Effects of prior exercise on oxygen uptake and phosphocreatine kinetics during high-intensity knee-extension exercise in humans

摘要

class="enumerated" style="list-style-type:decimal">A prior bout of high-intensity square-wave exercise can increase the temporal adaptation of pulmonary oxygen uptake () to a subsequent bout of high-intensity exercise. The mechanisms controlling this adaptation, however, are poorly understood.We therefore determined the dynamics of intramuscular [phosphocreatine] ([PCr]) simultaneously with those of in seven males who performed two consecutive bouts of high-intensity square-wave, knee-extensor exercise in the prone position for 6 min with a 6 min rest interval. A magnetic resonance spectroscopy (MRS) transmit-receive surface coil under the quadriceps muscle allowed estimation of [PCr]; was measured breath-by-breath using a custom-designed turbine and a mass spectrometer system.The kinetics of the second exercise bout were altered compared with the first such that (a) not only was the instantaneous rate of change (at a given level of ) greater but the phase II τ was also reduced – averaging 46.6 ± 6.0 s (bout 1) and 40.7 ± 8.4 s (bout 2) (mean ± s.d.) and (b) the magnitude of the later slow component was reduced.This was associated with a reduction of, on average, 16.1 % in the total exercise-induced [PCr] decrement over the 6 min of the exercise, of which 4.0 % was due to a reduction in the slow component of [PCr]. There was no discernable alteration in the initial rate of [PCr] change. The prior exercise, therefore, changed the multi-compartment behaviour towards that of functionally first-order dynamics.These observations demonstrate that the responses relative to the work rate input for high-intensity exercise are non-linear, as are, it appears, the putative phosphate-linked controllers for which [PCr] serves as a surrogate.