Muscle [phosphocreatine] dynamics following the onset of exercise in humans: the influence of baseline work-rate.
The kinetics of pulmonary O(2) 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 (31)P-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.
School of Sport and Health Sciences, St Luke's Campus, University of Exeter, Heavitree Road, Exeter EX1 2LU, UK. a.m.jones@exeter.ac.uk
Andrew M
AM
Jones
Daryl P
DP
Wilkerson
Jonathan
J
Fulford
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D019069:Cell Respiration / Q000502:physiology; D016552:Ergometry; D015444:Exercise / Q000502:physiology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D010725:Phosphocreatine / Q000378:metabolism*; D005082:Physical Exertion / Q000502:physiology*
D010725:Phosphocreatine; D000255:Adenosine Triphosphate