EFFECTS OF SHORT-TERM TRAINING ON KINETICS OF CARDIORESPIRATORY RESPONSES AND SKELETAL MUSCLE OXYGENATION

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59 To determine whether the acceleration of the kinetics of oxygen uptake (VO2) by endurance training result from a central circulatory adaptation or an improvement in oxygen extraction by skeletal muscle, VO2 kinetics, heart rate (HR), and skeletal muscle oxygenation by NIRS in response to step changes in work rate were measured during the course of a 6-week training. Fourteen untrained male subjects performed training involving 30 min cycle exercise repeated 3 days/week at either 80% or 120% intensity of pretraining ventilatory threshold (VT). Data across three repetitions on each week were averaged, and the O2 deficit, HR deficit, and accumulated change in deoxy [Hb] were determined. The O2 and HR deficits for the 120% VT training group decreased significantly following training, while these parameters were almost unchanged for 80% VT training group. The accumulated change in deoxy [Hb] also gradually decreased with the training week for 120% VT training group, indicating the improvement in the peripheral circulation. The relative decrease in O2 deficit correlated well with both the HR deficit and accumulated change in deoxy [Hb] for 120% VT training group. These results indicate that: (1) exercise training at an intensity above VT is effective in improving exercise capacity with reductions of O2 and HR deficits and decrease in the accumulated change in deoxy [Hb], and (2) the reduction of O2 deficit (improvement of VO2 kinetics) appears to be associated with both the central and peripheral circulatory adaptations.