Effect of exogenous creatine supplementation on muscle PCr metabolism

P-31 NMR was used to assess the influence of two weeks creatine supplementation (21 g . d(-1)) on resting muscle PCr concentration, on the rate of PCr repletion (R-depl), and on the halftime of PCr repletion (t(1/2)). Body mass (BM) and volume of body water compartments were also estimated by impedance spectroscopy. Fourteen healthy male subjects (20.8 +/- 1.9 y) participated in this double-blind study. PCr was measured using a surface coil placed under the calf muscle, at rest and during two exercise bout the duration of which was 1 min. They were interspaced by a recovery of 10 min. The exercises comprised of 50 plantar flexions-extensions against weights corresponding to 40 % and 70 % of maximal voluntary contraction (MVC), respectively. Creatine supplementation increased resting muscle PCr content by similar to 20 % (P = 0.002), R-depl was also increased by similar to 15 % (P < 0.001) and similar to 10 % (P = 0.026) during 40 % and 70 % MVC exercises, respectively. No change was observed in R-repl and t(1/2). BM and body water compartments were not influenced. These results indicate that during a standardized exercise more ATP is synthesized by the CK reaction when the pre-exercise level in PCr is higher, giving some support to the positive effects recorded on muscle performance.