Comparative Analysis of Dynamic Balance Descriptors in Humanoids and Humans During Perturbed Bipedal Locomotion and Fall

This study identifies a robust parameter for quantifying instability in general biped systems by comparing three mechanical stability descriptors: the distance between the center of mass to the minimal moment axis (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d_{\text{Com-max }}$</tex>), the margin of stability (MoS), and whole-body angular momentum (WBAM) in both humans and humanoid biped robots. We analyzed these metrics during normal and perturbed walking, including robot falls, a dynamic whose observation is limited in human trials due to safety concerns. Our comparative analyses demonstrate that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d_{\text{COM-MMA }}$</tex> is more predictive of different levels of instability and shows a clearer distinction between fall and non-fall states, compared to MoS and WBAM. These findings were consistent for both humans and biped robots, regardless of gait variability or the type and intensity of the perturbation methods. These qualities highlight its potential use in unified stability analysis in both fields, offering insights that can inform the design of exoskeletons, fall monitoring systems, and other gait-assistive devices for aging populations.