Pelvic and femoral contributions to bilateral hip flexion by subjects suspended from a bar

Objective. To quantify the contribution of the pelvis and femur to active bilateral hip flexion conducted while subjects are suspended by their hands from a bar. Design. Descriptive and experimental. Background. Voluntary hip flexion while in a suspended position is used in abdominal strengthening regimens and is required for certain athletic activities. The degree to which pelvic rotation contributes to this maneuver has not been established. Methods. Pelvic and femoral motions were documented in 14 subjects who performed bilateral hip flexion while they hung by their hands from a bar. A supporting board as well as the trunk, pelvis and thigh were marked with reflective spheres; motion of the pelvis and thigh relative to the board was captured by video analysis. Ratios of pelvic to femoral motion were calculated and the influence of hamstring length (78° of straight leg raising) and knee position (flexed vs extended) on the ratio was determined. Results. The mean pelvifemoral ratio ranged from 0.131 to 0.355, depending on hamstring length and knee position. Pelvic rotation therefore contributed a mean 13.1–35.5% of the observed hip flexion. A 2 × 2 mixed-model analysis of variance showed that the ratio was influenced significantly by each of these two independent variables. The largest pelvic contribution occurred during hip flexion with the knee in the extended position among subjects with shorter hamstrings. Conclusions. Pelvic motion is an integral part of hip flexion conducted while subjects are suspended their hands from a bar. The pelvic contribution depends on knee position and hamstring length. Relevance During suspended activities involving hip flexion (e.g. gymnastics), pelvic rotation plays an integral role throughout the range. Inherent or imposed differences in hamstring length can alter the contribution of the pelvis to the motion. Hip flexion, therefore, might be influenced by conditions affecting the ability of the pelvis to rotate (e.g. spinal fusion), or the femur to move on the pelvis (e.g. degenerative joint disease), or be altered by hamstring tension.