Biomechanics of ankle instability. Part 1: Reaction time to simulated ankle sprain

To test the hypothesis that ankles with functional instability will demonstrate slower muscular reaction times than their contralateral stable ankle (SA) and stable healthy controls to a simulated nonpathological ankle sprain mechanism.

Nineteen male volunteers with a history of unilateral ankle sprain and functional ankle instability (FAI) and 19 healthy male controls performed reaction time tests on a purpose-built platform that simulated a nonpathological combined inversion/plantarflexion ankle sprain mechanism. Participants provided informed written consent. Reaction time and muscle activity magnitude data were reported for the FAI group's unstable (UA) and stable ankles (SA) and the control group's dominant (DA) and nondominant ankles (NDA) to unilateral simulated ankle sprain (USAS).

The reaction times of the peroneus longus (PL), peroneus brevis (PB), and tibialis anterior (TA) in the UA were significantly slower (P < 0.025) than the SA and control group's DA in the limb experiencing USAS. The reaction times of the support limb PL, TA, and extensor digitorum longus (EDL) muscles of the UA were slower than the DA (P < 0.025). The magnitude of EMG response was not different between the SA and UA (P > 0.025).

Results demonstrate a deficit (slower reaction time) in ankles with FAI when acting in support and when exposed to a simulated sprain compared to stable healthy controls. As a result of slower reaction times, acting to support the UA may put the contralateral SA at an increased risk of ankle sprain. This suggests that rehabilitation of a lateral ankle sprain should include strengthening the evertors (peroneals and EDL) at the subtalar joint and the dorsiflexors (TA and EDL) at the talocrural joint.