Fig. 7. Peak instantaneous muscle power produced per unit muscle mass increased with increasing acceleration (A). The power averaged over the entire stance period, the mean stroke power, increased with increasing acceleration (B). Muscle-mass-specific powers were calculated by assuming that all hindlimb extensors contributed to the power applied to the center of mass. Linear regressions (N=49) are shown for peak power output (y=64.7x+87.5, r²=0.84, P<0.01) and mean stroke power (y=30.8x-1.1, r²=0.93, P<0.01).