Physiologic response to endurance work as a function of prior exercise.

Five male subjects performed an endurance task (ET) following 20 min of prior exercise (PE) at work loads corresponding to approximately 30%, 45%, 60% and 75% of VO2 max. There was a 1-min rest interval between the PE and ET. The ET consisted of 10 min of walking at a speed and slope corresponding to 75% of VO2 max after which time the speed was increased by 10 m/min each minute until the subject could no longer continue. Although endurance performance was not significantly influenced by the PE-30 and PE-45, performance following PE-60 and PE-75 was significantly impaired, as was the peak VO2 attained at the end of the ET. Although O2 deficits at the beginning of the ET were reduced by the higher intensities of PE, the plasma lactate levels at the 8th min of the ET were not significantly lower under those conditions since those levels of PE led to some lactate accumulation during the PE itself. VO2 during the last 5 min of the constant load part of the ET was similar in all conditions but PE-75, during which it was higher. It is suggested that although PE might be useful for tasks in which the initial work loads are maximal or supramaximal with respect to VO2, it is of questionable value in endurance tasks that begin at a high but submaximal intensity.