Use of the extended feasible stability region for assessing stability of perturbed walking.

Walking stability has been assessed through gait variability or existing biomechanical measures. However, such measures are unable to quantify the instantaneous risk of loss-of-balance as a function of gait parameters, body sway, and physiological and perturbation conditions. This study aimed to introduce and evaluate novel biomechanical measures for loss-of-balance under various perturbed walking conditions. We introduced the concept of 'Extended Feasible Stability Region (ExFSR)' that characterizes walking stability for the duration of an entire step. We proposed novel stability measures based on the proximity of the body's centre of mass (COM) position and velocity to the ExFSR limits. We quantified perturbed walking of fifteen non-disabled individuals and three individuals with a disability, and calculated our proposed ExFSR-based measures. 17.2% (32.5%) and 26.3% (34.0%) of the measured trajectories of the COM position and velocity during low (high) perturbations went outside the ExFSR limits, for non-disabled and disabled individuals, respectively. Besides, our proposed measures significantly correlated with measures previously suggested in the literature to assess gait stability, indicating a similar trend in gait stability revealed by them. The ExFSR-based measures facilitate our understanding on the biomechanical mechanisms of loss-of-balance and can contribute to the development of strategies for balance assessment.

A method to estimate inertial properties and force plate inertial components for instrumented platforms.

Kinetic data acquired from force plates embedded in moving platforms naturally contain artifacts due to platform acceleration, called force plate inertial components. While they can be estimated and removed from the measured signals, the system's inertial properties need to be known. Our objective was to: (1) develop a method for estimating the inertial properties and force plate inertial components for any instrumented platform; (2) estimate the inertial properties specifically for the Computer-Assisted Rehabilitation Environment (CAREN); and (3) validate the estimates with new experimental data. Unloaded ramp-and-hold perturbations (for estimation) and unloaded random perturbations (for validation) were executed to obtain the force, moment, and motion of the CAREN platform. Inertial properties were estimated by minimizing the error between the measured and computed inertial forces and moments. Obtained estimates were validated by calculating the coefficient of determination (R2) between the measured and computed forces or moments when keeping the inertial properties fixed. The estimates of the CAREN's inertial properties exhibited low variability across trials, and R2 for the validation trials was 0.90 ± 0.08 (mean ± standard deviation). The developed method can be used for removing inertial components from force plate signals, yielding reliable estimates of ground reactions in dynamic biomechanical research and clinical assessments.