Virtual pivot point: Always experimentally observed in human walking?

Abstract

A main challenge in human walking is maintaining stability. One strategy to balance the whole body dynamically is to direct the ground reaction forces toward a point above the center of mass, called virtual pivot point (VPP). This strategy could be observed in various experimental studies for human and animal gait. A VPP was also observed when VPP input variables like center of mass or ground reaction forces were perturbed. In this study, the kinetic and kinematic consequences of a center of pressure manipulation and the influence on the VPP are investigated. Thus, eleven participants walked with manipulated center of pressure (i.e. barefoot, backwards, with a rigid sole, with stilts, and in handstand compared to shoe walking). In all conditions a VPP could be observed, only one participant showed no VPP in handstand walking. The vertical VPP position only differs between shoe walking and rigid sole walking, there are no significant differences between the conditions in the horizontal VPP position and the spread around the VPP. However, it is conceivable that for more severe gait changes, walking without VPP could be observed. To further analyze this issue, the authors provide a VPP calculation tool for testing data regarding the existence of the VPP.

The virtual pivot point concept improves predictions of ground reaction forces

“…During walking, the GRFs converge at a point above the center of mass, indicating a pivotal location, the VPP, where the forces intersect ( Gruben and Boehm, 2012 ). The observed vertical position of the VPP varies between studies, due to the different walking speeds and curb height or manipulating the center of pressure ( Müller et al, 2017 ; Vielemeyer et al, 2019 ; 2023a ). In contrast, during running, the GRFs intersect below the center of mass, indicating a distinct biomechanical characteristic ( Drama et al, 2020 ).…”