# The effects of anticipation of standing surface translations on distal leg muscle excitations

## TL;DR

This study explores how anticipating surface movements during standing affects muscle activity in the legs, particularly in response to forward and backward perturbations.

## Contribution

The study reveals direction-dependent and anticipation-driven neuromuscular responses to surface translations during standing.

## Key findings

- Anticipated balance challenges increased proactive muscle activity in all tested muscles.
- Unanticipated forward perturbations caused greater reactive activity in the tibialis anterior compared to anticipated ones.
- Proactive adjustments for forward surface translations effectively reduced backward center of mass displacement.

## Abstract

This study aimed to investigate the interactions between anticipation and direction of surface translations applied during standing on distal leg muscle excitations measured via surface electromyography (EMG) in the context of resultant changes in center of mass (CoM) displacements. Twenty young adults experienced four combinations of surface translations (i.e., anticipated anterior, unanticipated anterior, anticipated posterior, unanticipated posterior) via a dual-belt instrumented treadmill. For each condition, a 200 ms, 6 m/s2 anterior or posterior perturbation was delivered either unexpectedly or after a three-second verbal countdown. Each condition was repeated three times in a randomized order. We recorded surface EMG from the MG, SOL, and TA, and motion capture collected pelvis displacements as a surrogate for CoM. Data were analyzed across three time periods: pre-perturbation, early post-perturbation, and late post-perturbation. Direction-dependent EMG responses were as hypothesized, with TA iEMG increasing by 81% following anterior perturbations and MG and SOL iEMG increasing by 60% and 32% respectively following posterior perturbations. As hypothesized, anticipated balance challenges elicited greater proactive iEMG for all muscles. However, only unanticipated anterior perturbations elicited greater reactive TA iEMG than anticipated anterior perturbations. These proactive neuromechanical adjustments, particularly for anterior surface translations that would precipitate a backward fall, appeared protective and effective based on resultant patterns of CoM displacements. These data serve as a reference for understanding how aging and disease impact proactive and reactive postural control, especially for populations who may have difficulty with both the planning and execution of corrective neuromuscular adjustments.

The online version contains supplementary material available at 10.1007/s00221-025-07075-y.