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Walking humans respond to pulls or pushes on their upper body by changing where they place their foot on the next step. Usually, they place their foot further along the direction of the upper body perturbation. Here, we examine how this foot placement response is affected by the average step width during walking. We performed experiments with humans walking on a treadmill, both normally and at five different prescribed step widths. We prescribed step widths by requiring subjects to step on lines drawn on the treadmill belt. We inferred a linear model between the torso marker state at mid-stance and the next foot position. The coefficients in this linear model (which are analogous to feedback gains for foot placement) changed with increasing step width as follows. The sideways foot placement response to a given sideways torso deviation decreased. The fore–aft foot placement response to a given fore–aft torso deviation also decreased. Coupling between fore–aft foot placement and sideways torso deviations increased. These changes in foot placement feedback gains did not significantly affect walking stability as quantified by Floquet multipliers (which estimate how quickly the system corrects a small perturbation), despite increasing foot placement variance and upper body motion variance (kinematic variability).

Postoperative gait mechanics in persons with femoroacetabular impingement syndrome (FAIS) remain understudied as a treatment outcome despite observed, yet inconclusive, preoperative gait abnormalities. Females with FAIS demonstrate worse preoperative patient-reported hip function and altered hip mechanics when compared with males; it is unknown whether these sex differences persist postarthroscopy. The purpose of this study was to compare sex-specific gait kinematics between persons at least 1 year postarthroscopy for FAIS and healthy comparisons. General linear models with estimating equations were used to evaluate the effect of (a) limb and sex within each group, and (b) limb and group within each sex for peak sagittal and frontal plane trunk, pelvis, and hip kinematics during stance phase of gait. Analyses were covaried by gait speed. Seventeen females and eight males an average 2.5 years postarthroscopy (1.1-7.2 year) for FAIS were compared with healthy females (n = 7) and males (n = 5). Females in the FAIS group presented with an average of 4.6°more anterior pelvic tilt, and 4.8°less hip extension compared with healthy females (P ≤ .03) and 8.6°less trunk flexion, 4.8°more anterior pelvic tilt, 3.1°more pelvic drop, and 7.5°more hip flexion than males with FAIS (P ≤ .03). Males in the FAIS group presented with 2.9°less pelvic drop, and 3.2°less hip adduction than healthy males. Preoperative gait mechanics were not collected and thus changes in mechanics could not be evaluated. This study is significant to clinicians who treat patients postarthroscopy to consider sex-specific gait impairments.

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