Functional roles of the calf and vastus muscles in locomotion.

Simultaneous and synchronized electromyography and cinematography were used to record the co-ordination of calf and vastus muscle activity with the angular motions of the segments and joints of the lower limb in two female and three male subjects, while each performed one complete series of tests in which they walked at 2.5, 3.2 and 4.2 mph on a treadmill, which was level, or held at upward tilts of 5 and 10 degrees. The raw EMG recordings were also integrated into uniform pulses, which were electronically counted in 5 second time blocks for each of the walking conditions tested. The objectives of this study were to: 1) quantitatively measure the relative increases of EMG activity in thses two groups of muscles under the various degrees of stress, which resulted from walking at increased speeds and degrees of upward tilt, and 2) correlate these gross quantitative relationships of activity with the patterns of co-ordination found between these two groups of muscles under the corresponding stressed conditions of walking. The results of this study indicate that although with increases of speed and upward tilt the absolute values of integrated EMG increased more for the calf than for the vastus muscles, the relative increases of EMG were consistently greater for the vasti, which reached their peak intensity of activity at moments during the walking stride, when their knee extending action stretched the gastrocnemius heads across the back of the knee joint, and thereby assisted the calf muscles lift the heel, and plantar flex the ankle joint--the most essential actions for producing the push-off and thrust in the normal walking stride.