Bilateralism of EMG profiles in human locomotion

In gait studies, minor importance has been generally given to the aspect of symmetry. Consequently, an unstated assumption has been that the right and left legs present symmetrical outcomes. The purpose of the present study was to verify this assumption throughout the use of electromyographic (EMG) profiles of activity from the two legs during gait. Eight subjects participated in the study. Two muscles, the soleus and rectus femoris, were recorded from both legs using surface electrodes. Foot switches placed under each heel served to indicate the gait cycles (N = 10) that were recorded per subject. The EMG signal was transformed into a linear envelope through full-wave rectification and filtering using second order low-pass filters (6 Hz). These envelopes were transformed in amplitude in percent of a maximum voluntary contraction (% MVC). These were digitized (50 Hz) and the sample points used to perform regression analyses contrasting left and right (homologus) muscles. Coefficients of correlation between the EMG linear envelopes of the homologous muscles showed high correlations and thus nearly identical shape. However important differences in EMG amplitude between the legs were found. Implications of these findings for future research in gait are discussed.