The aim of this study was to evaluate the effect of balance surface type on muscle activity of ankle stabilizing muscles in subjects with chronic ankle instability. 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 examine 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. There weren’t any differences 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 exhibited the lowest tibialis anterior/peroneus longus muscle ratio, followed by balancing along a frontal axis and on the Airex pad.
Clinicians can use these findings to improve the focus of balance training programmes by gradually increasing the level of difficulty based on muscle activation levels taking co-contraction ratios into account.