Am Fam Physician. 2001;63(5):913-923
Numerous ergogenic aids that claim to enhance sports performance are used by amateur and professional athletes. Approximately 50 percent of the general population have reported taking some form of dietary supplements, while 76 to 100 percent of athletes in some sports are reported to use them. Physicians can evaluate these products by examining four factors (method of action, available research, adverse effects, legality) that will help them counsel patients. Common ergogenic aids include anabolic steroids, which increase muscle mass. These illegal supplements are associated with a number of serious adverse effects, some irreversible. Creatine modestly improves athletic performance and appears to be relatively safe. Dehydroepiandrosterone and androstenedione do not improve athletic performance but apparently have similar adverse effects as testosterone and are also banned by some sports organizations. Caffeine has mild benefits and side effects and is banned above certain levels. Products that combine caffeine with other stimulants (e.g., ephedrine) have been linked to fatal events. Protein and carbohydrate supplementation provides modest benefits with no major adverse effects.
Ergogenic aids are substances or devices that enhance energy production, use or recovery and provide athletes with a competitive advantage.
Numerous products claim to bolster strength or endurance in sports. In 1996, approximately 50 percent of the general population reported some supplement use.1 Other surveys have shown that 76 percent of college athletes, and 100 percent of body builders take supplements.2 Americans spent $11.8 billion on supplements in 1997, with a predicted growth rate of 10 to 14 percent in 2000 (Table 1).3
|Creatine powder||$ 26|
|Protein powder (50 g daily)||85|
|Multivitamins||5 to 20|
New products with ergogenic claims appear on the market almost daily. Most are classified as supplements, which means the contents of the product and the claims on the label have not been evaluated by the U.S. Food and Drug Administration and may not have any scientific basis. The following questions will help the physician and patient determine whether a product is worth taking:
1. What is the physiologic basis or theory for this product's action?
2. Are there any scientific studies published in peer-reviewed journals that support or refute the claims that the product makes?
3. Are there any side effects, especially any potentially serious adverse effects?
4. Is the product legal?4
This article reviews some of the more popular supplements and provides some basic information on others.
Anabolic steroids are testosterone derivatives with three mechanisms of action. First, anticatabolic effects reverse the actions of glucocorticoids and help metabolize ingested proteins, converting a negative nitrogen balance into a positive one. Second, anabolic effects directly induce skeletal muscle synthesis. Third, there is a “steroid rush”—a state of euphoria and decreased fatigue that allows the athlete to train harder and longer.5
Many early studies used physiologic doses, or doses only two to three times these amounts, and provided mixed results. More recent reviews,5 controlling for various measurement methods, have concluded that anabolic steroids do indeed cause increased strength and muscle mass. A randomized, double-blind, 10-week study6 of 40 men examined the effect of supraphysiologic testosterone doses. The participants were divided into four groups: those given a placebo with or without weight training, and those given 600-mg testosterone enanthate with or without weight training. Diet and training times were controlled. Fat-free mass, muscle size and strength increased more than placebo in both groups taking testosterone than in the groups taking placebo. The subjects in the exercise plus testosterone group had a 9 percent increase in mass and 23 percent increase in bench-press strength, compared with 3 percent and 9 percent, respectively, in the subjects in the exercise plus placebo group.6 These doses were comparable with the doses that many athletes who use steroids take.
Anabolic steroids have many adverse effects, most related to the unwanted androgenic effects. Some of the adverse effects are potentially serious and irreversible (Table 2).
|Reversible side effects|
|Increased or decreased libido|
|Decreased sperm production|
|Serious and irreversible side effects|
|Hypertension from mineralocorticoid effects|
|Dysplastic changes in collagen fibrils, resulting in severe tendon ruptures|
|Liver tumors (hepatocellular carcinoma, hepatic adenoma, hepatic cholangiocarcinoma)|
|Psychosis (i.e., “steroid rage”)|
|Irreversible hirsutism, clitoral hypertrophy and deepening of voice in women|
|Premature closure of growth plates, causing shorter stature in adolescents|
Anabolic steroids such as testosterone and its derivatives are prescription medications with clearly defined indications. Procuring and using them without a prescription is illegal. Most sports organizations have rules that ban the use of anabolic steroids for any reason.
During brief, high intensity exercise, adenosine diphosphate is rephosphorylated to adenosine triphosphate (ATP) by muscle phosphocreatine stores. As muscle phosphocreatine stores become depleted, performance decreases. Oral creatine supplementation can increase muscle phosphocreatine stores by 6 to 8 percent. Increasing the available muscle stores of phosphocreatine causes faster regeneration of ATP, allowing decreased rest time between activities and increased energy for repeated bouts of exercise. Increased muscle creatine also buffers the lactic acid produced during exercise, delaying muscle fatigue and soreness. As with any ergogenic aid, increased motivation can spring from expected or perceived benefits, causing increased effort (placebo effect).
Creatine research shows generally positive results. A short-term, double-blind, placebo-controlled study7 examined the effects of 28 days of creatine supplementation on 25 football players. Diet and exercise were tightly controlled, and strength and body composition were measured. Body weight, dual-energy radiograph absorptiometry-scanned body mass, fat-free and bone-free mass, and bench-press strength all increased in the athletes taking creatine. Overall lifting volume (sum of all lifts) was increased by 41 percent in this group. A five-week study8 of 42 football players also showed gains in strength and mass. Another report9 of 19 women who took supplements for 10 weeks also described increases in strength and mass. Some researchers10,11 have seen strength gains with as little as five to seven days of supplementation.10,11 Studies12 examining the effects of creatine in older individuals (60 to 82 years of age) have found no effect on body composition or strength. Investigations7,13 of the benefits on short-term sprint performance have shown increases in endurance time. A summary of 31 studies14 on sprint performance showed that supplemental creatine is associated with some improvement in athletic performance in laboratory settings, but most findings indicated no benefit on the field.
A typical regimen for creatine supplementation uses a loading dosage of 20 g daily, divided in four doses, for five to seven days, followed by a maintenance dosage of 5 g daily. Creatine monohydrate is not dehydrating, and may be safer.
Weight gain is the most consistent adverse effect reported. In studies that investigated side effects, no other adverse effects were found, including no changes in electrolyte concentrations, muscle cramps or strains.7 Researchers15 examined the renal function of patients who had been using creatine for as long as five years and found no detrimental effects.15 Some studies have shown improved cholesterol profiles in persons taking creatine.7 It must be noted, however, that most research to date has examined creatine use of three months or less, leaving questions about long-term use unanswered.
Creatine is legal for use in amateur and professional sports.
Dehydroepiandrosterone and Androstenedione
Both of these supplements are precursors in the gonadal steroid pathway (Figure 1). Increasing supplies of precursors theoretically cause a physiologic increase in testosterone synthesis.
Dehydroepiandrosterone (DHEA) has been studied for its replacement role in older men and women. These studies16,17 found testosterone levels increased in women, but were unchanged in men, with no changes in body composition noted. No published studies of its ergogenic benefit in younger athletes exist. One eight-week study18 evaluated androstenedione supplementation in 30 men, aged 19 to 29 years, during resistance training. No differences in muscle size, strength or overall body composition were noted. One study19 has shown transient increases in serum testosterone levels but no ergogenic benefit has been demonstrated.
No long-term studies of adverse effects are available. If these precursors could successfully increase testosterone production, they would likely cause the many adverse effects associated with anabolic steroids.
DHEA is banned by the International Olympic Committee (IOC). Androstenedione is banned by the IOC, the National Collegiate Athletic Association (NCAA) and the National Football League.
Caffeine enhances the contractility of skeletal and cardiac muscle, and helps metabolize fat, thereby sparing muscle glycogen stores. It is also a central nervous system stimulant, which can aid in activities that require concentration.
Ergogenic doses of caffeine may cause restlessness, nervousness, insomnia, tremors, hyperesthesia and diuresis. Caffeine use has no adverse effects on body temperature or sweating.23
Caffeine is part of a regular diet for most people and is legal to a certain level. The legal urine level for athletes is 12 μg per mL (IOC standards) or 15 μg per mL (NCAA standards). The ergogenic dose is approximately one half of this—250 to 500 mg (three cups of coffee or six to eight sodas). Many athletes take caffeine in pill form.
Caffeine and Ephedrine Combination
Sympathomimetics such as ephedrine, pseudoephedrine, phenylpropanolamine and herbal ephedrine (ma huang) are used for their stimulant properties. This combination is found in many “energizing” and diet supplements and is used to increase subjective energy, decrease appetite and increase metabolism without exercise.24
The combined adverse effects of these stimulants include restlessness, nervousness, tachycardia, arrhythmias and hypertension. As of August 1998, at least 17 deaths have been linked to use of these products in combination.26
Use of ephedrine products and elevated levels of urinary caffeine, as noted above, are banned by the IOC.
Protein and its constituent, amino acids, are the building blocks of muscle. Protein supplements are used by some athletes to enhance muscle repair and growth. Inadequate protein intake does cause a negative nitrogen balance, which slows muscle growth and causes fatigue.
Athletes in training have increased protein needs. A study27 examining the protein requirements of experienced resistance-training athletes found that those consuming the recommended daily allowance for protein (0.8 g per kg daily) had a negative nitrogen balance. The protein intake required for a zero balance was 1.4 g per kg daily, with a recommended intake of 1.8 g per kg daily. Another study28 using novice resistance-training athletes found their requirements to be 1.6 to 1.7 g per kg daily. Both studies found that protein intakes in excess of these recommendations did not provide additional gains in strength or mass.
In an athlete with normal renal function, there are no notable adverse effects to increased protein consumption. It may be more healthy, however, to avoid acquiring protein from foods that also contain increased amounts of fat and cholesterol.
Protein supplements are legal.
While fat stores constitute the largest reservoir of stored energy, carbohydrates are the body's main source of rapidly available energy. It has been suggested that taking proper quantities of carbohydrates at the right time could improve athletic performance by ensuring adequate energy stores are available when necessary.
Loading, or increasing the carbohydrate content of the diet for several days before an event, has been promoted as a means to prolong exercise endurance. One study29 evaluated its impact on continuous, short-term events of less than one hour and found no benefit, because muscle glycogen content was not depleted at the end of the exercise.
A meal prior to exercise will ensure that muscle and liver glycogen stores are maximized. Studies30,31 investigating a meal two to four hours prior to exercise have shown positive effect, regardless of the “glycemic index” of the foods ingested. Evaluation of six endurance athletes ingesting carbohydrates only 45 minutes prior to a two-hour exercise test revealed no benefit.32
Replenishment with carbohydrate-containing fluids during an endurance event may help to delay fatigue. Thirty marathon runners in a double-blind study33 described decreased subjective exertion when ingesting 60 g per hour of a liquid carbohydrate solution during a two and one-half hour run. Another study34 found that ingesting a carbohydrate-electrolyte drink during one hour of high-intensity exercise improved performance in 19 bicyclists. Many studies have demonstrated similar results. One study35 that evaluated solid versus liquid carbohydrate replenishment showed no difference, as long as adequate water intake was maintained. Eating a mixture of carbohydrates and protein within two hours after an activity has also been associated with benefits, including replenishment of depleted muscle and liver glycogen stores and decreased muscle catabolism. A study36 of nine weight lifters showed increased levels of plasma growth hormone and insulin when athletes ingested protein and carbohydrate immediately and two hours after exercise, which would theoretically provide a physiologic environment favorable for muscle growth. Another placebo-controlled study37 of endurance athletes ingesting a carbohydrate-containing solution after exercise reported increased glycogen resynthesis.
Theoretic disadvantages have been reported with carbohydrate supplementation. Increased insulin levels after carbohydrate consumption were shown to significantly decrease blood glucose levels in some athletes, though not all athletes seem to be subjectively sensitive to these decreased levels.38 Fructose-containing solutions have been associated with adverse gastrointestinal effects in some studies.39
Carbohydrate supplements are legal.
Many other dietary supplements have been advertised for their purported ergogenic properties, and the list grows each year. Table 3 provides a brief summary of the most common agents that physicians may hear about from their patients who are athletes. When counseling patients about ergogenic aids, it is important that the physician be knowledgeable about the topic. The intervention that carries the most impact is ensuring optimal dietary habits. Supplying adequate energy intake, carbohydrates and protein in the diet, and timing these to be efficiently used by the body, will provide the most effective and safe results.36,40
|Ergogenic aid||Action||Research on ergogenic effects||Side effects||Legality|
|Alcohol||Decreases anxiety||No benefits||Significant||Banned for shooting events|
|Amphetamines||Improve concentration, decrease fatigue and appetite||Mixed, some positive||Significant, dangerous||Illegal|
|Anabolic steroids||Increase strength, lean muscle mass and motivation||Positive||Significant, dangerous||Illegal|
|Androstenediol||Same as steroids||Limited, refutes||Unknown||Banned by IOC|
|Androstenedione||Same as steroids||Refutes, no benefits||Significant||Banned by IOC, NCAA|
|Antioxidants||Decrease muscle breakdown||Mixed, no clear benefits||Mild at high doses||Legal|
|Arginine, ornithine, lysine||Stimulate growth hormone release||No benefit||None at doses used||Legal|
|Aspartates||Increase free fatty acid use, sparing muscle glycogen||Mixed, some positive benefits||Mild at high doses||Legal|
|Aspirin||Decreases pain with muscle fatigue and muscle breakdown||No benefit||Mild||Legal|
|Avena sativa||Increases steroid production||Limited, refutes||None||Legal|
|Bee pollen||Increases strength and endurance||Refutes, no benefits||Allergic reaction||Legal|
|Beta blockers||Decrease anxiety||Positive effect on fine motor control, negative effect on aerobic capacity||Significant||Banned by IOC|
|Beta2 agonists||Increase lean muscle mass||Mixed, no benefit from inhaled formulations||Mild||Banned by IOC, legal when prescribed|
|Blood doping||Increases aerobic capacity||Supports||Significant, dangerous||Illegal|
|Boron||Increases endogenous steroid production||Refutes, no benefit||Mild at high doses||Legal|
|Branched chain amino acids||Decrease mental fatigue||Mixed, negative||Mild at high doses||Legal|
|Caffeine||Increases muscle contractility and aerobic endurance, enhances fat metabolism||Supports||Mild||Legal to urine level of 12 to 15 μg per mL|
|Calcium||Increases muscle contractility, enhances glycogen metabolism||Refutes, no benefit||Mild at high doses||Legal|
|Carbohydrates||Increase endurance, decrease fatigue||Supports||Mild at high doses||Legal|
|Carnitine||Increases fat metabolism||Refutes||None||Legal|
|Choline||Increases endurance||Mixed, inconclusive||None||Legal|
|Chromium||Increases lean mass||Refutes, no benefit unless prior deficiency||Safe to 400 μg daily, potentially dangerous above this level||Legal|
|Chrysin||Inhibits aromatase, increases endogenous steroids||Limited, refutes||None||Legal|
|Cocaine||Stimulates CNS, delays fatigue||Mixed||Significant, dangerous||Illegal|
|Coenzyme Q10 (ubiquinone)||Delays fatigue, acts as antioxidant||Refutes, no benefit||None||Legal|
|Coenzyme Q12||Increases aerobic capacity, speeds muscle repair||Refutes, no benefit||None||Legal|
|Creatine||Increases muscle energy, endurance, strength and lean muscle mass||Supports, insufficient data on long-term use||Mild||Legal|
|DHEA||Increases endogenous steroid production||No benefit in healthy athletes||Potentially dangerous||Banned by IOC, some other organizations|
|Diuretics||Decrease body mass||Limited benefit||Potentially dangerous||Banned by IOC|
|Ephedrine, other sympathomimetics||Stimulate CNS, increase energy, delay fatigue, stimulate weight loss||No benefit||Potentially dangerous||Banned by IOC, some other organizations|
|Ephedrine plus caffeine||Increases energy, stimulates weight loss||Supports||Potentially dangerous, fatal at high doses||Banned by IOC, some other organizations|
|Erythropoietin||Increases aerobic capacity||Supports||Significant, dangerous||Illegal|
|Fat supplements||Increase endurance||Refutes||Mild||Legal|
|Folic acid||Increases aerobic capacity||Refutes||None||Legal|
|GHB||Stimulates growth hormone release and muscle growth||Limited, refutes||Significant, dose-related; abuse potential||Illegal|
|Ginseng||Increases endurance, enhances muscle recovery||Limited, refutes, no benefit||Mild, abuse syndrome reported||Legal|
|Glucosamine||Serves as NSAID alternative, enhances recovery||Limited, may have limited NSAID abilities||None||Legal|
|Glutamine||Boosts immunity and growth hormone levels||May boost immunity, no other benefits||None||Legal|
|Glycerol||Improves hydration and endurance||Limited, supports||Mild||Legal (oral)|
|Guarana (herbal caffeine)||Same as caffeine|
|HMB||Decreases muscle breakdown, enhances recovery||Limited, some strength benefits||None||Legal|
|Human growth hormone||Anabolic effect on muscle growth, increases fat metabolism||Refutes, limited ergogenic benefits||Significant, dangerous||Illegal|
|Inosine||Enhances energy production, improves aerobic capacity||Refutes, no benefit||Mild||Legal|
|Iron||Increases aerobic capacity||No benefit unless preexisting deficiency||Mild, toxic at high doses||Legal|
|Leucine||Decreases muscle breakdown and spare muscle glycogen stores||Limited, no ergogenic effect||None||Legal|
|Ma huang (herbal ephedrine)||Same as ephedrine|
|Magnesium||Enhances muscle growth||No benefit unless preexisting deficiency||Mild at high doses||Legal|
|Marijuana||Decreases anxiety||Refutes, negative effect||Significant, dangerous||Illegal|
|Multivitamins||Increases energy, endurance and aerobic capacity, enhances recovery||No benefit unless preexisting deficiency||None at RDA, some toxicities at high doses||Legal|
|Narcotics||Increase endurance by suppressing pain, decrease anxiety||Mixed, negative||Significant, dangerous||Illegal|
|Niacin||Increases energy and endurance||No benefit unless a preexisting deficiency||Mild at high doses||Legal|
|Oxygen||Increases aerobic capacity, enhances recovery||No benefit if given before or after activity||Mild||Legal|
|Phosphates||Increase ATP production, energy and muscle endurance||Mixed, negative||Mild at high doses||Legal|
|Phytosterols||Stimulates release of endogenous steroids and growth hormone||Refutes, no benefit||Little data, allergic reaction possible||Legal|
|Protein||Optimizes muscular growth and repair||Supports, increased need for protein with activity||None unless underlying medical condition||Legal|
|Pycnogenol||Boosts antioxidant levels, enhances recovery||Supports, dietary sources offer same benefit||None||Legal|
|Pyruvate||Increases lean body mass||Limited research, benefit only in specific cases||None||Legal|
|D-Ribose||Increases cellular ATP and muscle power||No human research||None known||Legal|
|Selenium||Enhances antioxidant functions||Limited, no benefit||Mild at high doses||Legal|
|Sodium bicarbonate||Buffers lactic acid production, delays fatigue||Supports||Mild, dangerous at high doses||Legal|
|Strychnine||Unknown||No research on ergogenic benefits||Significant, dangerous||Legal|
|Tribulus terrestris||Increases endogenous steroid production||Refutes||Potentially dangerous at high doses||Legal|
|Tryptophan||Decreases pain perception, increases endurance||Mixed, no benefit in trained athletes||Mild, potentially dangerous||Legal|
|Vanadyl sulfate||Increases glycogen synthesis, enhances muscle recovery||Refutes, no benefit in healthy individuals||Mild||Legal|
|Vitamin B1 (thiamin)||Enhances energy production, increases aerobic capacity, improves concentration||No benefit unless preexisting deficiency||None||Legal|
|Vitamin B2 (riboflavin)||Increases aerobic endurance||No benefit unless preexisting deficiency||None||Legal|
|Vitamin B6 (pyridoxine)||Enhances muscle growth, decreases anxiety||No benefit unless preexisting deficiency||Mild at high doses||Legal|
|Vitamin B12 (cyanocobalamin)||Enhances muscle growth||No benefit unless preexisting deficiency||None||Legal|
|Vitamin B15 (dimethylglycine)||Increases muscle energy production||Mixed, negative||None proven, but concerns raised||Legal|
|Vitamin C||Acts as antioxidant, increases aerobic capacity and energy production||No benefit unless preexisting deficiency||Mild at high doses||Legal|
|Vitamin E||Acts as antioxidant, improves aerobic capacity||Mixed, some positive||Mild||Legal|
|Yohimbine||Increases endogenous steroid production||Refutes, no benefit||Mild||Legal|
|Zinc||Enhances muscle growth, increases aerobic capacity||Limited, negative||Mild||Legal|
If a patient asks about a specific ergogenic aid, he or she should be told what is known and unknown about the product based on current research, including the side effect profile. The danger is that once athletes start using a commercial supplement, they will continue to use more, eventually trying something that may not be safe. Many athletes feel pressured to use supplements to maintain a competitive advantage over their supplement-using peers. If physicians can guide athletes away from disproven and dangerous supplements, while maintaining open and honest lines of communication, then more serious health risks may be prevented.