# Distinct patterns in neuromuscular adaptation to repeated perturbations in chronic ankle instability

## TL;DR

People with chronic ankle instability show different muscle adaptation patterns during repeated perturbations compared to healthy individuals, suggesting a need for targeted rehabilitation strategies.

## Contribution

The study identifies distinct neuromuscular adaptation patterns in chronic ankle instability during repeated perturbations.

## Key findings

- CAI individuals showed different adaptive changes in muscle co-contraction compared to healthy controls.
- Healthy controls reduced TA-PL co-contraction with practice, while CAI individuals did not.
- Repeated perturbations improved postural control and hip strategy in CAI individuals.

## Abstract

Neuromuscular impairments following ankle sprains are central to chronic ankle instability (CAI), potentially leading to compensatory muscle co-contraction to regulate ankle stiffness, particularly in response to external perturbations. The acute effect of practice on muscle activation and postural responses reveal initial deficits in motor control and indicate the capacity of individuals with CAI to overcome these deficits within their specific constraints. This study aimed to examine adaptive changes in lower limb muscle co-contraction between CAI and healthy control (HC) participants during repeated perturbations and assess whether practice influences postural control and strategy.

Twenty-three CAI and 23 HC participants performed a single-leg balance task involving repetitive mediolateral perturbations. Surface electromyography, ground reaction force and whole-body kinematics were recorded, and margin of stability (MoS) and the coupling between MoS and ankle-/ hip-joint torques were calculated.

Individuals with CAI demonstrated different adaptive changes in muscle co-contraction for Tibialis Anterior (TA) - Peroneus Longus (PL) and TA - Soleus compared to HC. In healthy controls, TA-PL co-contraction decreased significantly with practice, while no changes were observed in the CAI group. Repeated perturbations improved MoS and MoS-Hip torque coordination in CAI, suggesting improved postural control and hip strategy.

Rehabilitation for CAI should target both the whole-body coordination and ankle adaptation exercise since ankle joint appears refractory to change in CAI individuals. Future research should explore whether co-contraction patterns influence risk of ankle sprain in CAI populations, linking lab-based performance to real-world injury risks.

The online version contains supplementary material available at 10.1186/s12984-025-01838-y.