A comparison of anticipatory processes between gait and step initiation: The role of the final state

Abstract

Background

Whole-body movement initiation with change of base of support is a common paradigm used to assess balance-movement coordination. During clinical evaluation, two transitions are commonly used: gait or step initiation. During their respective anticipatory periods, two mechanisms regulate the whole-body centre of mass acceleration: a shift in the centre of pressure (CoP); and modulation of internal whole-body angular momentum ($H_M$). These transitions have different final states, and we do not know whether the two mechanisms are used similarly during the anticipatory period.

Research question

Is the final state already taken into account during the anticipatory period of a whole-body movement initiation?

Methods

We compared the time evolution of the CoP and $H_M$ in the sagittal plane during the anticipatory period of both gait and step initiation in 13 young, healthy participants.

Results

During gait initiation, we observed a larger backward CoP shift (31–56 % and 75–100 % of the anticipatory period), a larger forward-directed $H_M$ (45–68 %), and a lower backward-directed $H_M$ (84–100 %) compared to step initiation.

Significance

Our results show that mechanical instability is larger during gait initiation, while $H_M$ modulation is larger during step initiation. These findings suggest that the final state of a transition is taken into account during the anticipatory period. Based on our results, we suggest future research should use gait and step initiation to evaluate the generation of mechanical instability, and the use of free segments, respectively, in populations with balance deficits.