31P-MRS study of age effects on muscle oxidative capacity

Purpose. -To investigate in vivo comparatively and noninvasively skeletal muscle oxidative capacity from the measurement of PCr resynthesis rates during the post-exercise recovery period in children and adults, using 31-phosphorus magnetic resonance spectroscopy. Method. -Seven prepubertal boys and 10 men performed finger flexions at a frequency of 0.7 Hz against a weight adjusted to 15% of the maximal voluntary contraction for 3 min. Skeletal muscle oxidative capacity was measured during the 15-min post-exercise recovery period from the rate constant of PCr (k(PCr)) time-dependent changes and from the inferred maximum aerobic rate of ATP production (V-max). Results. -End-of-exercise pH was not significantly different between children and adults (6.6 +/- 0.2 versus 6.5 0.2) indicating that indices of PCr recovery kinetics (k(PCr) and V-max) can be reliably compared. The k(PCr) and V-max values were about twofold higher in young boys as compared to men (k(Pcr): 1.7 +/- 1.2 versus 0.7 +/- 0.2 min(-1); V-max: 49.7 +/- 24.6 versus 29.4 +/- 7.9 mM min(-1), P < 0.05). Conclusion. -The results of the present study clearly illustrate a greater mitochondrial oxidative capacity in young children. (C) 2007 Elsevier Masson SAS. Tous droits reserves.