might alter your metabolism or change your hormone balance. However, evidence supporting the use of amino acids as ergogenic aids is sparse to nonexistent. The few clinical trials performed generally don't show positive results,^123,124 and there is no evidence that amino acids are better than whole protein.

Those amino acids believed by some to be ergogenic include arginine, glutamine, and ornithine (ornithine and glutamine combined form ornithine alpha-ketoglutarate, OKG), as well as the branched-chain amino acids leucine, isoleucine, and valine, discussed above. Glutamine is also used for overtraining syndrome (see Supplements for Recovery below).

Stimulants: Ma Huang (Ephedra), Caffeine (Coffee, Tea, Guarana, Cola, etc.)

A number of plant-derived stimulants are used by some athletes to improve their performance, including ephedrine from the Chinese herb ma huang (also called ephedra) and caffeine from coffee, tea, cola, or guarana (a plant native to South America). Both ephedrine and caffeine are central nervous system stimulants. Caffeine also appears to change the way your body burns calories, possibly allowing it to burn fats first and preserve muscle glycogen for later on in the competition—sort of like "saving the best for last."¹²⁵

Ephedrine's value in enhancing sports performance has not been established; at the same time, there are serious safety issues associated with its use (see Safety Issues in the full article on ephedra). Some sports federations have determined that specific amounts of ephedrine in an athlete's system are grounds for disqualification.

Caffeine does appear to improve performance during endurance-type exercises.¹²⁶Note: The International Olympic Committee has set a tolerance limit for caffeine in the urine at 12 mcg/ml. If you're competing in a sport that follows similar regulations, you may want to have a cup of coffee or tea, but don't drink the whole pot.

Pyruvate (Dihydroxyacetone Pyruvate, DHAP)

Pyruvate supplies the body with pyruvic acid, a natural compound that plays important roles in the manufacture and use of energy. Pyruvate supplements have become popular with bodybuilders and other athletes based on slim evidence that pyruvate can improve body composition.^127–130 However, at the present time, the evidence regarding pyruvate as an ergogenic aid is weak and contradictory.^131–134

Nicotinamide Adenine Dinucleotide (NADH)

Short for nicotinamide adenine dinucleotide, NADH is an important cofactor ("assistant") that helps enzymes in their work throughout the body. NADH particularly plays a role in producing energy (ATP or adenosine triphosphate, your body's preferred fuel). It's possible that taking supplemental NADH could help speed up ATP synthesis. However, NADH has to undergo some chemical changes to participate in ATP formation, and we don't really know if supplemental NADH gets processed in a way that allows it to be effective. NADH is one of those supplements that appeared on the market before it was sufficiently evaluated. Its use is completely speculative at present.

B-Complex Vitamins

The recommended daily intakes for B vitamins are based on caloric intake. Because people who are exercising rigorously on a regular basis are likely to consume more calories than the average person, supplementation with B vitamins may thus be appropriate. Vitamin B₂ (also called riboflavin) and vitamin B₅ (pantothenic acid) have also been proposed as performance enhancers for athletes, but there is no real evidence that either is effective for this.

Lipoic Acid

Lipoic acid is now being used by some athletes as an "insulin mimicker" because it appears to increase the body's utilization of blood sugar,^135,136 which in turn might help build muscle glycogen. However, no studies have yet been done to determine whether or not lipoic acid supplementation actually increases muscle glycogen, so this use is purely theoretical at present.

Coenzyme Q₁₀ (CoQ₁₀, or Ubiquinone)

Coenzyme Q₁₀ (CoQ₁₀), also known as ubiquinone, is an antioxidant discovered by researchers at the University of Wisconsin in 1957. Its name comes from the word ubiquitous, meaning "found everywhere." Indeed, CoQ₁₀ is found in every cell in the body, where it plays a fundamental role in the mitochondria, the parts of the cell that produce energy from food. Its best-established use is for congestive heart failure. CoQ₁₀ has also been used as a performance enhancer for athletes, but most clinical trials have found no significant improvement with CoQ₁₀, and one group reported significant worsening of performance with the supplement compared to placebo.^137–143

Coenzyme Q₁₀ might be of some value as a recovery supplement because of its antioxidant properties (see Supplements for Recovery, below).

Carnitine

Carnitine is a compound the body uses to turn fat into energy. It is not considered an essential nutrient, because the body can manufacture all it needs. However, supplemental carnitine may improve the ability of certain tissues to produce energy. Principal dietary sources of carnitine are meat and dairy products, but a supplement is necessary to obtain therapeutic dosages. Carnitine is widely touted as a physical performance enhancer, but there is no real evidence that it is effective, and some research indicates that it does not work in this capacity.¹⁴⁴

Inosine

Inosine is an important chemical found throughout the body. It plays many roles, one of which is helping to make ATP, the body's main form of usable energy. Based primarily on this fact, inosine supplements have been proposed as an energy booster for athletes. However, most of the available evidence suggests that it doesn't work for this purpose.^145–149

Ipriflavone

Ipriflavone is a semisynthetic version of an isoflavone (water-soluble chemicals found in many plants) from soy. Ipriflavone is also touted as a bodybuilding aid, but no real evidence supports this use.

Ribose

Ribose is a carbohydrate also vital for the manufacture of ATP. Ribose has been tried for improving exercise capacity in individuals with certain enzyme deficiencies and other rare conditions that cause muscle pain during exertion. There is weak evidence that it may help people with some of these conditions—but not others—to exercise without pain.^150,151

Ribose has recently been touted as an important new athletic performance enhancer; however, there is as yet no evidence at all that it works. Although at least one animal study seems to show that skeletal muscle replenishes ATP ("ready to go" chemical energy for your cells) more quickly when ribose is added to the blood,¹⁵² the one reported double-blind trial in humans found neither enhanced sports performance nor improved ATP resynthesis.²²⁷

Gamma Oryzanol

Very preliminary evidence suggests that gamma oryzanol, which is derived from rice bran oil, may increase endorphin release and aid muscle development.^153,154 These findings have created interest in using gamma oryzanol as a sports supplement. However, a 9-week, double-blind, placebo-controlled trial of 22 weight-trained males found no difference between placebo or 500 mg daily of gamma oryzanol in terms of performance, body composition, or hormone levels.¹⁵⁵

Trimethylglycine (TMG)

Trimethylglycine (TMG) is a naturally occurring compound that may help to prevent atherosclerosis and is therefore sometimes taken as a supplement. In the course of doing its work to keep your blood vessels clear, TMG is turned into another substance, dimethylglycine (DMG).

In Russia, DMG is used extensively as an athletic performance enhancer and has recently become popular among American athletes. TMG is cheaper, and may have the same effects as DMG, as it changes into DMG in the body. However, one small study suggests that DMG does not work,¹⁵⁶ making the use of TMG as a sports supplement seem rather pointless.

Suma

Suma is a large ground vine native to Central and South America. Sometimes called "Brazilian ginseng," native people have long used suma to promote robust health as well as to treat practically all illnesses. They called it Para Toda, which means "for all things."¹⁵⁷

Russian Olympic athletes have used suma, along with other adaptogens, in the belief that it will enhance sports performance. In the United States, suma is sometimes recommended as a general body strengthener. However, there has been little formal scientific investigation of suma at this time.

Tribulus terrestris

Tribulus terrestris is a tropical plant with a long history of medicinal use. It has been tried for low libido in both men and women, female infertility, and impotence. In addition, it has been studied as a treatment for heart disease.¹⁵⁸

One theory regarding how T. terrestris might help with sexual problems is that a component from the plant called protodioscine is converted to the hormone DHEA in our bodies.¹⁵⁹ DHEA is used by the body as a building block for both testosterone and estrogen (as well as other hormones).

This finding has led bodybuilders and strength athletes to try T. terrestris for increasing muscular development. So far, however, the scientific evidence seems to be against it; this is not surprising, as DHEA itself has not been found effective as a sports supplement.

One study involving 15 men compared the effects of T. terrestris (3.21 mg per kilogram of body weight—292 mg daily for a 200-lb man) against placebo on body composition and endurance among men engaged in resistance training.¹⁶⁰ At the end of the 8-week study, the only significant difference between the treatment and placebo groups was that the placebo group showed greater gains in endurance.

For more information, including dosage and safety issues, see the full Tribulus terrestris article.

Phosphate

Phosphate has been studied as an ergogenic aid to improve aerobic capacity and endurance with greatly mixed results.^164,165 One unanswered question is whether the findings in some studies resulted from the ingestion of phosphate or from the other compounds the phosphate was mixed with, such as sodium or calcium. Because the trials performed so far have used inconsistent methods and measurements, it isn't possible to know yet whether or not phosphate has any potential benefit as a sports supplement.

Policosanol

Policosanol is a mixture of waxy substances manufactured from sugarcane. It contains octacosanol, which is also made from wheat germ oil. Both are marketed as performance-enhancing dietary supplements. They are said to increase muscle strength and endurance and improve reaction time and stamina, but there is no reliable scientific evidence as yet to support these claims.

The only evidence for policosanol as a performance enhancer comes from one small double-blind trial with marginal results.¹⁶⁶

Glutamine

Two small, double-blind, placebo-controlled trials failed to find the amino acid glutamine effective for improving response to resistance training (weight lifting).^235,237

Mineral Supplements

Chromium, magnesium, iron, zinc, and copper have all been marketed as having potential to aid athletes in achieving their goals. However, there is little evidence that taking these minerals will prove helpful if you are not deficient.^167,168 Deficiencies in magnesium, zinc, and chromium are probably most likely.

Chromium has been sold as a "fat burner" and is also said to help build muscle tissue. While studies evaluating its effects on weight loss are contradictory, the largest study suggests that it might offer some benefit.^169–174 However, studies evaluating its benefits as a performance enhancer or aid to bodybuilding have yielded almost entirely negative results.^{175–183,236} 

Studies on magnesium supplements have returned contradictory results.^184–191  

The majority of athletes are probably not iron deficient, and you shouldn't take iron supplements if you already have enough iron in your body. However, if you are deficient in this essential mineral, iron supplements may help. A double-blind placebo-controlled trial of 42 non-anemic women with evidence of slightly low iron reserves found that iron supplements significantly increased the benefits gained from exercise.¹⁹² Participants were put on a daily aerobic training program for the latter 4 weeks of this 6-week trial. At the end of the trial, those receiving iron showed significantly greater gains in speed and endurance as compared to those given placebo.

In addition, a double-blind placebo-controlled study of 40 non-anemic elite athletes with mildly low iron stores found that 12 weeks of iron supplementation enhanced aerobic performance.¹⁹³

There is no real evidence that zinc or copper will improve sports performance. While zinc deficiency is relatively common, taking too much zinc can be harmful.

For more information on dosage and safety, see the individual articles on copper, chromium, iron, magnesium, and zinc.

Cordyceps

Cordyceps is a traditional Chinese medicinal substance, part fungus, part caterpillar. Its use as a sports supplement is based entirely on the belief that it combats the effects of aging, but there is no scientific evidence to support this idea.

Commercial Preparations

We don't have scientific evidence on every formula touted for improving sports performance. However, one small double-blind study of a mixture of various herbs and supplements marketed as SPORT® found no evidence that it can improve sports performance in trained athletes.¹⁹⁴

Other Supplements for Recovery

The stresses of sports competitions can sometimes weaken you, and injuries can keep an athlete out of training and impede performance. The less "down-time," the better. The substances discussed in this section have been proposed for sustaining health or speeding recovery, but none have been proven effective at this time.

Preventing Infections

Earlier in this article, we discussed the evidence that vitamin C might help prevent the infections that can follow intense exercise. The amino acid glutamine may be helpful for this purpose as well. This idea is based on findings that the amount of glutamine in the blood system of an athlete who has trained very hard is lower than the norm.¹⁹⁵ Glutamine is an important fuel source for some of our immune system cells, and it is possible that the drop in glutamine is associated with the high incidence of infections that occur in athletes who have overtrained, although not all studies agree.^{196–199,231}

One double-blind clinical trial involving 151 athletes found that supplementation with 5 g of glutamine immediately after heavy exercise, followed by another 5 g 2 hours later, reduced the incidence of infections quite significantly.²⁰⁰ Only 19% of those taking glutamine reported infections, while 51% of the placebo group succumbed to illness. For more information, including dosage and safety issues, see the full glutamine article.

Thymus extract is a supplement derived from the thymus gland of cows and is thought to enhance immune function. However, a double-blind placebo-controlled trial of 60 athletes failed to find any significant evidence of benefit with thymus extract.²⁰¹ In addition, there are significant safety issues with thymus extract (see the full article for details).

Traumatic Injuries

Bruises and sprains are common among athletes. There is some evidence that various supplements may enhance recovery from these injuries. The most popular are bromelain, other proteolytic enzymes,^202–205 oligomeric proanthocyanidin complexes (OPCs), and/or horse chestnut, although the evidence isn't strong. See the full articles on each of these topics for more information.

In addition, creatine might be helpful for reducing the muscle weakness that develops when a limb is immobilized following injury.^228,229

Some athletes also use glucosamine (best known for its use in treating osteoarthritis) in the unproven belief that it can help prevent muscle injuries, relieve tendinitis, and repair damaged cartilage. However, there is no scientific evidence to support these ideas yet.

Muscle Soreness

Muscle soreness is a common problem among hard-training athletes. A treatment that could reduce such soreness might help an athlete train harder.

As mentioned previously, exercising increases the presence of free radicals, naturally occurring substances that can damage tissue. Some researchers have theorized that such damage may in part cause the muscle soreness, and perhaps muscle deterioration, that can accompany a strenuous workout.^206,207 Based on this theory, various antioxidants have been proposed to help prevent athletic muscle soreness, including selenium, beta-carotene, vitamin C, vitamin E, OPCs, and coenzyme Q_10. 

Vitamin E has also been suggested as a treatment to prevent symptoms that can occur after endurance running, such as gastrointestinal bleeding, stomach cramps, nausea, or muscle injury; however, one double-blind trial found no significant benefit for any of these symptoms.²⁰⁸

The supplement phosphatidylserine (PS) might also help treat muscle soreness due to its effects on cortisol. (See Phosphatidylserine in Ergogenic Aids, above, for details.)

Not Recommended Treatments

At least four commonly recommended supplements fall in the "not recommended" category.

Hormones

Although they are often sold as supplements, androstenedione and dehydroepiandrosterone (DHEA) are really hormones. The long-term consequences of using these "supplements" are unknown. They alter your body's hormone balance, which may cause unpredictable side effects. For this reason, we do not recommend the use of these substances. In addition, there is no real evidence that they work.

Androstenedione is sometimes used by athletes based on the belief that it will increase the amount of testosterone in the system. However, double-blind studies of androstenedione have found that it does not alter total testosterone levels, or improve sports performance, strength, or lean body mass.^209–214 The most consistent effect of androstenedione is to increase estrogen levels in the body.

Athletes have used DHEA on the belief that (like phosphatidylserine) it might limit the body's response to cortisol and thereby cause an increase in muscle tissue growth. However, study results have been mixed, so it's uncertain whether DHEA really interferes with cortisol or not.^215,216 In any case, most (but not all), studies have found no performance benefits from taking DHEA.^217,218,219

Minerals

The mineral vanadium has been suggested for use by bodybuilders based on its effects on insulin, but there is no evidence that it works. A double-blind placebo-controlled study involving 31 weight-trained athletes found no benefit of supplementation at more than 1,000 times the nutritional dose.²²⁰ Furthermore, there are serious safety concerns about taking vanadium at such high doses (see full article on vanadium).

The mineral boron has also been proposed as a sports supplement based on its potential to alter the body's hormone balance. However, clinical studies suggest that boron supplementation is more likely to increase your estrogen levels than help you produce more testosterone.^221,222,223 Elevated estrogen levels have been associated with increased rates of some types of cancer, so we don't recommend taking supplemental boron. Far more research needs to be done on boron before it should be considered either safe or effective.

Last reviewed June 2002 by Medical Review Board

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