Factors affecting premature plantarflexor muscle activity during hemiparetic gait

In hemiparetic stroke survivors, premature plantarflexor muscle activity (PPF) often appears as a gait abnormality from terminal swing to the loading response on the paretic side. This study aimed to discern factors giving rise to PPF. Lower extremity function, spasticity magnitude, and gait electromyograms were assessed in 31 hemiparetic stroke survivors. Mean amplitudes during gait phases were determined for the paretic soleus, tibialis anterior, rectus femoris, and biceps femoris. The subjects were classified into PPF and non-PPF groups based on their relative soleus amplitude at different phases of gait, and group differences in each measurement were calculated and subjected to logistic regression. The PPF group showed less activity of the tibialis anterior during the swing phase but greater activity of the rectus femoris during the swing phase and of the biceps femoris, both prematurely and during the loading response. Logistic regression revealed premature activity of the biceps femoris to be a significant variable related to presence of PPF (odds ratio = 1.054). PPF in hemiparetic gait may work with the biceps femoris to supplement compromised lower extremity extension strength. PPF might be reduced by attaining enhanced strength of the hip and knee extensors at the time of initial contact during gait.