The influence of net ground reaction force orientation on mediolateral stability during walking

Previous work has linked the eccentricity of the net ground reaction force (GRF_net) to increased mediolateral instability during single-step voluntary and compensatory stepping responses. The present work sought to understand the extent to which such control mechanisms for mediolateral stability are present during gait.

How do gait velocity and step width constraints influence the kinetic control of mediolateral stability control among healthy participants?

25 participants performed three walking conditions - normal walking with self-selected speed and foot-placement, fast walking with self-selected foot-placement, and narrowbase walking - across a 10-meter walkway. Lateral instability was quantified by the mediolateral margin of stability (MoS_ML). The frontal-plane eccentricity of the GRF_net was calculated as the difference between GRF_net vector orientation and that of a line joining the coordinates of COP_net and COM. Two discrete time-points (P1 and P2) following foot-contact were examined, as they have been suggested to be indicative of proactive and reactive COM control, respectively. Task-related differences in the magnitude and timing of kinematic and kinetic outcome variables were analysed using one-way ANOVAs with repeated-measures.

With constraints on step-width in narrow-base walking, participants exhibited reduced stability as evidenced by reduced MoS_ML, alongside reductions in the peak GRF_net eccentricity (θ_d) at P1. Participants exhibited no reduction in stability during fast walking, as revealed by the MoS_ML in part because of a similar onset of P1 within the gait cycle. P2 magnitude was larger in narrow-base walking relative to fast-walking, and occurred at an earlier point in the gait cycle.

Findings suggest proactive mechanisms (i.e. P1) may predominantly regulate mediolateral stability during walking. Reactive mechanisms (i.e. P2), however, may be capable of offsetting instability in situations where proactive mechanisms are insufficient.