Tensor fascia latae and gluteal muscles myoelectric responses to increasing levels of hip medial rotation torque

Medial hip rotation is typically attributed to the tensor fascia latae (TFL) and lateral rotation, to the gluteus maximus. However, experimental studies in cadavers suggest that the TFL lacks a moment arm for medial rotation and that the gluteus maximus may act as hip medial rotator depending on the hip flexion angle. In order to address this contradictory thinking, we measured the myoelectric activity of TFL, gluteus medius and gluteus maximus (superior portion, GMaxS, and inferior portion, GMaxI) for increasing levels of medial rotation torque applied to the hip. To keep frontal and sagittal plane hip joint net torques constant during the experiments, the medial hip rotation torque was changed by displacing standard weights along an aluminum bar device, thereby producing pure medial hip rotation torques. The effect of increasing medial hip rotation torque was investigated for a fully extended hip (0 degrees), and at 45 degrees and 90 degrees of flexion. We found an increase in the myoelectric activity of the TFL (similar to 90%up arrow, p = 0.002) at 90 degrees of flexion and of the GMaxS (similar to 7%up arrow, p = 0.048) at the extended position with an increase in medial hip torque application (from 0 to 7.4 N.m.). For the GMed (regardless of hip position) and for the 45 degrees position (regardless of muscle), no systematic changes across torque conditions were observed. In contrast to the common clinical assumption and current practice thinking, our results indicate that an increase in TFL activity is required to control for an increase in external torque towards hip medial rotation.

Automated summary

This study examined the effects of medial hip rotation torque on the myoelectric activity of the tensor fascia latae (TFL), gluteus medius, and gluteus maximus. The results showed that there was a significant increase in TFL and superior portion of the gluteus maximus activity during medial hip rotation at 90 degrees of hip flexion.