Comparative Methodological Approaches for Analyzing Margin of Stability During Normal Walking

A comprehensive evaluation of pathological gait patterns is essential for understanding the underlying pathology and its progression to deliver personalized treatments. One quantitative indicator for assessing fall risks during walking is margin of stability (MoS), a measure of instantaneous mechanical stability derived from the dynamic relationship between the extrapolated center of mass (CoM) and the center of pressure. However, extrapolating CoM during movement is not straightforward, and there is an undesired variability induced by the selected measurement protocol, which often depends on the available technology. Up until now, the extent of this variability has not been investigated systematically. This study compares four different CoM estimation methods. Based on the Conventional Gait Model, the first two methods estimate CoM using virtual sacrum (1) and pelvis centroid (2). The third method estimates CoM from ground reaction force (3), and the last method uses the accelerometer and gyroscope data from a smartphone mounted on the lower back. 21 healthy subjects (10 female, 11 male, age: 31.7 ± 9.0 years; BMI: 24.7 ± 3.5 kg m-²) walked on an instrumented treadmill at a fixed speed at 1.3 m s -1 for 3 minutes. Descriptive statistical analysis was performed, including temporal and normalized gait cycle analysis, focusing on the minimum and maximum MoS, and its ranges during walking. SPMld with paired t-tests was employed for the analysis. Our results suggest that CoM estimation varies significantly depending on the selected measurement protocol and technology which should be considered while reporting and interpreting MoS results.