Fig. 1. Full-wave-rectified normalised electromyographic (EMG) recordings of major leg muscles during one cycle of walking and running at selected speeds of a typical subject. Speed is given as a percentage of the preferred gait transition speed. One vertical scale division in all plots corresponds to 100% of the corresponding peak of the EMG envelope in maximum isometric contraction; one horizontal scale division in all plots corresponds to 200ms. EMG activity was shifted to the right along the time axis by 40ms to account for the electromechanical delay between muscle activation and joint moments. Vertical lines separate the stance phase (on the left of the line) from the swing phase (on the right of the line). EMG activity of the ankle extensors (SO and GA), knee extensor (VA) and hip extensor (GLM) whose activation was primarily associated with the stance phase has positive values. EMG activity in the ankle flexor (TA), knee flexor (BFL) and hip flexor (RF) whose activation was primarily associated with the swing phase is inverted. SO, soleus; GA, gastrocnemius medialis; VA, vastus medialis; GLM, gluteus maximus; TA, tibialis anterior; BFL; long head of biceps femoris; RF, rectus femoris.