No / Motion at the midfoot joints can contribute significantly to overall foot motion during gait. However, there is little information regarding the kinematic coupling relationship at the midfoot. The purpose of the present study was to determine whether the coupling relationship at the midfoot and subtalar joints was affected when step width was manipulated during running. Twelve subjects ran over-ground at self-selected speeds using three different step widths (normal, wide, cross-over). Coupling at the midfoot (forefoot relative to rearfoot) and subtalar (rearfoot relative to shank) joints was assessed using cross-correlation techniques. Rearfoot kinematics were significantly different from normal running in cross-over running (P < 0.05) but not in wide running. However, coupling between rearfoot eversion/inversion and shank rotation was consistently high (r > 0.917), regardless of step width. This was also the case for coupling between rearfoot frontal plane motion and forefoot sagittal plane (r < 0.852) and forefoot transverse plane (r > 0.946) motion. There was little evidence of coupling between rearfoot frontal plane motion and forefoot frontal plane motion in any of the conditions. Forefoot frontal plane motion appeared to have little effect on rearfoot frontal plane motion and thus, had no effect on motion at the subtalar joint. The strong coupling of forefoot sagittal and transverse plane motions with rearfoot frontal plane motion suggests that forefoot motion exerts an important influence on subtalar joint kinematics.

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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. / Physical Therapy