Combined gait asymmetry metric

Abstract

People with physical impairments often have asymmetric gait. To evaluate if their overall symmetry is improving during intervention, there needs to be a simple metric that can help classify gait patterns that includes multiple measures of gait asymmetry. The Combined Gait Asymmetry Metric presented here is based on the Mahalanobis distance of multiple step parameters. We tested able-bodied subjects with perturbations that involve a change in leg length, the addition of ankle weights, and a combination of both perturbations. The Mahalanobis distances are calculated from perfect symmetry to all points in the data to analyze the effects of the different perturbations. The metric demonstrates how an overall view of symmetry can give a better perspective of asymmetry than only looking at a few individual parameters. This metric is straightforward and can be extended to include large numbers of spatiotemporal, kinematic, and kinetic parameters that more completely evaluate a change in gait symmetry.

Comparing Gait with Multiple Physical Asymmetries Using Consolidated Metrics

“…The subsets of the gait parameters can be made to fit the requirements of the clinicians such as reporting on improvements in only spatiotemporal parameters or only in kinematics. For example, in a prior study with CGAM, only 5 gait parameters were used to analyze the data (Ramakrishnan et al, 2016 ). The parameters were step length, step time, vertical forces, push off forces, and braking forces.…”

“…Once the parameters are analyzed, their differences are evaluated for each step using the symmetric index formula (Herzog et al, 1989 ). This asymmetry data is then used to obtain the Combined Gait Asymmetry Metric (CGAM) (Ramakrishnan et al, 2016 ), which is a single number representing an Index/score for the level of asymmetry. The study further compares the CGAM to the machine learning grouping metric with the help of LibSVM library (Chang and Lin, 2011 ).…”

“…The formula for calculating the CGAM distance is shown in Equation (1). The equation presented in this article is modified from the previous version of CGAM (Ramakrishnan et al, 2016 ). This formulation provides more of a weighted means approach to decrease the variability of results for the same gait parameters.…”

“…The precursor to this research study showed that the combined gait asymmetry metric (CGAM) used a symmetry index in conjunction with Mahalanobis distances. Without the restrictions of dimensionality reduction, CGAM served as a versatile gait asymmetry metric (Ramakrishnan et al, 2016 ).…”

Human Gait Analysis Metric for Gait Retraining

“…The modified CGAM [30] works similar to weighted means, but, in this case, the weights are inverse covariances that are multiplied across the dataset in the numerator. To balance the influence of the inverse of covariance, it is divided by the sum of the inverse covariance matrix, equation (2).…”