Résumé
To better understand the mechanisms underlying the pulmonary O2 uptake () slow component during high-intensity exercise, we used 31P magnetic resonance spectroscopy, gas exchange, surface electromyography and near-infrared spectroscopy measurements to examine the potential relationship between the slow components of and phosphocreatine (PCr), muscle recruitment and tissue oxygenation in endurance-trained athletes and sedentary subjects. Specifically, six endurance-trained and seven sedentary subjects performed a dynamic high-intensity exercise protocol during 6 min at an exercise intensity corresponding to 3540% of knee-extensor maximal voluntary contraction. The slow component of (117 +/- 60 ml min-1, i.e. 20 +/- 10% of the total response) was associated with a paradoxical PCr resynthesis in endurance-trained athletes (-0.90 +/- 1.27 mm, i.e. -12 +/- 16% of the total response). Meanwhile, oxygenated haemoglobin increased throughout the second part of exercise and was significantly higher at the end of exercise compared with the value at 120 s (P < 0.05), whereas the integrated EMG was not significantly changed throughout exercise. In sedentary subjects, a slow component was simultaneously observed for and [PCr] time-dependent changes (208 +/- 14 ml min-1, i.e. 38 +/- 18% of the total response, and 1.82 +/- 1.39 mm, i.e. 16 +/- 13% of the total [PCr] response), but the corresponding absolute or relative amplitudes were not correlated. The integrated EMG was significantly increased throughout exercise in sedentary subjects. Taken together, our results challenge the hypothesis of a mechanistic link between [PCr] and slow components and demonstrate that, as a result of a tighter metabolic control and increased O2 availability, the [PCr] slow component can be minimized in endurance-trained athletes while the slow component occurs.