Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 88, Issue 4, Pages 1181-1191Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/jappl.2000.88.4.1181
Keywords
nuclear magnetic resonance; oxidative phosphorylation; skeletal muscle; phosphocreatine; inorganic phosphate
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The purpose of this study was to examine with P-31-magnetic resonance spectroscopy energy metabolism during repeated planter flexion isometric exercise (Ex-1-Ex-4) at 32 +/- I and 79 +/- 4% of maximal voluntary contraction (MVC) before and during a creatine (Cr) feeding period of 5 g/day for 11 days. Eight trained male subjects participated in the study. ATP was unchanged with Cr supplementation at rest and during exercise at both intensities. Resting muscle phosphocreatine (PCr) increased (P < 0.05) from 18.3 +/- 0.9 (before) to 19.6 +/- 1.0 mmol/kg wet wt after 9 days. At 79% MVC, PCr used, Pi accumulated, and pH at the end of Ex-1-Ex-4 were similar after 4 and II days of Cr supplementation. In contrast, PCr utilization and Pi accumulation were lower and pH was higher for exercise at 32% MVC with Cr supplementation, suggesting aerobic resynthesis of PCr was more rapid during exercise. These results suggest that elevating muscle Cr enhances oxidative phosphorylation during mild isometric exercise, where it is expected that oxygen delivery matches demands and predominantly slow-twitch motor units are recruited.
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