Stepping behavior contributes little to balance control against continuous mediolateral trunk perturbations

Abstract

Human bipedal gait is exceptionally stable, but the underlying strategies to maintain stability are unclear, especially in the frontal plane. Our study investigates balance strategies of healthy adults subjected to continuous mediolateral oscillations at the trunk during walking. We used a backpack with a passive inverted pendulum to create perturbations that were fixed, in-phase, or out-of-phase with subjects’ trunk. We evaluated subjects’ corrective strategies and whether they yielded equivalent stability, measured by the margin of stability and the local divergence exponent. The margin of stability measure quantified adjustments in step behavior relative to the centre of mass, and the local divergence exponent measure characterized the chaotic behavior of the system throughout the entire trial. Among the conditions, there was no significant difference in the step width. We found a higher margin of stability for the out-of-phase condition and the lowest local divergence exponent for the in-phase and the highest for the fixed condition. These results indicate that the in-phase condition was more stable with respect to fluctuations throughout gait cycles, and the out-of-phase condition was more stable in terms of foot placement relative to centre of mass. To maintain equivalent or greater gait stability, subjects elected to reduce the motion of their centre of mass rather than alter step width. The reduction in centre of mass motion without reduction in step width suggests direct control of the centre of mass to maintain stability was preferred over adjusting stepping behavior.

Altered active control of step width in response to mediolateral leg perturbations while walking

“…The possible distinction between error-based adaptation and reinforcement learning is currently speculative, and carefully designed future work will be required to differentiate between these mechanisms. Additionally, our finding that perturbations influence the active control of step width may be specific to perturbations that target the legs, as recent work has reported that mediolateral trunk perturbations have a more notable effect on control of the trunk 41 .…”

Perturbations during Gait: A Systematic Review of Methodologies and Outcomes

“…One device applied vibrations to the hip abductor muscles [ 39 ]. One study used an oscillating pendulum system worn on participants’ backs [ 40 ], one study applied a mechanised block to the foot [ 41 ], and one study applied a narrow treadmill-based stepping task while participants were executing a cognitive task [ 42 ].…”

“…Timing of balance perturbation onset : Fourteen studies initiated balance perturbations at heel strike [ 7 , 18 , 19 , 20 , 21 , 22 , 23 , 26 , 27 , 28 , 29 , 35 , 37 , 43 ]. Six studies applied balance perturbations continuously or at intervals during a walking trial [ 8 , 9 , 30 , 31 , 40 , 42 ]. Two studies perturbed participants at toe-off [ 25 , 36 ], one study during mid-stance [ 45 ], one study during single or double support [ 33 ], and one study prior to toe-off [ 44 ].…”

Trunk control during gait: Walking with wide and narrow step widths present distinct challenges

“…The trunk accounts for 48% of the body mass and is the largest contributor to the CoM (MacKinnon and Winter, 1993;Prince et al, 1994). Therefore, how the trunk is controlled will directly influence the CoM, and in some cases adjustment of the CoM motion is preferred over modifying foot placement (Best et al, 2019). The trunk should not be considered a rigid body, since structurally it involves multiple linked segments and degrees of freedom that needs to be fine-tuned.…”