Reliability of 31P-magnetic resonance spectroscopy during an exhaustive incremental exercise test in children
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This study examined the reliability of 31P-magnetic resonance spectroscopy (MRS) to measure parameters of muscle metabolic function in children. On separate days, 14 children (7 boys and 7 girls) completed three knee-extensor incremental tests to exhaustion inside a whole-body scanner (1.5 T, Phillips). The dynamic changes in the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) and intracellular muscle pH were resolved every 30 s. Using plots of Pi/PCr and pH against power output (W), intracellular thresholds (ITs) for each variable were determined using both subjective and objective procedures. The ITPi/PCr and ITpH were observed subjectively in 93 and 81% of their respective plots, whereas the objective method identified the ITPi/PCr in 88% of the plots. The ITpH was undetectable using the objective method. End exercise (END) ENDPi/PCr, ENDpH, ITPi/PCr and ITpH were examined using typical error statistics expressed as a % coefficient of variation (CV) across all three exercise tests. The CVs for the power output at the subjectively determined ITPi/PCr and ITpH were 10.6 and 10.3%, respectively. Objective identification of the ITPi/PCr had a CV of 16.3%. CVs for ENDpH and ENDPi/PCr were 0.9 and 50.0%, respectively. MRS provides a valuable window into metabolic changes during exercise in children. During knee-extensor exercise to exhaustion, ENDpH and the subjectively determined ITPi/PCr and ITpH demonstrate good reliability and thus stable measures for the future study of developmental metabolism. However, the objectively determined ITPi/PCr and ENDPi/PCr displayed poor reliability.
KeywordsMRS Muscle metabolism Intracellular threshold Developmental
We would like to express our gratitude to the subjects from Wynstream primary school that participated in this study. Furthermore, the technical expertise provided by David Childs in designing the ergometer and analysis software was most appreciated. The study was funded by the Darlington Trust.
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