Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise

• Published in: Journal of applied physiology (1985) 2008-08, Vol.105 (2), p.446-456
• Main Authors: Barker, Alan R, Welsman, Joanne R, Fulford, Jonathan, Welford, Deborah, Armstrong, Neil
• Format: Article
• Language: English
• Subjects: Adenosine Diphosphate - metabolism; Adult; Adults; Bicycling - physiology; Biological and medical sciences; Child; Children & youth; Enzyme kinetics; Enzymes; Exercise - physiology; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Humans; Kinetics; Magnetic Resonance Spectroscopy; Male; Metabolism; Muscle, Skeletal - chemistry; Muscle, Skeletal - metabolism; Oxidation; Oxidative Phosphorylation; Oxygen; Oxygen Consumption - physiology; Phosphocreatine - analysis; Phosphocreatine - metabolism; Sex Characteristics
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00819.2007

1 Children's Health and Exercise Research Centre, University of Exeter, Exeter; 2 Peninsula Medical School, University of Exeter, Exeter; and 3 Cardiff School of Sport, University of Wales Institute, Cardiff, United Kingdom Submitted 31 July 2007 ; accepted in final form 16 May 2008 The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O 2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O 2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the P i /PCr intracellular threshold. The changes in quadriceps [PCr], [P i ], [ADP], and pH were determined every 6 s using 31 P-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 (Q max ) was independent of age and sex (boys, 1.39 ± 0.20 mM/s; girls, 1.32 ± 0.32 mM/s; men, 2.36 ± 1.18 mM/s; women, 1.51 ± 0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O 2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle. 31 P-magnetic resonance spectroscopy; O 2 uptake kinetics; oxidative capacity; maturation Address for reprint requests and other correspondence: N. Armstrong, Children's Health and Exercise Research Centre, St. Luke's Campus Univ. of Exeter, Exeter, EX1 2LU, United Kingdom (e-mail: N.Armstrong{at}exeter.ac.uk )