P-31-MAGNETIC RESONANCE SPECTROSCOPY OF LEG MUSCLE METABOLISM DURING EXERCISE IN CHILDREN AND ADULTS

Gas exchange response to high-intensity exercise differs in children and adults. We hypothesized that these findings are related to a lower anerobic ATP supply in children. We predicted therefore a maturation of muscle high-energy phosphate metabolism during exercise. To test this hypothesis, we measured calf muscle P(i), phosphocreatine (PCr), and pH with P-31-nuclear magnetic resonance spectroscopy during rest and progressive exercise in 10 children and 8 adults. No differences were found at rest in pH and P(i)/PCr between children and adults. Exercise resulted in a greater increase in P(i)/PCr (P < 0.001) and decrease in pH (P < 0.0001) in adults than in children. Six adults and five children exhibited a transition from a slow to a faster rate of P(i)/PCr increase and pH decrease during exercise. No significant differences were found between the two groups in the initial slow-phase slopes of P(i)/PCr and pH as a function of work rate. In contrast, during the fast phase, P(i)/PCr increased (slope: adults 23.6 +/- 9.8, children 10.7 +/- 2.5; P < 0.05) and pH decreased (slope: adults -6.0 +/- 1.9, children -3.7 +/- 1.2; P < 0.05) more rapidly in adults than in children. In conclusion, high-intensity exercise results in different kinetics of P(i)/PCr and pH between children and adults. These results suggest that children are less able than adults to affect ATP rephosphorylation by anaerobic metabolic pathways during high-intensity exercise.