Gender differences in onset timing and activation of the muscles of the dominant knee during stair climbing.

An electromyographical analysis (EMG) of knee muscle activation patterns and time delays has rarely been discussed in the literature. The purpose of this study was to compare the activation time and EMG amplitude of the dominant vastus medialis and medial hamstring muscles during stair climbing. Fifteen male and 18 female subjects participated in this study. The subjects were asked to ascend and descend 14 steps, five times. There was a significant time delay difference between genders during stair climbing (F=8.37, p=0.008). The female subjects demonstrated longer time delays while descending the steps. In addition, the female subjects demonstrated significantly lower normalized EMG amplitude during down stair climbing (F=5.77, p=0.025) while the male subjects demonstrated higher normalized EMG amplitude for the vastus medialis muscle while descending the steps. These results suggest that female subjects possess an increased risk factor for knee injuries during down stair climbing due to muscle activation delays with decreased vastus medialis muscle activity.