The gluteus medius and piriformis muscles have hip extension and
external rotation moment arms throughout the gait cycle [1,2].
Maximum activation peaks were found during the early swing phase as
well as early and late stance. During the latter peak muscle activation
event, the hip was internally rotating via a net hip internal rotation
torque. Thus gluteus medius and piriformis muscle activation was
increased because it was working antagonistically to control the rate or
extent of hip internal rotation.