Figure 4. The effect of voluntary contraction on the dynamic index in twenty-one muscle spindle afferents.

The change in dynamic index was calculated as the difference between the dynamic index in trials in the relaxed muscle and that during voluntary contraction at 6 (A) and 12 % MVT (B). The change in dynamic index is plotted against the increase in firing rate during the static phase of stretch. Each point in these plots represents an individual afferent: ○, primary afferents (n=17); □, secondary afferents (n=4). The afferents from Figs 2 and 3 are indicated (A-D).