Changes in phosphocreatin concentration of skeletal muscle during intensive intermitted exercise in children and adults

Introduction It was shown that children possess a higher resistance to fatigue and a quicker recovery during high-intensive intermittent exercise compared to adults, which is mainly explained by lower blood lactate concentrations and a more stable blood pH (Falk & Dotan, 2006; Ratel et al., 2006). The aim of the present study was to investigate if this can also be explained by the amount and speed of phosphocreatine (PCr) breakdown and resynthesis during and after intensive short-term anaerobic interval work. Methods 16 untrained children (C; 8 girls, 8 boys: 9.2±0.3 yrs; 139±6 cm; 35.8±7.7 kg body mass; 16.6±2.8 kg muscle mass) and 16 untrained adults (A; 8 women, 8 men: 26.1±0.3 yrs, 175±8 cm, 69.1±9.4 kg body mass, 40.1±8.2 kg muscle mass) participated in the study. All subjects completed an intermittent protocol of dynamic plantar flexion followed by 10 min of passive recovery. The protocol consisted of 10 bouts of 30s exercise (24 concentric and eccentric movements) intermitted by 20s recovery. The individual load corresponded to the 28 repetition maximum. We recorded the absolute and relative changes of PCr during exercise and during post exercise recovery by means of non invasive 31P-magnetic resonance spectroscopy as well as the mean force production. Results The results (mean±SD) were calculated using a multi factor ANOVA (main factors were age, sex and measurement time). No significant differences between the age groups were found for the initial PCr concentrations. Average relative PCr break down during each exercise period was significantly lower (p<0.05) in C (-71.4±5.4%) compared to A (-85.8±4.9%). Time constant to reach 63% of initial PCr during post exercise recovery was significantly shorter in children (C: 47±31s, A: 74±33s, p