The Contribution of the Rectus Femoris to Hip Flexion

The Contribution of the Rectus Femoris to Hip Flexion

The rectus femoris is a bi-articular muscle, which crosses the hip and knee joints. Its’ actions at the knee are well documented and have been known since the early 1900s. The work of the rectus femoris at the hip has received less attention and the extent to which it flexes the hip is uncertain. Detailed information regarding rectus femoris actions at the hip could have considerable benefits. Strength and fitness trainers could find the information useful in designing workout regimens, and clinicians would benefit when planning rehabilitation programs, particularly with patients displaying pelvic tilt issues. Therefore, this study investigated the influence of selected combinations of knee and hip joint angles on
the hip flexor function of the rectus femoris. Methods: The rectus femoris of 16 subjects was stimulated via surface electrodes across 16 knee and hip joint combinations. The isometric torque produced before, during and after each of three stimulations at each joint combination was recorded with an Isokinetic dynamometer. Results: The knee joint angle significantly influenced the rectus femoris’ hip flexion moments of force. The effect was linear with a greater flexion moment of force arising as the knee angle moved from 0 to 90 degrees. The hip flexion force was greatest with the knee joint flexed to 90 degrees across all hip joint angles. The mean hip flexion moment of force for 0 and 30 degree knee angles was 10.90 (+5.1) Nm, increasing to 13.87 (+5.5) Nm for the 60 and 90 degree knee angles. Conclusion: The 60 and 90 degrees of knee flexion produced the longest rectus femoris length and the greatest hip flexion moments of force for this muscle. The angle of the hip did not significantly increase the hip flexion moments of force for the rectus femoris during stimulation, but became a significant factor when the stimulation was absent.