In the competitive world of sports, the smallest advantage can make an enormous difference in the outcome of a contest. A substance that improves an athlete's strength, speed, or endurance is called an ergogenic aid.

The most effective ergogenic aids are both dangerous and illegal: stimulants, anabolic steroids, and human growth hormone. Numerous natural options are marketed as alternatives. In this article, we explore the many supplements used in the hopes of improving sports performance.

For additional sports-related articles, see Sports and Fitness Support: Enhancing Recovery and Sports Injuries.

Two natural supplements have shown meaningful promise as ergogenic aids: creatine and HMB.


Creatine, one of the best-selling and best-documented supplements for enhancing athletic performance, is a naturally occurring substance that plays an important role in the production of energy in the body. The body converts creatine 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.

However, the balance of current evidence suggests that that if creatine supplements have any benefit for sports performance, it is slight and limited to highly specific forms of exercise.

Several small double-blind studies have found that creatine can improve performance in exercises that involve repeated short bursts of high-intensity activity with intervening rest periods of adequate length.

For example, a double-blind, placebo-controlledstudy investigated creatine and swimming performance in 18 men and 14 women.1 Men taking the supplement had significant increases in speed when doing six bouts of 50-meter swims started at 3-minute intervals, compared to men taking placebo. However, their speed did not improve when swimming 10 sets of 25-yard lengths started at 1-minute intervals. Researchers theorize 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 the difference between the genders in response to creatine.

In an earlier double-blind study, 16 physical education students carried out ten 6-second bursts of extremely intense exercise on a stationary bicycle, separated by 30 seconds of rest.2The results showed that the students 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.2-4However, there have been negative results as well; in general, minimal to no benefits have been seen in studies involving athletes engaged in normal sports rather than contrived laboratory tests.2-7,143-146

In contrast, studies of endurance or nonrepetitive aerobic burst exercise generally have not shown benefits from creatine supplementation.6,8-11,147-148 Therefore, creatine probably will not help you with marathon running or single sprints.

Besides repetitive burst exercise, creatine has also shown promise for increasing isometric exercise capacity (pushing against a fixed resistance), in some, but not all studies.4,12-13,149-151In addition, two double-blind, placebo-controlled studies, each lasting 28 days, provide some evidence that creatine as well as creatine plus hydroxymethyl butyrate (HMB) (see below) can increase lean muscle and bone mass.14However, one double-blind trial failed to find creatine helpful for enhancing general fitness, including resistance exercise performance, in male seniors.125

The contradictory results seen in these small trials suggest that creatine offers at most a very modest sports performance benefit. For more information, including dosage and safety issues, see the full Creatine article.

Hydroxymethyl Butyrate

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. Some evidence suggests that taking HMB supplements might signal the body to slow down the destruction of muscle tissue.15 On this basis, HMB has been studied as a sports performance supplement for enhancing strength and muscle mass.

According to many (but not all) of the small double-blind trials that have been reported, HMB appears to improve muscle-growth response to weight training.14-20

For example, in a controlledstudy, 41 male volunteers aged 19 to 29 were given either 0, 1.5, or 3 g of HMB daily for 3 weeks.17 The participants also lifted weights 3 days a week according to a defined (rather severe) schedule. 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 or placebo daily, 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 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.

Similarly, a double-blind, placebo-controlled trial of 39 men and 36 women found that over 4 weeks, HMB supplementation improved response to weight training.19

Two placebo-controlled studies of 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.18In addition, a double-blind study of 31 men and women, all 70 years old and undergoing resistance training, found significant improvements in fat-free mass attributable to the use of HMB (3 g daily).21

However, there have been negative studies as well.14,20,22

All of these studies were small and therefore, their results are ultimately not terribly 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.