Effect of muscle mass on Vo(2) kinetics at the onset of work

The dependence of O-2 uptake ((V) over dot o(2)) kinetics on the muscle mas s recruited under conditions when fiber and muscle recruitment patterns are similar following the onset of exercise has not been determined. We develo ped a motorized cycle ergometer that facilitated one-leg (1L) cycling in wh ich the electromyographic (EMG) profile of the active muscles was not disce rnibly altered from that during two-leg (2L) cycling. Six subjects performe d 1L and 2L exercise transitions from unloaded cycling to moderate [<ventil atory threshold (VT)] and heavy (>VT) exercise. The 1L condition yielded ki netics that was unchanged from the 2L condition [the phase 2 time constants (tau (1), in s) for <VT were as follows: 1L = 16.8 +/- 8.4 (SD), 2L = 18.4 +/- 8.1, P > 0.05; for >VT: 1L = 26.8 +/- 12.0; 2L = 27.8 +/- 16.1, P > 0. 05]. The overall (V) over dot o(2) kinetics (mean response time) was not si gnificantly different for the two exercise conditions. However, the gain of the fast component (the amplitude/work rate) during the 1L exercise was si gnificantly higher than that for the 2L exercise for both moderate and heav y work rates. The slow-component responses evident for heavy exercise were temporally and quantitatively unaffected by the 1L condition. These data de monstrate that, when leg muscle recruitment patterns are unchanged as asses sed by EMC analysis, on-transient ire, kinetics for both moderate and heavy exercise are not dependent on the muscle mass recruited.