Bilateral compensatory postural adjustments to a unilateral perturbation in subjects with chronic ankle instability.

BACKGROUND: To evaluate the magnitude of bilateral compensatory postural adjustments in response to a unilateral sudden inversion perturbation in subjects with chronic ankle instability.

METHODS: 24 athletes with chronic ankle instability (14 with functional ankle instability, 10 with mechanical ankle instability) and twenty controls participated in this study. The bilateral electromyography of ankle muscles was collected during a unilateral sudden ankle inversion to assess the magnitude of subcortical and voluntary compensatory postural adjustments in both the perturbed and the contralateral limb (support limb).

FINDINGS: In the support position, compared to the control group, the group with functional ankle instability presented decreased compensatory postural adjustments of the tibialis anterior in both the injured and the uninjured limbs in the support position and of the soleus in the uninjured limb. In the side of the perturbation, participants with functional ankle instability presented decreased soleus compensatory postural adjustments in the uninjured limb when compared to the control group. Increased values of soleus and peroneal brevis compensatory postural adjustments were observed in the group with mechanical instability when compared to the control group and to the group with functional ankle instability.

INTERPRETATION: Subjects with functional ankle instability present bilateral impairment of compensatory postural adjustments of the tibialis anterior in a support position and of the soleus of the uninjured limb regardless of the position. Subjects with mechanical instability present bilateral increase of these adjustments in the peroneal brevis regardless of the position and in the soleus muscle in the side of the perturbation.