van Loon, L. J., Oosterlaar, A. M., Hartgens, F., Hesselink, M. K., Snow, R. J., Wagenmakers, A. J. (2003). Effects of creatine loading and prolonged creatine supplementation on body composition, fuel selection, sprint and endurance performance in humans. Clinical Science, 104, 153-162.

This study assessed the effects of both creatine loading and prolonged supplementation on muscle creatine content, body composition, muscle and whole-body oxidative capacity, substrate utilization during submaximal exercise, and on repeated supramaximal sprint, as well as endurance-type time-trial performance on a cycle ergometer. Ss (N = 20) ingested creatine or a placebo during a 5-day loading period (20 g/day) after which supplementation was continued for up to six weeks (2 g/day).

Creatine loading increased muscle free creatine, creatine phosphate, and total creatine content. The subsequent use of a 2 g/day maintenance dose, as suggested by an American College of Sports Medicine Roundtable, resulted in a decline in both the elevated creatine phosphate and total creatine content and maintenance of the free creatine concentration. Both short- and long-term creatine supplementation improved performance during repeated supramaximal sprints on a cycle ergometer. However, whole-body and muscle oxidative capacity, substrate utilization and time-trial performance were not affected. The increase in body mass following creatine loading was maintained after six weeks of continued supplementation and accounted for by a corresponding increase in fat-free mass.

Implication. Prolonged creatine supplementation in humans does not increase muscle or whole-body oxidative capacity and, as such, does not influence substrate utilization or performance during endurance cycling exercise. Performance of supramaximal sprints is improved. It is suggested that prolonged creatine ingestion induces an increase in fat-free mass.

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