An Electromyographic Study of Hip Muscle Activity in Varying Subtalar Joint Positions: Implications for Anterior Cruciate Ligament Injury Risk

Purpose: The purpose of this study is to determine if subtalar joint position affects the activity of hip musculature in static standing, and by those results imply a correlation between foot position and ACL injury risk. Methods: Thirty participants took part in this randomized study in which EMG data were collected during 3 trials of 3 subtalar joint positions on the right lower extremity. Subtalar joint positions included a flat surface to represent a neutral subtalar position, a 5-degree incline rising from lateral to medial, promoting a supinated attitude of the foot, and the third position was on a 5- degree incline rising from medial to lateral promoting a pronated attitude of the foot. EMG activity was monitored in the gluteus maximus, gluteus medius, rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius during static standing. Results: All 30 subjects were tested individually and able to complete all of the trials required for data collection. Repeated analysis of variance (AN OVA) was utilized in each of the six muscle groups tested within the three different subtalar conditions. There was no significant difference found in the EMG activity of gluteus maximus, gluteus medius, biceps femoris, rectus femoris, and gastrocnemius. There was a significant difference found in the EMG activity of the tibialis anterior muscle demonstrating a higher EMG activity in subtalar flat and pronated positions as compared to the subtalar supination position. The EMG results from subject 12 had an unusually high amount of interference in the muscle activity of the rectus femoris and tibialis anterior. For this reason, readings in all three conditions for rectus femoris and tibialis anterior were discarded for subject 12. Conclusion: There was no significant difference found in hip muscle activity with varying subtalar joint positions. Even though our results showed no significant differences, future studies including more functional positions and kinetics throughout the lower extremity might produce results that demonstrate a relationship between the two areas and, therefore, possibly identify this relationship as a determinant for anterior cruciate ligament injury risk