Abstract
Introduction
Chronic ankle instability (CAI) is associated with sensorimotor impairment, altered postural control, and fear-related movement burden. Time-to-boundary (TTB) quantifies postural safety margins by estimating the time available before the center of pressure reaches the boundary of the base of support. However, it remains unclear whether TTB differentiates individuals with CAI from controls during sensory-challenging balance tasks. Therefore, this pilot study compared TTB outcomes between adults with and without CAI across six Clinical Test of Sensory Interaction and Balance (CTSIB) conditions and explored associations between TTB, physical activity, and fear-related outcomes within the CAI group.
Methods
Twenty middle aged adults (40-59 years old) were included: CAI (n = 10) and control (n = 10). Participants completed six double-leg CTSIB conditions while standing on a force plate: firm surface with eyes open (T1), eyes closed (T2), and visual conflict (T3), and foam surface with eyes open (T4), eyes closed (T5), and visual conflict (T6). Center-of-pressure data were used to calculate absolute minimum TTB in the mediolateral (ML) and anteroposterior (AP) directions for each condition. Physical activity variables included moderate-to-vigorous physical activity, steps, and energy expenditure which were collected using a waist-worn ActiGraph wGT3X-BT accelerometer (ActiGraph LLC, Pensacola, FL, USA). Fear-related outcomes included the Tampa Scale of Kinesiophobia and Fear-Avoidance Beliefs Questionnaire. Separate 2 × 6 repeated-measures ANOVAs examined the effects of group and condition on ML and AP TTB. Exploratory Spearman correlations examined associations among TTB, physical activity, and fear-related outcomes within the CAI group.
Results
TTB varied significantly across CTSIB conditions in both directions. ML TTB demonstrated a significant main effect of condition (Pillai’s Trace = 0.872, F(5,14) = 18.998, p 0.001, ηp² = 0.872), but no significant group effect, (F(1,18) = 0.594, p = 0.451, ηp² = 0.032) or condition × group interaction (Pillai’s Trace = 0.165, F(5,14) = 0.555, p = 0.733, ηp² = 0.165). AP TTB also demonstrated a significant main effect of condition Pillai’s Trace = 0.869, F(5,14) = 18.572, p 0.001, ηp² = 0.869), but no significant group effect (F(1,18) = 0.053, p = 0.820, ηp² = 0.003) or condition × group interaction (Pillai’s Trace = 0.373, F(5,14) = 1.663, p = 0.208, ηp² = 0.373). TTB generally decreased as sensory demands increased, particularly during foam and visual-conflict conditions. In exploratory CAI-only analyses, TTB was associated with physical activity and fear-related outcomes. Greater moderate-to-vigorous physical activity and energy expenditure were associated with higher AP TTB during firm eyes-open standing (ρ = 0.685–0.794, p = 0.006–0.029). Higher kinesiophobia and fear-avoidance were associated with lower TTB across sensory-challenging conditions (ρ = −0.644 to −0.911, p 0.001–0.044).
Discussion: TTB varied significantly across sensory conditions, indicating that sensory difficulty influenced postural safety margins. However, adults with and without CAI did not differ in ML or AP TTB during double-leg CTSIB testing, suggesting that double-leg TTB may be more sensitive to sensory task demands than CAI group status in this pilot sample. Lower TTB appears to contribute to greater kinesiophobia and fear-avoidance as well as lower moderate-to-vigorous physical activity in people with CAI.