Understanding the effects of a sudden directional shift in somatosensory feedback and increasing task complexity on postural adaptation in individuals with and without chronic ankle instability.

Individuals with chronic ankle instability (CAI) present somatosensory dysfunction following an initial ankle sprain. However, little is known about how individuals with CAI adapt to a sudden sensory perturbation of instability with increasing task and environmental constraints to maintain postural stability. Forty-four individuals with and without unilateral CAI performed the Adaptation Test to a sudden somatosensory inversion and plantarflexion perturbations (environment) in double-, injured-, and uninjured- limbs. Mean sway energy scores were analyzed using 2 (group) × 2 (somatosensory perturbations) × 3 (task) repeated measures analysis of variance. There were significant interactions between the group, environment, and task (P =.025). The CAI group adapted faster than healthy controls to a sudden somatosensory inversion perturbation in the uninjured- (P =.002) and injured- (P <.001) limbs, as well as a sudden somatosensory plantarflexion perturbation in the double- (P =.033) and uninjured- (P =.035) limbs. The CAI and healthy groups presented slower postural adaptation to a sudden inversion perturbation than a sudden somatosensory plantarflexion perturbation in double-limb (P <.001). Whereas both groups demonstrated faster postural adaptation to a sudden somatosensory inversion perturbation compared to somatosensory plantarflexion perturbation while maintaining posture in the injured- (P <.001) and uninjured- (P <.001) limbs. The CAI and healthy groups adapted faster to a sudden somatosensory inversion perturbation in the injured- (P <.001) and uninjured- (P <.001) limbs than in double-limb, respectively. Postural adaptation in individuals with and without CAI depended on environmental (somatosensory perturbations) and task constraints. The CAI group displayed comparable and faster postural adaptation to a sudden somatosensory inversion and plantarflexion in double-, injured-, and uninjured- limbs, which may reflect a centrally mediated alteration in neuromuscular control in CAI. • The group differences in postural adaptation were affected by task & environmental constraints. • CAI showed faster postural adaptation in the injured- and uninjured- limbs when perturbed to inversion. • CAI showed faster postural adaptation in the uninjured-limb when perturbed to plantarflexion. • Postural adaptation altered in both groups as the direction of perturbations changed. [ABSTRACT FROM AUTHOR]