The effects of unexpected mechanical perturbations during treadmill walking on spatiotemporal gait parameters, and the dynamic stability measures by which to quantify postural response

Abstract

Most falls occur after a loss of balance following an unexpected perturbation such as a slip or a trip. Greater understanding of how humans control and maintain stability during perturbed walking may help to develop appropriate fall prevention programs. The aim of this study was to examine changes in spatiotemporal gait and stability parameters in response to sudden mechanical perturbations in medio-lateral (ML) and anterior-posterior (AP) direction during treadmill walking. Moreover, we aimed to evaluate which parameters are most representative to quantify postural recovery responses. Ten healthy adults (mean = 26.4, SD = 4.1 years) walked on a treadmill that provided unexpected discrete ML and AP surface horizontal perturbations. Participants walked under no perturbation (normal walking), and under left, right, forward, and backward sudden mechanical perturbation conditions. Gait parameters were computed including stride length (SL), step width (SW), and cadence, as well as dynamic stability in AP- (MoS-AP) and ML- (MoS-ML) directions. Gait and stability parameters were quantified by means, variability, and extreme values. Overall, participants walked with a shorter stride length, a wider step width, and a higher cadence during perturbed walking, but despite this, the effect of perturbations on means of SW and MoS-ML was not statistically significant. These effects were found to be significantly greater when the perturbations were applied toward the ML-direction. Variabilities, as well as extremes of gait-related parameters, showed strong responses to the perturbations. The higher variability as a response to perturbations might be an indicator of instability and fall risk, on the same note, an adaptation strategy and beneficial to recover balance. Parameters identified in this study may represent useful indicators of locomotor adaptation to successfully compensate sudden mechanical perturbation during walking. The potential association of the extracted parameters with fall risk needs to be determined in fall-prone populations.

Characteristics of First Recovery Step Response following Unexpected Loss of Balance during Walking: A Dynamic Approach

“…Since the CoM velocity is closely related to the perturbation magnitudes, this suggests that, in regard to step length, our participants demonstrated more flexible behavior. In their review, Brujin and van Dieën [39] showed a large body of evidence suggesting that lateral recovery stepping is regulated based on the CoM state in the preceding swing phase, i.e., foot placement adjustments post perturbation were correlated with CoM velocity [29,38,52,53], and that compensatory step adjustments were actively generated [20]. For example, it was found that in mechanical perturbations in the mediolateral direction during walking, a larger lateral foot placement was associated with gluteus medius activity during the swing phase and the mediolateral movement of the CoM [38].…”

“…These data suggest that commonly occurring, clinically important falls Gerontology 2020;66:362-370 DOI: 10.1159/000505649 related to walking are unexpected, and may have greater injury potential in a lateral direction. While most research on balance reactive control has focused on perturbations during standing [7,9,10], there is now a large body of literature on reactive balance to perturbations during walking specifically in response to anterior-posterior perturbations [11][12][13][14][15][16][17][18][19][20][21][22]. Less data exist evaluating responses to lateral loss of balance while walking.…”

Identifying differences in gait adaptability across various speeds using movement synergy analysis

“…Nonetheless among healthy adults, both high-and low-variability can be associated with gait stability indicating that other factors may also be at play in producing instable gait (Beauchet et al, 2009). Variability and changes in variability may also reflect the adaptability of gait and its adaptions to environmental demands (Madehkhaksar et al, 2018). Therefore, the context and subject in question must be considered when assessing movement from this perspective.…”

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

“…Of several previous studies examining the kinematic properties of balance recovery [8][9][10], some have demonstrated that the stabilization of walking speed and stepping frequency following perturbation is a two-stage process [[11] [12]. The first stage (initial response) is aimed at reducing the perturbation effect to minimum, the second stage is a gradual return to steady state.…”

“…Hof and colleagues have proposed that accurate generation of step length and step width will optimize the required timing and placement of the extrapolated center of mass within the base of support [8,9]. 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.…”