Center of mass velocity based predictions in balance recovery following pelvis perturbations during human walking

Abstract

In many simple walking models, foot placement dictates the center of pressure location and ground reaction force components, whereas humans can modulate these aspects after foot contact. Because of the differences, it is unclear to what extent predictions made by models are valid for human walking. Yet, both model simulations and human experimental data have previously indicated that the center of mass (COM) velocity plays an important role in regulating stable walking. Here, perturbed human walking was studied to determine the relationship of the horizontal COM velocity at heel strike and toe-off with the foot placement location relative to the COM, the forthcoming center of pressure location relative to the COM, and the ground reaction forces. Ten healthy subjects received mediolateral and anteroposterior pelvis perturbations of various magnitudes at toe-off, during 0.63 and 1.25 m s −1 treadmill walking. At heel strike after the perturbation, recovery from mediolateral perturbations involved mediolateral foot placement adjustments proportional to the mediolateral COM velocity. In contrast, for anteroposterior perturbations, no significant anteroposterior foot placement adjustment occurred at this heel strike. However, in both directions the COM velocity at heel strike related linearly to the center of pressure location at the subsequent toe-off. This relationship was affected by the walking speed and was, for the slow speed, in line with a COM velocity-based control strategy previously applied by others in a linear inverted pendulum model. Finally, changes in gait phase durations suggest that the timing of actions could play an important role during the perturbation recovery.

The recovery response to a novel unannounced laboratory-induced slip: The “first trial effect” in older adults

“…Once an unintended perturbation occurs, foot placement is even more critical in restoring stability. Vlutters et al (2016) found that recovery from medial-lateral perturbations on treadmill walking involved medial-lateral foot placement adjustments proportional to the medial-lateral COM velocity. Hof (2008) reported that changes in foot placement were associated with stability after perturbations in walking.…”

Novel methodology for assessing total recovery time in response to unexpected perturbations while walking

“…Recently, Madehkhaksar et al [10] found that in order to increase dynamic stability immediately after perturbation, young adults walk with shorter, wider strides and a higher cadence, with a stronger response to medio-lateral than to anterior-posterior perturbations. Vlutters et al [14] found similar results when applying perturbations to the hip during walking stating that "at heel strike after the perturbation, recovery from medio-lateral perturbations involved medio-lateral foot placement adjustments proportional to the medio-lateral center of mass velocity. In contrast, for anteroposterior perturbations, no significant anteroposterior foot placement adjustment occurred".…”

The effect of anteroposterior perturbations on the control of the center of mass during treadmill walking

“…The most extensively studied mechanism to stabilize gait is foot placement (Bauby and Kuo, 2000, 51 Townsend, 1985, Wang and Srinivasan, 2014, Vlutters et al, 2016. Foot placement is considered the main 52 mechanism for stabilizing gait in the AP movement direction (but also in mediolateral (ML) direction) 53 (MacKinnon and Winter, 1993, Patla, 2003.…”

“…A second mechanism is to apply active muscle moments 54 around the ankle of the stance foot ('ankle strategy') (Horak and Nashner, 1986). Experimental data showed 55 that humans adjust sagittal plane muscle moments around the ankle of the stance foot following AP 56 mechanical perturbations of gait (Vlutters et al, 2016) (but also frontal plane muscle moments following 57 ML perturbations (Hof and Duysens, 2018)). These ankle moments are reflected in a shift of the center of 58 pressure of the ground reaction force (CoP).…”