Figure 1.

Example co-contraction metrics. (A) Eight gait events dividing the gait cycle into seven phases: loading response (LR), mid-stance (MSt), terminal stance (TSt), pre-swing (PSw), initial swing (ISw), mid-swing (MSw), and terminal swing (TSw). Illustrated immediately below, is example EMG in the medial gastrocnemius (MG, solid) and tibialis anterior (TA, dotted) for a healthy control (left) and an individual post-stroke (right). The shaded area reflects the area under the lower trace at any point, used as the antagonist in the traditional co-contraction index calculations. (B) Illustration using the same example EMG as above, however the shaded area reflects the area under the muscle that should be the antagonist within each phase. PSw is not shaded because the antagonist muscle typically switches between MG and TA in this phase. (C) The resulting wasted contraction for the same subjects, the lower of the two traces (wide dashes), and the effective contraction, which is calculated as the higher trace minus the lower trace (narrow dashes). The wasted contraction index is the mean of the wasted contraction, expressed as a percentage of the maximum effective contraction.