MUSCLE METABOLISM DURING EXERCISE USING P-31 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY IN ADOLESCENTS

Very little has been reported on muscle energetics during exercise in adolescents. This is attributable to the difficulty of subjecting chil dren to muscle biopsy. The purpose of this study was to investigate th e characteristics of muscle metabolism during exercise in vivo in adol escents by comparing firstly, with adults and secondly, the difference s resulting from physical activity using phosphorus-31 nuclear magneti c resonance ((31)PNMR) spectroscopy. The subjects were boys aged 12 to 15 years, comprising 21 trained boys and 23 control boys, and 6 adult s controls. The ratio of phosphocreatine (PCr):(PCr + P-i), where P-i is inorganic phosphate intracellular pH at exhaustion and the time con stant of PCr during recovery were measured in all the subjects using P -31 NMR. Both groups of children showed higher values of PCr:(PCr + P- i) and intracellular pH at exhaustion than did the adult control group (P < 0.01 or P < 0.05). However, no significant differences were foun d between the trained boys and the control boys with respect to PCr:(P Cr + P-i) and intracellular pH at exhaustion. On the other hand, we fo und the same values for PCr time constant in all groups. This result s uggested no differences of the muscle oxidative capacity between child ren and adults. We concluded that the adolescents, aged 12 to 15 years in both the trained and control groups, had less glycolytic ability d uring exercise than the adults.