Creatine remains a popular supplement due to its legality and record of relative safety. Its ergogenic potential lies in the enhanced utilization of phosphocreatine (PCr) to generate ATP anaerobically, and possibly accelerated resynthesis of PCr during rest periods between heavy bouts of exercise. Its effectiveness as an ergogenic aid remains controversial, since most studies with favorable results have been on stationary cycles in laboratory settings, as opposed to “on the field” or “on the ice” performance. Furthermore, creatine's efficacy is limited to the anaerobic (all-out sprint) state, and sports such as ice hockey involve a combination of aerobic and anaerobic activity. Still, creatine supplementation may have applicability to ice hockey because players skate in shifts and do require anaerobic bursts of speed. The water weight gain which creatine causes may explain why studies on runners and swimmers have been unconvincing of an ergogenic effect, but this may be less of an issue in skaters. Short-term administration of creatine has been found to increase muscle compartment pressures in the leg, due to water retention. This is the likely explanation for the numerous reported complaints of muscle cramping. Gastrointestinal tolerability and renal overload are also areas of concern. Although creatine has not been found to cause serious side effects when consumed at recommended doses for 8 weeks or less, most subjects take creatine at much higher doses than recommended. Long-term safety is not established. Another concern with creatine, as with all supplements, is that it is not classified as a drug and therefore can bypass Food and Drug Administration (FDA) scrutiny for product claims of efficacy, safety, and purity.