Ankle muscle activation during the limits of stability test in subjects with chronic ankle instability.

Objective: To study postural control and muscle activity during the limit of stability test (LOS) in subjects with chronic ankle instability.

Design: Observational study.

Setting: University laboratory.

Participants: 10 healthy subjects were included in the control group and 10 subjects in the CAI group (age between 18 and 30 years, with history of the multiple ankle "giving way" episodes in the last six months and score ≤24 in the Cumberland Ankle Instability Tool).

Main Outcome Measures: A computerized dynamic posturography equipment was used for assessing the LOS. The electromyography activity of tibialis anterior (TA), soleus (SOL), medial gastrocnemius (MG) and peroneus longus (PL) was registered.

Results: Subjects with CAI had a greater activation in TA to forward (p < .01), forward affected (p = .001), backward affected (p = .007) and backward directions (p < .01); in PL to forward affected (p < .01) and affected directions (p = .001); in MG to forward (p = .023) and affected directions (p < .01) and in SOL to the affected direction (p = .009). We observed restricted excursions and less directional control in subjects with CAI.

Conclusions: Subjects with CAI exhibited poorer ability to move their center of gravity within stability limits. In addition, they have an altered ankle muscle activity during LOS test toward the affected ankle joint.