Abstract
Mediolateral stability during walking can be controlled by adjustment of foot placement. Reactive activity of gluteus medius (GM) is modulated during the gait cycle. However, the mechanisms behind the modulation are yet unclear. We measured reactive GM activity and kinematics in response to a mediolateral platform translation during different phases of the gait cycle. Forward simulations of perturbed walking were used to evaluate the isolated effect of the perturbation and the GM response on gait stability. We showed that the potential of GM to adjust lateral foot placement and prevent collisions during swing varies during the gait cycle and explains the observed modulation. The observed increase in stance, swing or combined GM activity causes an outward foot placement and therefore compensates for the loss of stability caused by a perturbation early in the gait cycle. GM activity of the swing leg in response to a platform translation late in the gait cycle counteracts foot placement, but prevents collision of the swing foot with the stance leg. This study provides insights in the neuromechanics of reactive control of gait stability and proposes a novel method to distinguish between the effect of perturbation force and reactive muscle activity on gait stability.
Highlights
Falls in the elderly frequently occur during walking[1], often resulting in significant injuries and loss of independence
An outward strategy, characterized by an increase in stride width, was observed when the platform translation started early in the gait cycle (7.5% and 22.5% gait cycle). For this timing of perturbation, the outward leg is in swing phase and gait stability can be adjusted by outward foot placement (Fig. 2c)
In accordance with previously published results[6], we found that reactive gluteus medius (GM) activity and stepping strategy are modulated during the gait cycle
Summary
Falls in the elderly frequently occur during walking[1], often resulting in significant injuries and loss of independence. Increased activity of the stance and swing leg GM has been observed in response to medio-lateral perturbations during walking[5,6,8]. The above suggests that both stance and swing leg GM muscles contribute to restoring stability after a medio-lateral perturbation during walking and that swing leg GM is important to adjust foot placement. To gain insights into these mechanisms, it is important to unravel the individual contribution of stance and swing leg GM activity to the mechanics of the stepping strategy and to understand the potential of each muscle to influence stepping mechanics during the gait cycle (i.e. potential of the muscle to adjust foot placement and prevention of collision during swing). Correlations between changes in bilateral GM activity and changes in kinematics in response to the perturbation provide limited insight into these underlying mechanisms, because it is hard to separate the individual contribution of the perturbation force (passive response) and the action of individual muscles (active response) in relation to the mechanics and stability of perturbed walking
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