Fig. 9.

Participant force output strategy changes on ramp rise and decline. Left: percent tibialis anterior (%TA) activation (cocontraction) 2.5 s into the ramp contraction reveals 2 distinct force output strategies. Although there is no significant correlation, differences in reference unit firing frequency (ΔF) estimated from motor unit pairs in the top cluster are associated with more TA cocontraction around the time of soleus reference and test unit recruitment. Right: there is no correlation between %TA activation (cocontraction) and ΔF estimates of persistent inward current (PIC) during the descending limb of the ramp, 2.5 s before the contraction ends (left).