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Muscle [phosphocreatine] dynamics following the onset of exercise in humans: the influence of baseline work-rate

By Andrew M Jones, Daryl P Wilkerson and Jonathan Fulford

Abstract

The kinetics of pulmonary O2 uptake is known to be substantially slower when exercise is initiated from a baseline of lower-intensity exercise rather than from rest. However, it is not known whether putative intracellular regulators of mitochondrial respiration (and in particular the phosphocreatine concentration, [PCr]) show similar non-linearities in their response dynamics. The purpose of this study was therefore to investigate the influence of baseline metabolic rate on muscle [PCr] kinetics (as assessed using 31P-magnetic resonance spectroscopy) following the onset of exercise. Seven male subjects completed ‘step’ tests to heavy-intensity exercise (80% of peak work-rate) from a resting baseline and also from a baseline of moderate-intensity exercise (40% of peak work-rate) using a single-leg knee-extensor ergometer situated inside the bore of a 1.5 T super-conducting magnet. The time constant describing the kinetics of the initial exponential-like fall in [PCr] was significantly different between rest-to-moderate (25 ± 14 s), rest-to-heavy (48 ± 11 s) and moderate-to-heavy exercise (95 ± 40 s) (P < 0.05 for all comparisons). A delayed-onset ‘slow component’ in the [PCr] response was observed in all subjects during rest-to-heavy exercise, but was attenuated in the moderate-to-heavy exercise condition. These data indicate that muscle [PCr] kinetics does not conform to ‘linear, first-order’ behaviour during dynamic exercise, and thus have implications for understanding the regulation of muscle oxidative metabolism

Topics: Skeletal Muscle and Exercise
Publisher: Blackwell Science Inc
OAI identifier: oai:pubmedcentral.nih.gov:2375627
Provided by: PubMed Central
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