The effect of decreased muscle energy stores on the VO2 kinetics at the onset of exercise.

The kinetics of adjustment of oxygen uptake (VO2) at the onset of a square wave of exercise in man has been shown to be variable and related mainly to factors located distal to the capillary. The present study examined the effects of decreasing oxygen and high energy phosphates (approximately P) stores, by blood flow occlusion (BFO) and/or preceding exercise, on the half time of the VO2 on-response (t1/2 VO2 on-) during arm exercise. Twelve male subjects performed an arm exercise test at a standard intensity of 75 W (75 WA) following six procedures designed progressively to decrease O2 and/or approximately P stores. Breath-by-breath VO2 and lactic acid accumulation in blood (delta [1ab]) during the VO2 transient were measured. Preceding the 75 WA by 5 min of 125 W leg exercise decreased significantly the t1/2 VO2 on- (63-47 s). Preceding the 75 WA with either arm BFO and isometric exercise (1 min), no-load or 25 W (25WA) arm cranking (5 min) did not significantly affect t1/2 VO2 on- or delta [1ab]. Preceding 75 WA with 5-10 min BFO or BFO plus 25 WA resulted in a significant decrease in t1/2 VO2 on- (20% and 50%, respectively). The delta [1ab] increased linearly with t1/2 VO2 on-responses greater than 24 s. These data suggest that the local depletion of O2 and/or approximately P stores play an important role in determining the kinetics of adjustment of VO2 to exercise.