HIP ABDUCTOR MUSCLE FORCE; AN EXPERIMENTAL STUDY OF THE INFLUENCE OF HIP POSITION WITH PARTICULAR REFERENCE TO ROTATION.

1. A dried, male pelvis articulated with the lower two lumbar vertebrae and femur were positioned to represent the situation present when a man is standing on one extremity. The abductor muscles (gluteus minimus, gluteus medius, and tensor fasciae latae, and iliotibial tract) were represented by chains and load cells designed to incorporate SR-4 strain gauges. 2. The model was loaded at the approximate center of gravity of the body with different weights and different hip positions to determine the counterforce on the load cells and thereby an approximation of the force exerted by the abductor muscles of the hip under the conditions tested. 3. The results by this method agreed within 4 per cent with the theoretical values calculated from a roentgenogram of the same model. 4. On the model the total abductor muscle force for a 150-pound man was found to be 154 pounds. 5. Superincumbent body weight should be used for all calculations rather than total body weight. 6. Abductor-muscle force is least with the pelvis in abduction and most with the pelvis in adduction. 7. Rotation of the femur internally or externally from its anatomical or neutral position necessitates increased abductor-muscle force to maintain a level pelvis. 8. The theory that abnormal gait patterns associated with rotational deformities of the femur represent the most efficient use of the hip abductor mechanism was supported by the findings.