Fig. 2.
Quantification of voluntary drive. Graphic representation of 2 measures of voluntary drive: the voluntary activation index (VA; A) and the central activation ratio (CAR; B). A maximal stimulus is delivered during a voluntary contraction, and the additional force elicited by the stimulation is referred to as the interpolated twitch, or Tinterp. For the computation of VA, an additional force twitch is elicited by electrical stimulation on the muscle at rest (in the absence of concurrent voluntary contraction) and is referred to as the resting twitch, or Trest. FVOL is the magnitude of the muscle force generated during voluntary contraction. Arrows indicate the time of electrical stimulation.