Anticipatory control of human gait following simulated slip exposure

Abstract

Rob den otter & claudine J. c. Lamoth A cautious gait (cG), marked by wider and shorter steps, is typically employed to mitigate expected perturbations proactively. However, it is not well understood if and how cG is informed by the task requirements. therefore, we assessed how cG is adjusted to these requirements. three groups of ten healthy young adults were exposed to a single uninterrupted protocol of treadmill walking that consisted of three distinct phases. Spatiotemporal step characteristics and margins of stability of the unperturbed strides were compared when participants were (i) only warned of a perturbation, (ii) exposed to fifty unilateral (right) slip-like perturbations and (iii) kept unaware of perturbation removal. Only the perturbation intensity predictability differed between groups. This was either kept consistent or pseudo-randomly or randomly varied. Participants walked with wider and shorter steps following the perturbation warning. However, this extinguished in continuing perturbation absence. next, during perturbation exposure, participants shortened the step of the perturbed but increased the step of the unperturbed leg. This did not differ between groups. Finally, participants persisted in displaying CG on perturbation removal, but this extinguished over time. collectively, we show that cG is functionally adjusted to the task requirements. These findings may have practical implications for fall-prevention training. Bipedal gait is a challenging activity, considering that the vertical projection of the centre of mass (CoM) is outside the base of support (BoS) for approximately 80% of the gait cycle 1. In fact, walking involves continuous falling motions, which are caught by a relocation of the BoS during every step. Nevertheless, walking is generally stable and adaptive, as healthy adults are able to adjust their gait continuously to accommodate environmental and task demands 2. However, walking in an environment encountering unpredictable or changing events becomes particularly challenging when the walking performance declines due to natural ageing or pathology 3. As a result, older adults often employ a cautious gait (CG) strategy to safeguard against potential balance loss 4,5. Although this form of anticipatory control has been described as a generic strategy that is characterized by wider and shorter steps 6 , it is not well understood if and how CG is informed by the requirements of the task. The present study addressed how anticipatory control of gait is adjusted to accommodate these requirements. Anticipatory control relies on sensory input and provides the means to identify and proactively accommodate environmental challenges instantaneously 2. Walking on ice is a simple illustration of this, which is typically characterized by wider and shorter steps. These cautious adjustments safeguard dynamic balance and can reduce the need for time-critical, reactive control 7. Putatively, people employ a CG by the necessity of uncertainty (i.e. where, when, and if a perturbation will occur)...

Lower extremity joint compensatory effects during the first recovery step following slipping and stumbling perturbations in young and older subjects

“…When a perturbation occurs, the cerebral cortex instinctively responds by adopting more cautious gait to position the body for stability [ 41 ]. Generally such gait alterations are referred to as gait placement strategies [ 17 , 18 ].These deliberate modifications protect the dynamic stability and can lessen the requirement for time-critical, reactive control [ 9 , 42 ]. As such, it is frequently employed by older adults [ 43 ].…”

“…Gait pattern alterations are typically characterized and quantified in terms of spatiotemporal parameters [ 44 ]. To proactively reduce anticipated disturbances, wider and shorter steps are regularly applied, which likewise works for unanticipated ones [ 42 ].Wider steps taken voluntarily help improve immediate lateral stability [ 45 ], and shorter step length can lead to an increase in the medio-lateral and backward MoS against anterior–posterior slip [ 46 , 47 ]. These observable stepping strategies are an important contribution to fall prevention [ 46 ].…”

“…Expected and unanticipated perturbations can produce inconsistent effects. Studies showed that human, however, subconsciously reduce step length when subjected to warning perturbations [ 42 , 47 ], which is a sign of “caution” [ 45 ]. Moreover, a recent study concluded that the changing gait patterns caused adjustments in Stance/Swing ratio, thus shortening the stance time, which was also considered to be one of the main strategies for recovery after backward slipping perturbation [ 50 ].…”

Recovery of dynamic stability during slips unaffected by arm swing in people with Parkinson’s Disease

“…In addition, it has been shown that after perturbation exposure, healthy adults adopt a more cautious gait i.e. with shorter, wider, and slower steps as a means to enhance their dynamic stability to prevent potential future perturbations [ 10 , 22 ]. It is possible that our participants used a similar strategy when walking after initial slip exposure.…”

“…Meanwhile, in the unperturbed (recovery) limb, the hip and knee extend to bring the leg that is entering the swing phase rapidly to the ground to increase the base of support (BOS) [ 16 ]. After slip exposure, individuals walk with a “cautious gait” strategy where step time and width are increased, and step length is reduced [ 20 , 22 , 23 ]. This is accompanied by a shift in the dynamical state (position and velocity) of their COM anteriorly and away from the mediolateral edges of their base of support at heel-strike [ 10 , 18 , 20 ].…”