Co-Activation of Leg Muscles Differs While Ascending and Descending Stairs

Abstract

Co-activation of the agonist-antagonist leg muscles has been studied during walking on flat, uphill, and downhill surfaces. This study aimed to examine any plausible difference between the amount of co-activation of the leg muscles while ascending and descending stairs. Twelve healthy individuals (20-32y, 9 males) went up 12 stairs one at a time, and then down one at a time. Surface electrodes were placed on tibialis anterior and gastrocnemius muscles of the subjects' left leg, and electromyography (EMG) signals were amplified within 15-250 Hz, and recorded at 1 kHz sampling rate. The signals were segmented to each step’s data; the root-mean-square (RMS) values of each segment were calculated over 100 ms windows with 50% overlap between successive windows. The baseline activity, defined as the averaged RMS value over 500 ms before stepping forward, was subtracted from the recorded data. Then, the signal of each segment was normalized by the maximum value during the cycle. Co-activation, defined as the overlapped area between RMS value of the EMG signals of the agonist and antagonist muscles, was calculated for every ascending and descending step and averaged for all ascending (and descending) steps for each subject. Results showed co-activation during ascending stairs was significantly (p<0.01) larger than that of during descending.