Hip External Rotator Strength and Compensatory Movement in Three Different Positions

Abstract

Measuring intrinsic hip external rotator strength (ER) without compensatory pelvic motion and activation of the sartorius is important for preventing or rehabilitating lower extremity injuries. However, the optimal method for measuring intrinsic hip ER muscle strength while minimizing compensatory pelvic motions and activation of the sartorius is unclear. The purpose of this study is to compare measurements of hip ER strength, compensatory pelvic motion, and sartorius activation in the sitting, prone, and sidelying positions. Thirty-one healthy subjects (16 males and 15 females) were recruited for this study. Hip ER strength, pelvic kinematics, and sartorius muscle activation were measured during maximal isometric contraction of the hip ER in the sitting, prone, and sidelying positions. Hip ER strength was measured using a load-cell-type strength-measurement sensor. Pelvic kinematics was measured using an electromagnetic motion-tracking sensor. Electromyography was used to measure sartorius muscle activity. Data were analyzed using one-way repeated-measures analysis of variance. The result showed that hip ER strength and sartorius muscle activation were significantly lower in the sidelying compared with the sitting and prone positions (p < 0.01). Pelvic anteroposterior tilting was significantly greater in the sitting compared with the prone and sidelying positions (p < 0.01). Pelvic rotation differed significantly among positions (p < 0.01). Pelvic lateral tilting was significantly greater in the prone compared with the sitting position (p < 0.017). Compensatory pelvic motion and sartorius muscle activation were lower when hip ER strength measurements were made in the sidelying position. Therefore, the sidelying position is effective for measuring selective intrinsic hip ER strength.