Comparison of the effects of the knee flexion and extension during side-lying hip abduction on the activity and onset time of the gluteus medius and quadratus lumborum

Abstract

BACKGROUND: An increase in the compensatory action of the quadratus lumborum (QL) during side-lying hip abduction (SHA) can lead to lateral movement impairment of the pelvis. OBJECTIVE: To compare the effects of knee flexion (KF) and knee extension (KE) during SHA at abduction angles of 25∘, 35∘, and 45∘ on the activity and onset time of the gluteus medius (GM) and QL. METHODS: Thirty healthy men were recruited and randomly divided into two groups: those with SHA with KF and those with SHA with KE. The subjects performed SHA at three angles of abduction in a random order. Surface electromyography was used to record the muscle activities of the GM and QL. RESULTS: The QL activity decreased significantly more in the KE group than in the KF group at each of the three angles of abduction during SHA. The GM/QL activity ratio increased significantly in the KE compared to the KF group. In addition, in the KE group, the onset of the GM activity was significantly earlier than that of the QL activity. On the other hand, in the KF group, the onset of the GM activity occurred later than that of the QL activity. CONCLUSIONS: These findings indicate that KE is more effective than KF in selectively activating the GM during SHA by reducing the QL activity and firing the GM earlier than the QL.