Figure 9.

LL responses with the adapted muscle preinhibited are sensitive to the direction of the training load. A, Brachioradialis stretch responses evoked by elbow extensor perturbations. Left, Mean perturbation-evoked activity of the preinhibited brachioradialis muscle for mechanical perturbations that extended the elbow. Vertical dashed lines demarcate the time epochs used to characterize muscle feedback responses. Horizontal axis is the time relative to perturbation onset (t = 0 ms; solid vertical line). Shaded regions indicate the SEM with black and red shading corresponding to brachioradialis activity in the baseline and adaptation phases, respectively. Right, Binned analysis of brachioradialis stretch responses for perturbations that extended the elbow. B, Stretch responses for the preloaded triceps lateral muscle evoked by elbow extensor perturbations. Left, Mean perturbation-evoked activity of the triceps lateral muscle for extensor perturbations. Data are plotted in the same format and color scheme as in A. Right, Binned analysis of triceps lateral stretch responses for perturbations that extended the elbow. C, Brachioradialis stretch responses evoked by elbow flexor perturbations. Left, Mean perturbation-evoked activity of the brachioradialis muscle for perturbations that flexed the elbow. D, Triceps lateral stretch responses evoked by perturbations that flexed the elbow. Left, Mean perturbation-evoked activity of the triceps lateral muscle. Right, Binned analysis of triceps lateral responses. Data are plotted in the same format and color scheme as panel A. *p < 0.05, **P < 0.01, ***p < 0.001.