It is still unclear how humans control mediolateral (ML) stability in walking and even more so for running. Here, foot placement strategy as a main mechanism to control ML stability was compared between walking and running. Moreover, to verify the role of foot placement as a means to control ML stability in both modes of locomotion, this study investigated the effect of external lateral stabilization on foot placement control. Ten young adults participated in this study. Kinematic data of the trunk (T6) and feet were recorded during walking and running on a treadmill in normal and stabilized conditions. Correlation between ML trunk CoM state and subsequent ML foot placement, step width, and step width variability were assessed. Paired t-tests (either SPM1d or normal) were used to compare aforementioned parameters between normal walking and running. Two-way repeated measures ANOVAs (either SPM1d or normal) were used to test for effects of walking vs. running and of normal vs. stabilized condition. We found a stronger correlation between ML trunk CoM state and ML foot placement and significantly higher step width variability in walking than in running. The correlation between ML trunk CoM state and ML foot placement, step width, and step width variability were significantly decreased by external lateral stabilization in walking and running, and this reduction was stronger in walking than in running. We conclude that ML foot placement is coordinated to ML trunk CoM state to stabilize both walking and running and this coordination is stronger in walking than in running.

It is still unclear how humans control mediolateral (ML) stability in walking and even more so for running. Here, foot placement strategy as a main mechanism to control ML stability was compared between walking and running. Moreover, to verify the role of foot placement as a means to control ML stability in both modes of locomotion, this study investigated the effect of external lateral stabilization on foot placement control. Ten young adults participated in this study. Kinematic data of the trunk (T6) and feet were recorded during walking and running on a treadmill in normal and stabilized conditions. Correlation between ML trunk CoM state and subsequent ML foot placement, step width, and step width variability were assessed. Paired t-tests (either SPM1d or normal) were used to compare aforementioned parameters between normal walking and running. Two-way repeated measures ANOVAs (either SPM1d or normal) were used to test for effects of walking vs. running and of normal vs. stabilized condition. We found a stronger correlation between ML trunk CoM state and ML foot placement and significantly higher step width and step width variability in walking than in running. The correlation between ML trunk CoM state and ML foot placement, step width, and step width variability were significantly decreased by external lateral stabilization in walking and running, and this reduction was stronger in walking than in running. We conclude that ML foot placement is coordinated to ML trunk CoM state to stabilize both walking and running and this coordination is stronger in walking than in running.

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Background:The effect of external lateral stabilization on medio-lateral gait stability has been investigated previously. However, existing lateral stabilization devices not only constrains lateral motions, but also transverse and frontal pelvis rotations. This study aimed to investigate the effect of external lateral stabilization with and without constrained transverse pelvis rotation on mechanical and metabolic gait features. Methods:We undertook 2 experiments with eleven and ten young adult subjects, respectively. Experiment 2 supplemented experiment 1, as it considered several potential confounding factors in the design and set-up of experiment 1. Kinematic, kinetic, and breath-by-breath oxygen consumption data were recorded during 3 walking conditions (normal walking (Normal), lateral stabilization with (Free) and without transverse pelvis rotation (Restricted)) and at 3 speeds (0.83, 1.25, and 1.66 m/s) for each condition.Results: External lateral stabilization significantly reduced the amplitudes of the transverse and frontal pelvis rotations, medio-lateral pelvis displacement, transverse thorax rotation, arm swing, and step width.The amplitudes of free vertical moment, anterior-posterior and vertical pelvis displacements, step length, and energy cost were not significantly influenced by external lateral stabilization. The removal of transverse pelvis rotation restriction by our experimental set-up resulted in significantly higher transverse pelvis rotation, although it remained significantly less than Normal condition. In concert, concomitant gait features such as transverse thorax rotation and arm swing were not significantly influenced by our new set-up. Conclusion:Existing lateral stabilization set-ups not only constrain medio-lateral motions (i.e. mediolateral pelvis displacement), but also constrains other movements such as transverse and frontal pelvis rotations, which leads to several other gait changes such as reduced transverse thorax rotation, and arm swing. Our new setup allowed for more transverse pelvis rotation, however, this did not result in more normal pelvis rotation, arm swing, etc. Hence, to provide medio-lateral support without constraining other gait variables, more elaborate set-ups are needed. Unless such a set-up is realized the observed side effects need to be taken into account when interpreting the effects of lateral stabilization as reported in previous studies.