Alteration of ankle kinematics and muscle activity during heel contact when walking with external loading.

PURPOSE: The risk of recurrent ankle sprains could be reduced if the ankle joint is positioned in a more closed pack position (eversion and dorsiflexion) with enhanced co-activation of Tibialis Anterior (TA) and Peroneus Longus (PL) around heel contact in walking. We examined whether such alteration can be induced by augmenting ankle position error in the inversion and plantarflexion directions. METHODS: Fifteen young, healthy subjects participated in this study. They walked on a treadmill while a light weight was affixed to the dorsal-lateral side of the test foot to create afferent error signals in the inversion and plantarflexion directions. We recorded and analyzed subjects' ankle kinematics and electromyographic (EMG) activity of TA and PL before (baseline), during (adaptation), and after (post adaptation) walking with the weight. Our analyses focused on 30 ms before and after heel contact where ankle sprains are most likely to occur. RESULTS: Subjects increased ankle eversion before and after heel contact during the adaptation period. This increase carried over to the post adaptation period following removal of the weight. The weight also induced an increase in the TA activity before heel contact during late adaptation, although this increase did not carry over to the post adaptation period. No significant changes were observed in ankle dorsiflexion, PL activity, and muscle co-activation. CONCLUSION: Our error-driven approach is feasible to reduce ankle inversion around heel contact in walking, and may have clinical implication on intervention of recurrent ankle sprains.