During the early stages of endurance exercise, caffeine might mobilize free fatty acids as a source of energy and spare muscle glycogen [ 38 ]. Caffeine is commonly used in energy drinks and shots touted for their performance-enhancement effects [ 87 , 88 ]. It is also found in energy gels containing carbohydrates and electrolytes as well as in anhydrous caffeine-only pills.

For an individual weighing pounds 70 kg , this dose is equivalent to — mg caffeine. Taking more, however, is unlikely to improve performance further and increases the risk of side effects. A review of the literature found that caffeine intake affected sport-specific performance e.

Although 30 of the 33 trials showed positive improvements in performance, the improvements were not statistically significant in half of them [ 85 ].

In these studies, performance improvement ranged from a decrease of 0. Factors such as the timing of ingestion, caffeine intake mode or form, and habituation to caffeine could also have accounted for the varied effects on performance.

Caffeine supplementation is more likely to help with endurance-type activities such as running and activities of long duration with intermittent activity such as soccer than more anaerobic, short-term bouts of intense exercise such as sprinting or lifting weights [ 91 ]. Some evidence suggests that caffeine is more likely to improve performance in people who are not habituated to it [ 85 ].

However, other evidence shows no habituation effect of caffeine consumption on performance [ 92 ]. Other adverse effects of caffeine include insomnia, restlessness, nausea, vomiting, tachycardia, and arrhythmia [ ].

Caffeine does not induce diuresis or increase sweat loss during exercise and therefore does not reduce fluid balance in the body that would adversely affect performance [ 13 , 90 , 98 ]. For healthy adults, the U. The American Academy of Pediatrics warns that caffeine-containing energy drinks in particular have no place in the diets of children or adolescents and are not suitable for use during routine physical activity [ ].

Pure powdered caffeine is available as a dietary supplement and is very potent. Furthermore, combining caffeine with other stimulants could increase the potential for adverse effects [ 94 ].

At least two young men have died as a result of taking an unknown amount of pure powdered caffeine [ ]. Caffeine is easily and rapidly absorbed, even from the buccal membranes in the mouth, and is distributed throughout the body and brain. It reaches peak concentrations in the blood within 45 minutes of consumption and has a half-life of about 4—5 hours [ 83 ].

For a potential benefit to athletic performance, users should consume caffeine 15 to 60 minutes before exercise [ 13 , 85 ]. Consumption of caffeine with fluid during exercise of long duration might extend any performance improvements [ 85 ]. In a position statement, the AND, DoC, and ACSM state that caffeine supplementation reduces perceived fatigue and enables users to sustain exercise at the desired intensity longer [ 12 ].

The U. It adds that caffeine could reduce perceived exertion when exercise lasts longer. The Australian Institute of Sport supports the use of caffeine for improving sports performance in suitable athletic competitions under the direction of an expert in sports medicine, but it notes that more research might be required to understand how caffeine should be used for best results [ 29 ].

The World Anti-Doping Agency does not prohibit or limit caffeine use [ ]. L-citrulline is a nonessential amino acid produced in the body, mainly from glutamine, and obtained from the diet. Watermelon is the best-known source; 1 cup diced seedless watermelon has about mg citrulline [ ].

The subsequent conversion of arginine to nitric oxide, a potent dilator of blood vessels, might be the mechanism by which citrulline could serve as an ergogenic aid. In fact, consumption of citrulline might be a more efficient way to raise blood arginine levels than consumption of arginine because more citrulline is absorbed from the gut than arginine.

Most studies have used citrulline malate, a combination of citrulline with malic acid a constituent in many fruits that is also produced endogenously , because malate, an intermediate in the Krebs cycle, might enhance energy production [ 30 ].

The research to support supplemental citrulline as an ergogenic aid is limited and conflicting at best. The few published studies have had heterogeneous designs and ranged in duration from 1 to 16 days.

As an example, in one randomized controlled study with a crossover design, 41 healthy male weightlifters age 22—37 years consumed 8 g citrulline malate or a placebo 1 hour before completing barbell bench presses to exhaustion [ ].

Overall, participants could complete significantly more repetitions when taking the supplement and reported significantly less muscle soreness 1 and 2 days after the test.

Another study that randomized 17 young healthy men and women to take citrulline without malate either 3 g before testing or 9 g over 24 hours or a placebo found that participants using the citrulline did not perform as well as those taking the placebo on an incremental treadmill test to exhaustion [ ].

Although citrulline supplementation might increase plasma levels of nitric oxide metabolites, such a response has not been directly related to any improvement in athletic performance [ 30 ]. Studies have not adequately assessed the safety of citrulline, particularly when users take it in supplemental form for months at a time.

In the study of weight lifters described above, 6 of the 41 participants reported stomach discomfort after taking the supplement [ ].

The research to date does not provide strong support for taking citrulline or citrulline malate to enhance exercise or athletic performance [ 30 ]. Whether athletes in specific sports or activities might benefit from taking supplemental citrulline remains to be determined [ ].

Dietary supplements that contain citrulline provide either citrulline or citrulline malate. Citrulline malate is Sellers of some citrulline malate dietary supplements claim that they provide a higher percentage of citrulline with labels listing, for example, citrulline malate or tri-citrulline malate , but studies have not determined whether these supplements are superior to standard citrulline or citrulline malate supplements.

Creatine is one of the most thoroughly studied and widely used dietary supplements to enhance exercise and sports performance [ ]. Creatine is produced endogenously and obtained from the diet in small amounts. It helps generate ATP and thereby supplies the muscles with energy, particularly for short-term events [ ].

A person weighing pounds has about g creatine and phosphocreatine in his or her body, almost all in the skeletal and cardiac muscles [ ]. However, it is only when users consume much greater amounts of creatine over time as a dietary supplement that it could have ergogenic effects.

Metabolized creatine is converted into the waste product creatinine, which is eliminated from the body through the kidneys. Studies in both laboratory and sports settings have found that short-term creatine supplementation for 5 to 7 days in both men and women often significantly increases strength e.

In one example, a study randomized 14 healthy, resistance-trained men age 19—29 years to receive 25 g creatine monohydrate or a placebo for 6—7 days [ ]. Participants taking the supplement had significant improvements in peak power output during all five sets of jump squats and in repetitions during all five sets of bench presses on three occasions.

Compared with those taking the placebo, participants taking the creatine improved their performance in both meter sprints and six intermittent m sprints. Supplementation with creatine over weeks or months helps training adaptations to structured, increased workloads over time.

Individuals have varied responses to creatine supplementation, based on factors such as diet and the relative percentages of various muscle fiber types [ , ].

Vegetarians, for example, with their lower muscle creatine content, might have greater responses to supplementation than meat eaters. Overall, creatine enhances performance during repeated short bursts of high-intensity, intermittent activity, such as sprinting and weight lifting, where energy for this predominantly anaerobic exercise comes mainly from the ATP-creatine phosphate energy system [ 38 , ].

Creatine supplementation seems to be of little value for endurance sports, such as distance running or swimming, that do not depend on the short-term ATP-creatine phosphate system to provide short-term energy, and it leads to weight gain that might impede performance in such sports [ , ].

Furthermore, in predominantly aerobic exercise lasting more than seconds, the body relies on oxidative phosphorylation as the primary energy source, a metabolic pathway that does not require creatine [ ].

Studies have found no consistent set of side effects from creatine use, except that it often leads to weight gain, because it increases water retention and possibly stimulates muscle protein synthesis [ , ].

Several studies have found that supplemental creatine monohydrate, when used for a strength-training program, can lead to a 1—2 kg increase in total body weight in a month [ 73 ]. Creatine is considered safe for short-term use by healthy adults [ 12 , , , ].

In addition, evidence shows that use of the product for several years is safe [ , ]. Anecdotal reactions to creatine use include nausea, diarrhea and related gastrointestinal distress, muscle cramps, and heat intolerance.

Creatine supplementation may reduce the range of motion of various parts of the body such as the shoulders, ankles, and lower legs and lead to muscle stiffness and resistance to stretching [ ]. Adequate hydration while taking creatine might minimize these uncommon risks [ ].

In a position statement, the AND, DoC, and ACSM advise that creatine enhances performance of cycles of high-intensity exercise followed by short recovery periods and improves training capacity [ 12 ].

In its position statement, the ISSN states that creatine monohydrate is the most effective nutritional supplement currently available for enhancing capacity for high-intensity exercise and lean body mass during exercise [ ].

The ISSN contends that athletes who supplement with creatine have a lower incidence of injuries and exercise-related side effects compared to those who do not take creatine [ ]. The Australian Institute of Sport supports the use of creatine for improving sports performance in suitable athletic competitions under the direction of an expert in sports medicine, but it notes that more research might be required to understand how the supplement should be used for best results [ 29 ].

In some studies, the loading dose is based on body weight e. Other, usually more expensive, forms of creatine e. Deer antler velvet consists of cartilage and epidermis from growing deer or elk antlers before ossification [ , ].

It is used as a general health aid in traditional Chinese medicine. Several growth factors have been detected in deer antler velvet, such as IGF-1, that could promote muscle tissue growth in a similar way to the quick growth of deer antlers.

Three randomized controlled trials in a total of 95 young and middle-age men and 21 young females provide virtually no evidence that deer antler velvet supplements improve aerobic or anaerobic performance, muscular strength, or endurance [ , ].

The supplements provided no significant ergogenic effects compared with placebo. Studies have not adequately assessed the safety of deer antler velvet. The studies cited above found no side effects in participants taking deer-antler-velvet supplements.

IGF-1 is available as a prescription medication, and its reported side effects include hypoglycemia, headache, edema, and joint pain [ ]. An evaluation of six deer-antler-velvet dietary supplements that were commercially available in found that five of them contained no deer IGF-1, and four were adulterated with human IGF-1 [ ].

Only one of the six supplements contained a low level of deer IGF The research to date does not support taking deer-antler-velvet supplements to enhance exercise or athletic performance. The National Collegiate Athletic Association [ ] and the World Anti-Doping Agency [ ] ban the use of IGF-1 and its analogues in athletic competition.

DHEA is a steroid hormone secreted by the adrenal cortex. The body can convert DHEA to the male hormone testosterone; testosterone's intermediary, androstenedione; and the female hormone estradiol [ ]. Testosterone is an anabolic steroid that promotes gains in muscle mass and strength when combined with resistance training [ ].

The minimal research on DHEA's use to enhance exercise and athletic performance provides no evidence of benefit [ ]. Compared to placebo, the DHEA and androstenedione produced no statistically significant increase in strength, aerobic capacity, lean body mass, or testosterone levels [ ].

The supplement provided no benefits compared with placebo in increasing muscle strength, lean body mass, or testosterone concentrations [ ]. Studies have not adequately assessed the safety of DHEA.

The two short-term studies in men described above found no side effects from the DHEA; blood lipid levels and liver function remained normal. Other studies have found that in women, use of DHEA for months significantly raises serum testosterone but not estrogen levels, which can cause acne and growth of facial hair [ ].

The research to date does not support taking DHEA supplements to enhance exercise or athletic performance. The National Collegiate Athletic Association and the World Anti-Doping Agency ban the use of DHEA [ , ].

Ginseng is a generic term for botanicals from the genus Panax. Some popular varieties are known as Chinese, Korean, American, and Japanese ginseng.

Preparations made from ginseng roots have been used in traditional Chinese medicine for millennia as a tonic to improve stamina and vitality [ ]. So-called Siberian or Russian ginseng Eleutherococcus senticosus , although unrelated to Panax ginseng, has also been used in traditional Chinese medicine to combat fatigue and strengthen the immune system [ ].

Numerous small studies, with and without placebo controls, have investigated Panax ginseng's potential to improve the physical performance of athletes, regular and occasional exercisers, and largely sedentary individuals. In almost all cases, the studies found that Panax ginseng in various doses and preparations had no ergogenic effect on such measures as peak power output, time to exhaustion, perceived exertion, recovery from intense activity, oxygen consumption, or heart rate [ , ].

One review of studies of the effects of Siberian ginseng on endurance performance found that the five studies with the most rigorous research protocols with a total of 55 men and 24 women showed no effect of supplementation for up to 6 weeks on exercise performed for up to minutes [ ].

Short-term Panax ginseng use appears to be safe; the most commonly reported adverse effects include headache, sleep disturbances, and gastrointestinal disorders [ ]. Short-term Siberian ginseng use also appears to be safe.

The studies cited above reported no adverse effects, although other reports of clinical trials have listed insomnia as a rare side effect [ ].

The research to date provides little support for taking ginseng to enhance exercise or athletic performance [ , ]. Glutamine is a key molecule in metabolism and energy production, and it contributes nitrogen for many critical biochemical reactions [ ]. It is an EAA for critically ill patients when the body's need for glutamine exceeds its capacity to produce sufficient amounts.

Few studies have examined the effect of glutamine supplementation alone as an ergogenic aid [ ]. One study randomized 31 male and female weightlifters to receive either glutamine 0.

There were no significant differences between the two groups in measures of strength, torque, or lean tissue mass, demonstrating that glutamine had no effect on muscle performance, body composition, or muscle-protein degradation. Another study compared the effect of glutamine four doses of 0.

Supplementation with glutamine reduced the magnitude of strength loss, accelerated strength recovery, and diminished muscle soreness more quickly than placebo; these effects were more pronounced in the men.

Some athletes use glutamine supplements in the hope that they will attenuate exercise-induced immune impairment and reduce their risk of developing upper respiratory tract infections.

However, there is little research-based support for this benefit [ , ]. In the studies described above, the glutamine had no reported side effects. Many patients with serious catabolic illnesses, such as infections, intestinal diseases, and burns, take glutamine safely as part of their medical care.

Daily oral doses ranging from 0. The research to date does not support taking glutamine alone to improve exercise and athletic performance [ , ]. Iron is an essential mineral and a structural component of hemoglobin, an erythrocyte protein that transfers oxygen from the lungs to the tissues, and myoglobin, a protein in muscles that provides them with oxygen.

Iron is also necessary to metabolize substrates for energy as a component of cytochromes and to dehydrogenase enzymes involved in substrate oxidation [ ].

Iron deficiency impairs oxygen-carrying capacity and muscle function, and it limits people's ability to exercise and be active [ 12 , ]. Its detrimental effects can include fatigue and lethargy, lower aerobic capacity, and slower times in performance trials [ ].

Iron balance is an important consideration for athletes who must pay attention to both iron intakes and iron losses. Teenage girls and premenopausal women are at increased risk of obtaining insufficient amounts of iron from their diets. They require more iron than teenage boys and men because they lose considerable iron due to menstruation, and they might not eat sufficient amounts of iron-containing foods [ , ].

Athletes of both sexes lose additional iron for several reasons [ , , , ]. Physical activity produces acute inflammation that reduces iron absorption from the gut and iron use via a peptide, hepcidin, that regulates iron homeostasis. Iron is also lost in sweat. The destruction of erythrocytes in the feet because of frequent striking on hard surfaces leads to foot-strike hemolysis.

Also, use of anti-inflammatories and pain medications can lead to some blood loss from the gastrointestinal tract, thereby decreasing iron stores.

The richest dietary sources of heme iron which is highly bioavailable include lean meats and seafood. Plant-based foods—such as nuts, beans, vegetables, and fortified grain products—contain nonheme iron, which is less bioavailable than heme iron.

Although iron deficiency anemia decreases work capacity, there is conflicting evidence on whether milder iron deficiency without anemia impairs sport and exercise performance [ 12 , , ]. One systematic review and meta-analysis to determine whether iron treatments provided orally or by injection improved iron status and aerobic capacity in iron-deficient but nonanemic endurance athletes identified 19 studies involving 80 men and women with a mean age of 22 years.

Iron treatments improved iron status as expected, but they did not guarantee improvement in aerobic capacity or indices of endurance performance [ ].

Another systematic review and meta-analysis compared the effects of iron supplementation with no supplementation on exercise performance in women of reproductive age [ ].

Most of the 24 studies identified were small i. Based on the limited data and heterogenicity of results, the study authors suggested that preventing and treating iron deficiency could improve the performance of female athletes in sports that require endurance, maximal power output, and strength.

Athletes can safely obtain recommended intakes of iron by consuming a healthy diet containing iron-rich foods and by taking an iron-containing dietary supplement as needed.

High doses of iron may be prescribed for several weeks or months to treat iron deficiency, especially if anemia is present. Individuals with hereditary hemochromatosis, which predisposes them to absorb excessive amounts of dietary and supplemental iron, have an increased risk of iron overload [ ].

Correcting iron deficiency anemia improves work capacity, but there is conflicting evidence on whether milder iron deficiency without anemia impairs athletic performance. Furthermore, they warn that iron supplementation can cause gastrointestinal side effects. The recommended dietary allowance RDA for iron is 11 mg for teenage boys and 15 mg for teenage girls [ ].

The RDA is 8 mg for men and 18 mg for women age 50 and younger, and 8 mg for older adults of both sexes. Recommended intakes of iron for vegetarians and vegans are 1. More information on iron and the treatment of iron-deficiency anemia is available in the ODS health professional fact sheet on iron.

Protein is necessary to build, maintain, and repair muscle. Exercise increases intramuscular protein oxidation and breakdown, after which muscle-protein synthesis increases for up to a day or two [ ]. Regular resistance exercise results in the accretion of myofibrillar protein the predominant proteins in skeletal muscle and an increase in skeletal muscle fiber size.

Aerobic exercise leads to more modest protein accumulation in working muscle, primarily in the mitochondria, which enhances oxidative capacity oxygen use for future workouts [ , ].

Athletes must consider both protein quality and quantity to meet their needs for the nutrient. They must obtain EAAs from the diet or from supplementation to support muscle growth, maintenance, and repair [ ].

The nine EAAs are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. See other sections of this fact sheet for information on the amino acids arginine and glutamine as well as the BCAAs leucine, isoleucine, and valine.

The potential of these amino acids to enhance exercise and athletic performance is not related to their incorporation into proteins. Adequate protein in the diet is required to provide the EAAs necessary for muscle-protein synthesis and to minimize muscle-protein breakdown.

Dietary protein consumption increases the concentration of amino acids in the blood, which muscle cells then take up. Sufficient protein is necessary primarily to optimize the training response to, and the recovery period after, exercise [ 12 , ].

Muscle protein synthesis leading to increases in strength and muscle mass appears to be optimal with the consumption of high-quality protein providing about 10 g EAAs within 0—2 hours after exercise, in the early recovery phase [ 12 ].

However, a meta-analysis of randomized clinical trials found that ingesting protein within an hour before or after exercise does not significantly increase muscle strength or size or facilitate muscle repair or remodeling [ 77 ]. The period after exercise when protein intake reduces muscle protein breakdown, builds muscle, and increases mitochondrial proteins to enhance oxygen use by working muscles the so-called window of anabolic opportunity can last for up to 24 hours [ 79 ].

Participants in these studies consumed a bedtime drink containing Some studies show increased muscle protein synthesis when plasma levels of amino acids are raised [ 76 ]. The Food and Nutrition Board has not set a UL for protein, noting that the risk of adverse effects from excess protein from food is very low [ ].

However, it advises caution for those obtaining high protein intakes from foods and supplements because of the limited data on their potential adverse effects.

High-protein diets e. Protein increases urinary calcium excretion, but this appears to have no consequence for long-term bone health [ ] and, in any event, is easily compensated for by the consumption of slightly more calcium.

Many foods—including meats, poultry, seafood, eggs, dairy products, beans, and nuts—contain protein. Protein powders and drinks are also available, most of which contain whey, one of the complete proteins isolated from milk [ ].

Digestion of casein, the main complete protein in milk, is slower than that of whey, so the release of amino acids from casein into the blood is slower [ 72 ].

Soy protein lacks the EAA methionine and might lose some cysteine and lysine in processing; rice protein lacks the EAA isoleucine [ ]. Many protein supplements consist of a combination of these protein sources. All EAAs are necessary to stimulate muscle protein synthesis, so users should select singular or complementary protein sources accordingly.

To maximize muscle adaptations to training, the AND, DoC, and ACSM recommend that athletes consume 0. Since the Food and Nutrition Board developed the RDA for protein, more recent data have suggested that athletes require a daily protein intake of 1.

Athletes might benefit from even greater amounts for short periods of intense training or when they reduce their energy intake to improve physique or achieve a competition weight [ 12 ].

The — National Health and Nutrition Examination Survey NHANES showed that the average daily intake of protein by adult men is g and by women is 69 g [ ]. Athletes who require additional protein can obtain it by consuming more protein-containing foods and, if needed, protein supplements and protein-fortified food and beverage products.

Quercetin is a polyphenolic flavonol that is naturally present in a variety of fruits such as apples , vegetables such as onions , and beverages such as wine and, especially, tea.

The mechanisms by which quercetin might enhance exercise and athletic performance when taken in much larger amounts are not known, but many have been hypothesized. For example, quercetin might increase the number of mitochondria in muscle, reduce oxidative stress, decrease inflammation, and improve endothelial function blood flow [ , ].

Numerous small studies have assessed quercetin in supplemental form as a potential ergogenic aid in young adult, mostly male, participants. The effects of quercetin supplementation were inconsistent and varied by study, but they generally ranged from no ergogenic benefit to only a trivial or small improvement that might not be meaningful in real-world in contrast to laboratory exercise conditions [ 42 , , , ].

The safety of longer term use of that amount of quercetin or more has not been studied. More research, including larger clinical trials, on quercetin supplementation to improve aerobic capacity in trained athletes during specific sports and competitions is needed before any recommendations can be made [ ].

Ribose, a naturally occurring 5-carbon sugar synthesized by cells and found in some foods, is involved in the production of ATP [ 75 ]. The amount of ATP in muscle is limited, and it must continually be resynthesized. Therefore, theoretically, the more ribose in the body, the more potential ATP production [ ].

The authors of the short-term studies investigating ribose as a potential ergogenic aid have not reported any safety concerns. No studies have assessed the safety of long-term ribose use as a dietary supplement. Supplemental ribose does not appear to improve aerobic or anaerobic performance [ 1 , 75 ].

Sodium bicarbonate is commonly known as baking soda. The consumption of several teaspoons of sodium bicarbonate over a short time temporarily increases blood pH by acting as a buffering agent.

The precise mechanism by which this induced alkalosis leads to an ergogenic response to exercise is unclear. It is thought that bicarbonate loading enhances disposal of hydrogen ions that accumulate and efflux from working muscles as they generate energy in the form of ATP via anaerobic glycolysis from high-intensity exercise, thereby reducing the metabolic acidosis that contributes to fatigue [ , ].

As a result, supplementation with sodium bicarbonate might improve performance in short-term, intense exercises e. Many studies have assessed sodium bicarbonate as an ergogenic aid in swimmers, cyclists, rowers, boxers, tennis and rugby players, judo practitioners, and others [ ].

These studies usually included a small number of participants who underwent one or more trials in a laboratory over several days. Because the research results are conflicting, the activities and individuals most likely to benefit from sodium bicarbonate supplementation in real-world conditions is not clear.

However, individuals have varied responses to bicarbonate loading; the practice does not benefit some users, and it can worsen rather than enhance performance in others. Recreationally active individuals, in particular, might find the supplements to be ergogenic for one exercise session but not another.

Many study findings suggest that supplementation with sodium bicarbonate is most likely to improve the performance of trained athletes [ , ]. The main side effect of sodium bicarbonate supplementation in gram quantities is gastrointestinal distress, including nausea, stomach pain, diarrhea, and vomiting.

Supplement users can reduce or minimize this distress by consuming the total dose in smaller amounts multiple times over an hour with fluid and a snack of carbohydrate-rich food [ , ]. Sodium bicarbonate is Such a large intake of sodium with fluid can lead to temporary hyperhydration, which could be useful in activities where large sweat losses might otherwise lead to significant fluid deficits.

However, the slight increase in body weight from fluid retention might hinder performance in other sports [ ]. Studies have not evaluated the safety and effectiveness of long-term use of sodium bicarbonate as an ergogenic aid over months or longer.

Many athletes find this amount of sodium bicarbonate powder dissolved in fluid to be unpalatably salty [ ]. The Australian Institute of Sport supports the use of bicarbonate for improving sports performance in suitable athletic competitions under the direction of an expert in sports medicine, but it notes that more research might be required to understand how the supplement should be used for best results [ 29 ].

The Montmorency variety of tart or sour cherry Prunus cerasus contains anthocyanins and other polyphenolic phytochemicals, such as quercetin. Researchers hypothesize that these compounds have anti-inflammatory and antioxidant effects that might facilitate exercise recovery by reducing pain and inflammation, strength loss and muscle damage from intense activity, and hyperventilation trauma from endurance activities [ ].

The labels on tart-cherry juice and concentrate products do not usually indicate that they are dietary supplements, although the labels on products containing encapsulated tart-cherry powder do.

Much of the limited research on use of tart cherry to enhance exercise and athletic performance involves short-term use of a tart-cherry product or placebo by young resistance-trained men for about a week before a test of strength such as single-leg extensions or back squats ; participants continue taking the supplements for about 2 days after the test.

None of the participants who drank the juice experienced airway inflammation causing upper respiratory tract symptoms after the marathon a common complaint in many marathon runners , but half of those drinking the placebo did. Another study compared a supplement containing mg freeze-dried Montmorency tart-cherry-skin powder CherryPURE with a placebo in 18 male and 9 female endurance-trained runners and triathletes age range 18—26 years [ ].

Participants took the supplements once a day for 10 days, including the day they ran a half-marathon, then for 2 days after the run. Further research is needed to determine the value of tart-cherry products for enhancing performance and recovery from intense exercise or participation in sports—especially when used on a regular basis—and the amounts of supplement, juice, or concentrate needed to provide any benefits.

Studies have not identified any side effects of the fresh tart-cherry juice or concentrate or of supplements of dried tart-cherry-skin powder.

However, they have not adequately assessed the safety of tart-cherry dietary supplements. There is no expert consensus on the value of taking tart-cherry products to enhance exercise and athletic performance.

Tribulus terrestris common names include bindii, goat's-head, bullhead, and tackweed , is a fruit-bearing plant that is most common in Africa, Asia, Australia, and Europe. It has been used since ancient times in Greece, China, and Asia to treat low libido and infertility [ ].

Tribulus terrestris extracts contain many compounds, including steroidal saponins [ ]. Some marketers claim that Tribulus terrestris enhances exercise and athletic performance by increasing serum concentrations of testosterone and luteinizing hormone, but studies have not adequately determined its potential mechanisms of action [ ].

Only a few small, short-term clinical trials have investigated Tribulus terrestris as an ergogenic aid [ ], and none since A study in 15 resistance-trained men found no differences among those taking 3.

In 22 elite male rugby players age The only toxicity studies of Tribulus terrestris were conducted in animals, where unspecified high intakes led to severe heart, liver, and kidney damage [ ].

The clinical studies described above found no side effects of Tribulus terrestris. Subsequent tests indicated hepatotoxicity, nephrotoxicity, and neurotoxicity. The man's condition improved after he discontinued the water, but the water was not tested to determine the presence or amount of Tribulus terrestris or any other potential toxin or contaminant.

The Australian Institute of Sport advises against the use of Tribulus terrestris by athletes, noting that this supplement and other claimed testosterone boosters are banned from athletic competitions or have a high risk of being contaminated with substances that, if ingested, could lead to positive drug-screening results [ ].

The published biomedical literature provides no support for the efficacy and insufficient support for the safety of Tribulus terrestris for enhancing exercise performance [ ].

This section provides examples of ingredients that FDA currently prohibits in dietary supplements and that some consumers have used in the past as ergogenic aids, despite the lack of evidence supporting their use.

Androstenedione is an anabolic steroid precursor, or prohormone, that the body converts to testosterone which induces muscle growth and estrogen [ ]. Major League Baseball slugger Mark McGwire popularized androstenedione as an ergogenic aid in [ ]. However, two randomized clinical trials found no performance benefits from androstenedione supplements.

In one study, 10 healthy young men age 19—29 years took a single mg dose of androstenedione. The short-term or longer term use of the supplement did not affect serum testosterone concentrations, nor did it produce any significantly greater gains in resistance-training performance, muscle strength, or lean body mass.

However, participants who took androstenedione for the 6 weeks experienced significant declines in their high-density lipoprotein HDL cholesterol levels and significant increases in serum estrogens. The supplements did not improve participants' muscular strength or lean body mass compared with placebo, but they significantly decreased HDL cholesterol levels and raised levels of serum estrogens.

In March , FDA warned companies to cease distributing androstenedione-containing dietary supplements. The rationale was the lack of sufficient information to establish that such products could reasonably be expected to be safe and that FDA had never approved androstenedione as a new dietary ingredient permitted in supplements [ ].

Department of Justice classified androstenedione as a Schedule III controlled substance defined as a drug with a moderate to low potential for physical and psychological dependence in [ ].

The National Collegiate Athletic Association, International Olympic Committee, and World Anti-Doping Agency ban the use of androstenedione [ , ]. Dimethylamylamine DMAA is a stimulant formerly included in some preworkout and other dietary supplements claimed to enhance exercise performance and build muscle.

Studies have not evaluated DMAA in humans as a potential ergogenic aid. In , FDA declared products containing this ingredient to be illegal after it received 86 reports of deaths and illnesses associated with dietary supplements containing DMAA.

These reports described heart problems as well as nervous system and psychiatric disorders [ ]. Furthermore, FDA had never approved DMAA as a new dietary ingredient that would reasonably be expected to be safe [ ].

Although products marketed as dietary supplements containing DMAA are illegal in the United States, discontinued, reformulated, or even new products containing DMAA might still be found in the U. The Department of Defense's Human Performance Resource Center maintains a list of currently available products that contain DMAA or are labeled as containing DMAA, dimethylamylamine, or an equivalent chemical or marketing name e.

FDA also determined that dietary supplements containing 1,3-dimethybutylamine DMBA , a stimulant chemically related to DMAA, are adulterated. As with DMAA, FDA had never approved this stimulant as a new dietary ingredient. The agency contended that there is no history of use or data offering sufficient assurance that this compound is not associated with a significant or unreasonable risk of illness or injury [ , ].

Ephedra also known as ma huang , a plant native to China, contains ephedrine alkaloids, which are stimulant compounds; the primary alkaloid is ephedrine [ ]. In the s, ephedra—frequently combined with caffeine—was a popular ingredient in dietary supplements sold to enhance exercise and athletic performance and to promote weight loss.

No studies have evaluated the use of ephedra dietary supplements, with or without caffeine, as ergogenic aids. Instead, available studies have used the related synthetic compound ephedrine together with caffeine and typically measured the effects 1—2 hours after a single dose [ , ].

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