The Effects of Fatigue on Pathomechanics and Electromyography in Female Runners with Iliotibial Band Syndrome

Abstract

The etiology of iliotibial band syndrome (ITBS) is not fully understood, however, dysfunction at the hip and decreased resistance to fatigue have been suggested to contribute to development of the syndrome. The objective of this study was to investigate differences in hip abductor strength and fatigue resistance, hip muscle activation timing and hip joint kinematic, kinetic and joint coupling patterns in female runners with and without ITBS. In addition, this study examined the effects of a run to exertion on these variables. Twelve female runners with ITBS and 20 healthy female runners participated in this study. Gluteus medius strength and electromyographic (EMG) data were collected during isometric testing. In addition, EMG data from the gluteus medius and tensor fascia latae muscles as well as 3-dimensional kinematic, kinetic and joint coupling data were collected during overground running. All data were collected prior-to and following a run to exertion. Prior to the run to exertion, with runners in a "fresh" state, there were no differences in hip abductor strength, kinematic joint coupling and terminal swing phase muscle activation timing between runners with ITBS and healthy runners. In a "fresh" state, ITBS runners demonstrated less resistance to fatigue at their gluteus medius muscle than did the healthy runners. As a result of exertion, runners with ITBS demonstrated decreased peak hip adduction angles during the stance phase of running gait. There were no group-by-exertion interactions for peak hip internal rotation angles, hip abductor and external rotator moments, kinematic joint coupling or hip abductor strength. There was a main effect of exertion for hip abductor moments, hip external rotator moments and hip abductor strength whereby both healthy and injured runners demonstrated 3.8, 4.2 and 7.3% decreases respectively following the run to exertion. In addition, there was a main effect of exertion on hip frontal/knee transverse plane kinematic joint coupling during the first half of loading where runners demonstrated a 7.3% increase in joint coupling values following the run to exertion. Our data did not detect group-by-exertion interactions or main effects of group or exertion with respect to terminal swing muscle activation timing. There was a significant group-by-exertion interaction when examining fatigue resistance. In a fresh-state, runners with ITBS demonstrated less resistance to fatigue than their healthy counterparts. Following the run to exertion, these differences did not exist. The results of this study suggest that currently symptomatic runners with ITBS demonstrate a potentially compensatory pattern of decreased stance phase hip adduction as compared with healthy runners. Hip internal rotation, abductor moments, external rotator moments or kinematic joint coupling do not appear to discriminate between the two groups. The results of this study also suggest that hip abductor strength may not be as large of a factor in the development of ITBS as previously thought. Instead, this muscle's endurance, or its ability to resist fatigue may play a larger role.