Cognitive Loading Produces Similar Change in Postural Stability in Patients With Chronic Ankle Instability and Controls

Abstract

Purpose: While postural stability is compromised in individuals with chronic ankle instability (CAI), few studies have attempted to examine how performing simultaneous cognitive and balancing tasks may alter the complexity of the center of pressure. The purpose of this study was to compare postural stability in patients with CAI to controls during a dual-task condition via sample entropy.

Methods: Thirty participants (15 CAI, 15 healthy control) performed 3-trials of single-leg stance for 60-seconds each under two different conditions: single-task and dual-task (serial subtraction). Sample entropy (SampEn), a measure of pattern regularity, was calculated from the center of pressure excursion in the anterio-posterior (AP) and medio-lateral (ML) directions. 2x2 mixed-model ANOVAs determined any differences by task or group (p≤0.05).

Results: SampEn-AP decreased in the dual-task condition compared to single-task, single-leg balance across groups (F_1,28=8.23, p=0.008, d=0.53). A significant interaction for group by task was found for SampEn-ML (F_1,28=4.18, p=0.05), but post hoc testing failed to reveal significant differences. Serial subtraction was completed with significantly fewer errors during dual-task compared to single-task (F_1,27=12.75, p=0.001, d=0.66).

Conclusions: Patients with CAI do not display differences in regularity of postural stability, even when attention is divided. However, the addition of serial subtraction increased the regularity of AP center-of-pressure motion. Increased regularity may suggest a change in motor control strategy, reducing natural fluctuations and flexibility within movement patterns during more challenging tasks. Clinicians could utilize dual-task situations during rehabilitation of patients with CAI, in order to adequately restore stability and function when attention is divided.

Figure 1:

Box plots demonstrating the main effect for task in the anterior-posterior direction. The dual-task condition resulted in a lower SampEn-AP compared to a single-task, regardless of group. Both groups (CAI and control) are presented to better visualize the data.

Figure 2:

Significant interaction for task and group for SampEn-ML. Post-hoc testing did not reveal significant changes between tasks in either CAI or control groups, despite the visual interaction. The lines represent the CAI (dashed) and control (solid) groups on each task (s.d. error bars).