Effects of Functional Fatigue Protocol and Visual Information on Postural Control in Patients with Chronic Ankle Instability

Chronic ankle instability (CAI) patients often exhibit postural control deficits and rely on visual information to maintain static balance to compensate for decreased proprioception. Fatigue impairs neuromuscular control, in addition to postural control, in CAI patients. However, whether functional fatiguing exercises alter postural control and sensory organization strategies during single-leg balance tests in CAI patients remains unclear. This study involved a controlled trial on 28 CAI patients in a laboratory setting. Each participant performed a single-leg balance test with eyes open (EO) and eyes closed (EC) before and after a functional fatigue protocol. Two-way repeated-measures ANOVA evaluated fatigue (pre- vs. post-fatigue) × vision (EO vs. EC) interactions for outcome variables. Additionally, paired-sample t-tests examined differences between two conditions (pre- vs. post-fatigue) for time-to-boundary (TTB) minima (%modulation). We found significant interactions between fatigue and vision conditions in ML and AP TTBmeans and AP TTBsds. %Modulations were significantly decreased after fatigue in AP TTBmean, ML TTBsd, and AP TTBsd. In conclusion, static postural control ability decreased after the functional fatigue protocol with EO, but was unchanged with EC. This suggests that decreased balance ability is more pronounced with EO under fatigue due to less visual dependence. This may increase ankle sprain incidence under fatigue.