Influence of balance surface on ankle stabilizing muscle activity in subjects with chronic ankle instability.

OBJECTIVE To evaluate the effect of balance surface type on muscle activity of ankle stabilizing muscles in subjects with chronic ankle instability. DESIGN Case-controlled, repeated-measures study design. SUBJECTS Twenty-eight subjects with chronic ankle instability and 28 healthy controls. METHODS Subjects performed a barefooted single-legged stance on uniaxial and multidirectional unstable surfaces. Muscle activity of the mm. peroneus longus/brevis, tibialis anterior, gastrocnemius medialis were registered using surface electromyography. Mixed model analysis was used to explore differences in muscle activity between subjects with chronic ankle instability and controls, and the effect of surface type on muscle activity levels within subjects with chronic ankle instability. RESULTS No differences were found between subjects with chronic ankle instability and healthy controls. Within subjects with chronic ankle instability, balancing along a frontal axis and on the Both Sides Up evoked overall highest muscle activity level, and the firm surface the least. Balancing on the firm surface showed the lowest tibialis anterior/peroneus longus muscle ratio, followed by balancing along a frontal axis and on the Airex pad. CONCLUSION Clinicians can use these findings to improve the focus of balance training programmes by gradually progressing in difficulty level based on muscle activation levels taking co-contraction ratios into account.