Recruitment and Activity of the Pectineus and Piriformis Muscles During Hip Rehabilitation Exercises An Electromyography Study

Background: The pectineus muscle has been reported to function primarily as a hip flexor and secondarily as a hip internal rotator; the piriformis muscle has been reported to function as an abductor and external rotator of the hip. The recruitment and activations of these muscles during hip rehabilitation exercises have not been detailed. Hypothesis: The authors hypothesized that they would measure the highest pectineus activation during exercises involving hip flexion, with moderate pectineus activation during exercises with hip internal rotation. They also hypothesized that they would measure the highest piriformis activation during exercises involving hip abduction and/or external rotation. Study Design: Descriptive laboratory study. Methods: Ten healthy volunteers completed 13 hip rehabilitation exercises with electromyography (EMG) electrodes inserted under ultrasound guidance into the pectineus and piriformis muscle bellies. The EMG signals were recorded and exercise activation levels were reported as a percentage of a maximum voluntary contraction (MVC). Results: Both the highest peak pectineus activation (62.8% +/- 26.6% MVC) and the highest mean pectineus activation (33.1% +/- 17.4% MVC) were measured during the supine hip flexion exercise. Moderate activation was found during the single- and double-legged bridge and both phases of the stool hip rotation exercise. The highest peak piriformis activation was observed in the single-legged bridge (MVC, 35.7% +/- 25.7%), and the highest mean piriformis activation was observed in the prone heel squeeze (MVC, 24.3% +/- 8.2%). Similar moderate activation levels were found for single-legged hip abduction and resisted hip extension. Conclusion: The pectineus was highly activated during hip flexion exercises and moderately activated during exercises requiring rotational hip stabilization in either direction, rather than with internal hip rotation only. The piriformis was most activated during static external rotation and abduction while the participants' hips were in slight extension. These observations indicate that the pectineus and piriformis are both muscles that contribute to hip stabilization.