Figure 2. Ramp stretch reflex muscle activity and platform movement analyses.

Soleus waveform averages (A) were used to establish analysis windows and significant points, such as SLR onset, peak and end, as well as MLR onset and end. A mean + 3 SD baseline threshold was established from a 100 ms period ending 10 ms before platform onset (dashed horizontal line) and was used to determine SLR onset (dashed vertical line). The peak of the SLR waveform (solid vertical line) was calculated from a fixed window (35–55 ms after platform onset). In some cases, the SLR did not return to baseline before MLR onset. In these cases, the lowest value of either the baseline mean + 3 SD, 25% SLR peak or 50% SLR peak reached in soleus rectified EMG before 65 ms post‐platform onset (continuous for 3 ms; 50% SLR peak in A) was used to define the end of the SLR (dashed vertical line). SLR onset and end were confirmed by visual inspection and SLR peak amplitude and latency were re‐calculated within the SLR window. MLR peak was calculated in a window spanning 5 ms after SLR end to 150 ms after platform onset. The MLR analysis window began (dashed vertical line) at the lowest point between SLR end and MLR peak and adjusted manually if necessary (adjusted here). MLR end (dashed vertical line) was defined as the point where the MLR dropped below the highest of either 25% MLR peak (solid horizontal line) or the baseline mean + 3 SD threshold used to determine SLR onset. SLR and MLR analysis windows were created for both LOW and HIGH trials and the earliest onsets and latest ends were used to set common analysis windows; analysis windows differed across participants. Peak platform movement parameters for SLR–specific velocity profiles (B) were referenced to the time of SLR peak amplitude (solid vertical line) by subtracting SLR onset latency from the latency of SLR peak. As shown with representative data, the SLR response increased with faster stretch speeds (C).