Fig. 5.

Force–time histories of cat soleus muscle stretched passively (lowest trace at 6 s), stretched actively (highest trace at 6 s), and activated isometrically at the final stretch length (middle trace at 6 s). Note the increased passive force following muscle deactivation (at 12 s) for the actively stretched muscle, compared to the passively stretched muscle and the muscle activated isometrically at the final stretch length. The increase in passive force following active muscle stretching (here seen at 12 s) was termed passive force enhancement (PFE). Adapted from Herzog and Leonard (2002) with permission