Theodore Towse
Last active: 4/25/2016

Phosphocreatine recovery kinetics following low- and high-intensity exercise in human triceps surae and rat posterior hindlimb muscles.

Forbes SC, Paganini AT, Slade JM, Towse TF, Meyer RA
Am J Physiol Regul Integr Comp Physiol. 2009 296 (1): R161-70

PMID: 18945946 · PMCID: PMC2636983 · DOI:10.1152/ajpregu.90704.2008

Previous studies have suggested the recovery of phosphocreatine (PCr) after exercise is at least second-order in some conditions. Possible explanations for higher-order PCr recovery kinetics include heterogeneity of oxidative capacity among skeletal muscle fibers and ATP production via glycolysis contributing to PCr resynthesis. Ten human subjects (28 +/- 3 yr; mean +/- SE) performed gated plantar flexion exercise bouts consisting of one contraction every 3 s for 90 s (low-intensity) and three contractions every 3 s for 30 s (high-intensity). In a parallel gated study, the sciatic nerve of 15 adult male Sprague-Dawley rats was electrically stimulated at 0.75 Hz for 5.7 min (low intensity) or 5 Hz for 2.1 min (high intensity) to produce isometric contractions of the posterior hindlimb muscles. [(31)P]-MRS was used to measure relative [PCr] changes, and nonnegative least-squares analysis was utilized to resolve the number and magnitude of exponential components of PCr recovery. Following low-intensity exercise, PCr recovered in a monoexponential pattern in humans, but a higher-order pattern was typically observed in rats. Following high-intensity exercise, higher-order PCr recovery kinetics were observed in both humans and rats with an initial fast component (tau < 15 s) resolved in the majority of humans (6/10) and rats (5/8). These findings suggest that heterogeneity of oxidative capacity among skeletal muscle fibers contributes to a higher-order pattern of PCr recovery in rat hindlimb muscles but not in human triceps surae muscles. In addition, the observation of a fast component following high-intensity exercise is consistent with the notion that glycolytic ATP production contributes to PCr resynthesis during the initial stage of recovery.

MeSH Terms (24)

Adenosine Triphosphate Adult Animals Electric Stimulation Exercise Female Glycolysis Hindlimb Humans Hydrogen-Ion Concentration Kinetics Least-Squares Analysis Magnetic Resonance Spectroscopy Male Models, Biological Muscle, Skeletal Muscle Contraction Muscle Fibers, Skeletal Oxidative Phosphorylation Phosphocreatine Phosphorus Isotopes Rats Rats, Sprague-Dawley Sciatic Nerve

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