Linking whole-body angular momentum and step placement during perturbed human walking

Abstract

Human locomotion is remarkably robust to environmental disturbances. Previous studies have thoroughly investigated how perturbations influence body dynamics and what recovery strategies are used to regain balance. Fewer studies have attempted to establish formal links between balance and the recovery strategies that are executed to regain stability. We hypothesized that there would be a strong relationship between magnitude of imbalance and recovery strategy during perturbed walking. To test this hypothesis, we applied transient ground surface translations that varied in magnitude, direction, and onset time while eight healthy participants walked on a treadmill. We measured stability using integrated whole-body angular momentum (iWBAM) and recovery strategy using step placement. We found the strongest relationships between iWBAM and step placement in the frontal plane for earlier perturbation onset times in the perturbed step (R2=0.52, 0.50) and later perturbation onset times in the recovery step (R2=0.18, 0.25), while correlations were very weak in the sagittal plane (all R2 <= 0.13). These findings suggest that iWBAM influences step placement, particularly in the frontal plane, and that this influence is sensitive to perturbation onset time. Lastly, this investigation is accompanied by an open-source data set to facilitate research on balance and recovery strategies in response to multifactorial ground surface perturbations, including 96 perturbation conditions spanning all combinations of three magnitudes, eight directions, and four gait cycle onset times.

Consequences of changing planned foot placement on balance control and forward progress

“…To determine the change in iWBAM (ΔiWBAM) between uninhibited and inhibited trials for each participant we calculated the mean and standard deviation of iWBAM for each uninhibited condition. For each inhibited trial, the trial iWBAM was subtracted from the mean iWBAM of the corresponding uninhibited condition then divided by the standard deviation of iWBAM from the corresponding uninhibited condition [32]. The resulting value is the trial-level change in iWBAM between the uninhibited and inhibited trials, in units of standard deviations from the uninhibited condition mean.…”

“…The integral of WBAM (iWBAM) over the course of a step represents the total rotation of the body with respect to the gait cycle (i.e. total pitch, roll, or yaw over the course of a step) [32,40]. iWBAM was integrated after time-normalization and is with respect to the step cycle.…”

“…Humans tightly regulate WBAM to stay upright when walking [30,31]. Further, perturbations that impact frontal-plane WBAM, but not sagittal-plane WBAM, influence the placement of subsequent steps [32]. This association between WBAM and foot placement in the frontal plane is likely a necessary action to limit instability [32].…”

“…Further, perturbations that impact frontal-plane WBAM, but not sagittal-plane WBAM, influence the placement of subsequent steps [32]. This association between WBAM and foot placement in the frontal plane is likely a necessary action to limit instability [32]. In the case of an inhibited step, a sudden change to foot placement would likely disrupt anticipated trajectory and WBAM.…”

Effect of hip abduction assistance on metabolic cost and balance during human walking

“…Dynamic gait balance is typically controlled by adjusting foot placement (22,36,37) or changing the step width or cadence (22,(38)(39)(40). Changes in balance are represented as changes in the margin of stability (MoS) (36), variability in the center of pressure (CoP) (41), or changes in whole-body angular momentum (42)(43)(44). We measured the indicators related to dynamic gait balance, such as the lateral MoS, average step width and variability, stride length, cadence, and variability of the CoP.…”