The purpose of this study was to investigate the effects of long-term creatine (Cr) supplementation on the aerobic capacity, repeated high-intensity exercise performance and muscle mass. Ten decathlon athletes were divided into Cr (n=5) and placebo (P, n=5) groups. The Cr group was orally administered 20g Cr monohydrate (Cr.H₂O) per day for 6 days followed by 4g per day for 7 weeks. The P group was administered the same amount of glucose polymer. No apparent difference in training quality or quantity was seen between the Cr and P groups. After supplementation, the phosphocreatine (PCr) concentration of the quadriceps muscle increased by 20% in the Cr group (P<0.01) but did not change in the P group. The time constant of PCr recovery after moderate exercise inside a magnetic resonance scanner was not altered by supplementation in either group. After supplementation, the Cr group maintained a higher PCr concentration and intracellular pH during high-intensity exercise and recovery than those before supplementation (P<0.05). Maximal oxygen uptake determined by treadmill running did not change in either group. In three bouts of 30 maximal isokinetic knee extension, peak torque production in the Cr group was greater during the latter 10 or 20 contractions of all bouts when compared with the corresponding measurements made before ingestion. Muscle cross-sectional area of the thigh increased in the Cr group during supplementation (P<0.05), whereas no change was found in the P group. These results suggest that relative long-term Cr supplementation does not enhance general or local aerobic capacity. In addition, these findings confirm that Cr ingestion improves repeated high-intensity exercise performance and promotes muscle hypertrophy.

DESCENTE SPORTS SCIENCE Vol.20/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE