Changes in phosphocreatine concentration of skeletal muscle during high-intensity intermittent exercise in children and adults

Purpose The aim of the present study was to test the hypotheses that a greater oxidative capacity in children results in a lower phosphocreatine (PCr) depletion, a faster PCr resynthesis and a lower muscle acidification during high-intensity intermittent exercise compared to adults. Methods Sixteen children (9.4 +/- 0.5 years) and 16 adults (26.1 +/- 0.3 years) completed a protocol consisting of a dynamic plantar flexion (10 bouts of 30-s exercise at 25 % of one repetition maximum separated by 20-s recovery), followed by 10 min of passive recovery. Changes of PCr, ATP, inorganic phosphate, and phosphomonoesters were measured by means of 31 Phosphorous-magnetic resonance spectroscopy during and post-exercise. Results Average PCr (percentage of [PCr] at initial rest (%[PCr](i))) at the end of the exercise (adults 17 +/- 12 %[PCr](i), children 38 +/- 17 %[PCr](i), P < 0.01) and recovery periods (adults 37 +/- 14 %[PCr](i), children 57 +/- 17 %[PCr](i), P < 0.01) was significantly lower in adults compared to children, induced by a stronger PCr decrease during the first exercise interval (adults -73 +/- 10 %[PCr](i), children-55 +/- 15 %[PCr](i), P < 0.01). End-exercise pH was significantly higher in children compared to adults (children 6.90 + 0.20, -0.14; adults 6.67 + 0.23, -0.15, P < 0.05). Conclusions From our results we suggest relatively higher rates of oxidative ATP formation in children's muscle for covering the ATP demand of high-intensity intermittent exercise compared to adults, enabling children to begin each exercise interval with significantly higher PCr concentrations and leading to an overall lower muscle acidification.