Symmetrical and asymmetrical hip rotation and its relationship to hip rotator muscle strength

BackgroundJoint motion studies suggest that adults have symmetrical hip rotation range of motion. Asymmetries in hip rotation are often related to lower extremity musculoskeletal conditions. The purpose of this study was to determine if muscle strength differences occur in subjects with symmetrical vs. asymmetrical hip rotation. We hypothesize that those with asymmetrical hip rotation will have less strength in the standard 0° test position when compared to a position where the joint is in its center or mid-position.MethodsSixty-four subjects participated. Muscle strength was measured in the standard 0° and mid-range hip positions. Subjects were divided into three groups depending on hip rotation, symmetrical, internal rotation greater than external rotation and external rotation greater than internal rotation. Data were analyzed using a 3 (Classification Group: Symmetrical vs. greater external rotation vs. greater internal rotation) × 2 (Muscle: External Rotator vs. Internal Rotator) × 2 (Position: Standard 0° vs. Center or Off-mid) ANOVA with the last two factors treated as repeated measures.FindingsMeasures of left and right side yielded significant effects for Muscle, Classification Group × Muscle, Classification Group × Position, Muscle Group × Position, and Classification Group × Muscle × Position.InterpretationThe results suggest that difference in muscle strength of the hip rotators is dependent upon the position that the hip rotator muscle is tested and the type of hip rotation symmetry or asymmetry present. Before muscle testing or strengthening the hip rotator muscles the presence of joint rotation asymmetries and the effect of joint positioning must be considered.