Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise

Abstract

The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP], and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age- or sex-related differences were found in the PCr kinetic time constant at the onset (boys, 21+/-4 s; girls, 24+/-5 s; men, 26+/-9 s; women, 24+/-7 s) or offset (boys, 26+/-5 s; girls, 29+/-7 s; men, 23+/-9 s; women 29+/-7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39+/-0.20 mM/s; girls, 1.32+/-0.32 mM/s; men, 2.36+/-1.18 mM/s; women, 1.51+/-0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.

Age‐ and sex‐related differences in muscle phosphocreatine and oxygenation kinetics during high‐intensity exercise in adolescents and adults

“…A PCr slow component was identified in children for the first time, and found to be similar in amplitude to the slow component in adults. Consistent with the findings of Barker et al (12) for moderate-intensity exercise, metabolic control appears to be adult-like in 13 yr old children during high intensity exercise. The kinetics of muscle HHb, measured using NIRS, were significantly faster in children than adults, implying that oxygen delivery is less closely matched to oxygen extraction in children at the onset of exercise.…”

“…A recent 31 P-MRS study by Barker and colleagues (12) has shown that the kinetics of muscle PCr during moderate intensity exercise, i.e. below the inorganic phosphate(P i )/PCr intracellular threshold (IT), are similar between children and adults, implying that the phosphate-linked control of cellular respiration is adult-like in children during moderate intensity exercise.…”

Reproducibility assessment of metabolic variables characterizing muscle energetics in Vivo: A 31P‐MRS study

“…A few studies have recently reported 31 P MRS results recorded during repeated square-wave exercises (9,26,27). This procedure was used in order to improve the reliability of metabolic measurements and is actually similar to what is commonly performed for the V O 2p kinetics response (28), which exhibits inherent irregularities in gas exchange due to breath by breath fluctuations.…”

Can we simply infer mitochondrial function from PCr resynthesis after exercise in skeletal muscle?

“…On that basis, the initial rate of PCr recovery and the maximum aerobic capacity should be considered as additional indexes to compare the post-exercise PCr recovery rate and mitochondrial oxidative capacity across different populations when end-of-exercise pH and PCr concentration values are different or not taken into account. This was the case in some previously published studies that investigated in vivo mitochondrial function from childhood to young and/or late adulthood (5,6). In contrast, this was not the case in other studies that investigated age-related changes in mitochondrial oxidative capacity from childhood to adulthood (7) and examined the association between mitochondrial alterations and insulin sensitivity in overweight and normal-weight children (8).…”