The effect of decreased muscle energy stores on the {Mathematical expression} kinetics at the onset of exercisekinetics at the onset of exercise

The kinetics of adjustment of oxygen uptake {Mathematical expression} 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 (∼P) stores, by blood flow occlusion (BFO) and/or preceding exercise, on the half time of the {Mathematical expression} on-response ( {Mathematical expression} on-) during arm exercise. Twelve male subjects performed an arm exercise test at a standard intensity of 75 W (75 W_A) following six procedures designed progressively to decrease O₂ and/or ∼P stores. Breath-by-breath {Mathematical expression} and lactic acid accumulation in blood (Δ[la_b]) during the {Mathematical expression} transient were measured. Preceding the 75 W_A by 5 min of 125 W leg exercise decreased significantly the {Mathematical expression} on- (63-47 s). Preceding the 75 W_A with either arm BFO and isometric exercise (1 min), no-load or 25 W (25 W_A) arm cranking (5 min) did not significantly affect {Mathematical expression} on- or Δ[la_b]. Preceding 75 W_A with 5-10 min BFO or BFO plus 25 W_A resulted in a significant decrease in {Mathematical expression} on- (20% and 50%, respectively). The Δ[la_b] increased linearly with {Mathematical expression} on-responses greater than 24 s. These data suggest that the local depletion of O₂ and/or ∼P stores play an important role in determining the kinetics of adjustment of {Mathematical expression} to exercise.