DISCUSSION:
Over-ground walking demonstrated large sagittal plane hip
motions and joint torques that were greater than transverse plane
motions and joint torques. The hip extensor torques were linked in time
with hip external rotation torques whereas the hip flexor torques were
related to hip internal rotation torques. These results are in agreement
with the general supposition that the hip extensor muscles also produce
hip external rotation; and that the hip flexor muscles also produce hip
internal rotation. However, a closer look at the muscle activation
patterns yields a slightly different interpretation.
The pectineus and iliopsoas muscles have hip flexion and internal
rotation moment arm throughout the gait cycle [1,2]. The pectineus
muscle demonstrated maximum activation peaks during the early swing
phase as well as early and late stance. During the two former peak
pectineus muscle activation events, the hip was externally rotating via a
net hip external rotation torque. Pectineus muscle activation was
increased because it was working antagonistically to control the rate or
extent of hip external rotation. Although slight increases in iliopsoas
muscle activation were noted during early stance and at toe-off, the
activation magnitude remained relatively constant and may indicate that
this muscle did not provide a primary role in producing sagittal or
transverse plane motions of the hip.
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.
The results indicate that the activation of the deep hip muscles
primarily functioned to control or stabilize transverse plane hip rotations
and contributed secondary functions to sagittal plane motion.