The effect of decreased muscle energy stores on the$\dot V_{O_2 }$ kinetics at the onset of exercisekinetics at the onset of exercise

Summary

The kinetics of adjustment of oxygen uptake$(\dot V_{O_2 } )$ 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$\dot V_{O_2 }$ on-response ($t_{\tfrac{1}{2}} \dot V_{O_2 }$ 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$\dot V_{O_2 }$ and lactic acid accumulation in blood (Δ[la_b]) during the$\dot V_{O_2 }$ transient were measured. Preceding the 75 W_A by 5 min of 125 W leg exercise decreased significantly the$t_{\tfrac{1}{2}} \dot V_{O_2 }$ 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$t_{\tfrac{1}{2}} \dot V_{O_2 }$ 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$t_{\tfrac{1}{2}} \dot V_{O_2 }$ on- (20% and 50%, respectively). The Δ[la_b] increased linearly with$t_{\tfrac{1}{2}} \dot V_{O_2 }$ 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$\dot V_{O_2 }$ to exercise.