Objective: The purpose of this investigation was to document the isokinetic performance deficiencies of the invertor and evertor muscles of chronically sprained ankles.

Method: Eversion/Inversion testing was performed by a Cybex 6000 isokinetic dynamometer at the speeds of 60^o/sec and 120^o/sec on 17 subjects who had unilateral chronic ankle sprain. Values were compared between the involved and uninvolved sides.

Results: The inversion peak torque deficits between the involved and uninvolved extremities were significantly greater than eversion deficits at 60^o/sec and 120^o/sec. Evertor/Invertor peak torque ratios of involved sides at 60^o/sec were significantly greater than uninvolved sides.

Conclusion: We conclude that chronic ankle sprains associate an ankle invertor weakness rather than an evertor weakness. Ankle invertor weakness might be resulted from a disuse atrophy and painful ankle inversion. Further prospective study is needed to determine the relationship between the invertor weakness and the chronic ankle sprain.