Submitted on July 31, 2007
Accepted on May 16, 2008
Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate intensity exercise
Alan Robert Barker1, Joanne R Welsman1, Jonathan Fulford2, Deborah Welford3, and Neil Armstrong1*
1 Children's Health and Exercise Research Centre, University of Exeter, Exeter, Devon, United Kingdom
2 Peninsula Medical School, University of Exeter, Exeter, Devon, United Kingdom
3 Cardiff School of Sport, University of Wales Institute Cardiff, Cardiff, United Kingdom
* To whom correspondence should be addressed. E-mail: n.armstrong{at}exeter.ac.uk.
The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization (mVO2) during a 'step' change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared to adults both at the onset and offset of moderate intensity exercise, in concert with the previous demonstration of faster phase II VO2 kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeat constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP] and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age or sex related differences were found in the PCr kinetic time constant at the onset (boys, 21 ± 4 s; girls, 24 ± 5 s; men, 26 ± 9 s; women, 24 ± 7 s) or offset (boys, 26 ± 5 s; girls, 29 ± 7 s; men, 23 ± 9 s; women 29 ± 7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39 ± 0.20; girls, 1.32 ± 0.32; men, 2.36 ± 1.18, women, 1.51 ± 0.53 mM·s-1). These results are consistent with the notion that the putative phosphate linked regulation of mVO2 is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.
