Tisserand, R. | Search bioRxiv

bioRxiv2024

Harmonization of Margin of Stability Calculations and Investigation of the Impact of Foot Length, Foot Width, Gait Speed, and Body Mass

The margin of stability (MoS), the minimum distance between the extrapolated center of mass and the edges of the base of support (BoS), is one of the most widely used metric to describe the mechanical stability during gait. In the current literature, the markers used to define the edges of the BoS are variable and the MoS model neglects the influence of anthropometric factors, such as foot length, foot width, and body mass. This study aimed to evaluate differences between anteroposterior (AP) and mediolateral (ML) MoS measures using various BoS edge definitions (AP: n = 3 methods, ML: n = 4 methods) and to investigate the impact of foot length, foot width, gait speed, and body mass on the MoS measures. Results show that the BoS edges definition affects the resulting MoS across the entire stance phase (AP: p<0.001 between the 3 methods; ML: p<0.001 between the 4 methods). Moreover, the AP MoS is influenced by foot length (p<0.029), as well as gait speed and body mass on both the AP (gait speed: p<0.001; body mass: p<0.038) and ML (gait speed: p<0.032; body mass: p<0.001) MoS. This study proposes a new approach based on optimal foot markers for defining the edges of the BoS, which may contribute to better assess mechanical stability during gait. Finally, the results suggest that normalizing the MoS (i.e., the AP MoS by foot length, gait speed, and body mass, and the ML MoS by gait speed and body mass) can facilitate comparisons between populations.

bioengineering↗

bioRxiv2018

Anticipatory adjustments of posture allow elderly fallers to achieve a balance recovery performance equivalent to elderly non-fallers

BackgroundIn an important number of laboratory-based perturbation experiments, differences in the balance recovery performance of elderly fallers and non-fallers are moderate or absent. This performance may be affected by the subjects adjusting their initial posture in anticipation of the perturbation.\n\nResearch questionsDo elderly fallers and non-fallers adjust their posture in anticipation of externally-imposed perturbations in a laboratory setting, and how does this impact their balance recovery performance?\n\nMethods21 elderly non-fallers, 18 age-matched elderly fallers and 11 young adults performed both a forward waist-pull perturbation task and a Choice Stepping Reaction Time (CSRT) task. Whole-body kinematics and ground reaction forces were recorded. For each group, we evaluated the balance recovery performance in the perturbation task, change in initial center of mass (CoM) position between the CSRT and the perturbation task, and the influence of initial CoM position on task performance.\n\nResultsThe balance recovery performance of elderly fallers was equivalent to elderly non-fallers (p > 0.5 Kolmogorov-Smirnov test). All subject groups anticipated forward perturbations by shifting their CoM backward compared to the CSRT task (young: 2.1% of lower limb length, elderly non-fallers: 2.7%, elderly fallers: 2.2%, Hodges-Lehmann estimator, p < 0.001 Mann-Whitney U). This backward shift increases the probability of resisting the traction without taking a step.\n\nSignificanceThe ability to anticipate perturbations is preserved in elderly fallers and may explain their preserved balance recovery performance in laboratory-based perturbation tasks. Therefore, future studies aimed at predicting fall risk in elderly adults should carefully control for this postural strategy, by interleaving perturbations of different directions for example.

neuroscience↗