Abstract
The aim of this investigation was to examine the adaptation of the muscle phosphates (e.g. phosphocreatine (PCr) and ADP) implicated in regulating oxidative phosphorylation, and oxygenation at the onset of high intensity exercise in children and adults. The hypotheses were threefold: primary PCr kinetics would be faster in children than adults; the amplitude of the PCr slow component would be attenuated in children; and the amplitude of the deoxyhaemoglobin/myoglobin (HHb) slow component would be reduced in children. Eleven children (5 girls, 6 boys, 13βΒ±β1 years) and 11 adults (5 women, 6 men, 24βΒ±β4 years) completed two to four constant work rate exercise tests within a 1.5 T MR scanner. Quadriceps muscle energetics during high intensity exercise were monitored using ^31^PβMRS. Muscle oxygenation was monitored using nearβinfrared spectroscopy. The time constant for the PCr response was not significantly different in boys (31βΒ±β10βs), girls (31βΒ±β10βs), men (44βΒ±β20βs) or women (29βΒ±β14βs, main effects: age, pβ=β0.37, sex, pβ=β0.25). The amplitude of the PCr slow component relative to endβexercise PCr was not significantly different between children (23βΒ±β23%) and adults (17βΒ±β13%, pβ=β0.47). Endβexercise [PCr] was significantly lower, and [ADP] higher, in females (18βΒ±β4βmM and 53βΒ±β16βΒ΅M) than males (23βΒ±β4βmM, pβ=β0.02 and 37βΒ±β11βΒ΅M, pβ=β0.02), but did not differ with age ([PCr]: pβ=β0.96, [ADP]: pβ=β0.72). The mean response time for muscle tissue deoxygenation was significantly faster in children (22βΒ±β4βs) than adults (27βΒ±β7βs, pβ=β0.01). The results of this study show that the control of oxidative metabolism at the onset of high intensity exercise is adultβlike in 13βyearβold children, but that matching of oxygen delivery to extraction is more precise in adults. Copyright Β© 2010 John Wiley & Sons, Ltd.