Effect of Creatine Supplementation on Pcr Repletion

The purpose of this study was to test the effect of creatine supplementation on muscle [PCr] and on its repletion kinetics after exercise. Sixteen male subjects were divided into two groups in a double blind fashion. They were instructed to consume over 13 days, either creatine (3 × 7 g a day), or an equivalent amount of placebo. The [PCr] was measured in the calf muscle by 31P NMRS, the day before the beginning of the treatment and the day following its completion. During the same session, the half-repletion time (T1/2) was measured by means of an exercise performed in the magnet. The exercise consisted in 50 plantar fexions-extensions over a period of 1 min against a load equal to 70% of MVC. A spectrum was acquired every 15 s during the exercise and during 5 min of recovery. T1/2 was calculated by means of the fitting of an exponential function through the [PCr] measured during the recovery. The results showed that muscle [PCr] at rest increased from 18.7 ± 22.1 mmol.kg-1 to 22.4 ± 1.56 mmol.kg-1 after a period of creatine supplementation (P=0.002) whereas it remained unchanged in the placebo group. [Pi] and muscle pH were not influenced by exogenous creatine. After exercise, T1/2 was not either modified (34.6 ± 5.0 s versus 40.0 ± 13.0 s) by creatine supplementation. To conclude, faster [PCr] repletion does not appear to explain the effects of creatine supplementation observed during intermittent exercises.