The Effect of Sudden Inversion Stress on EMG Activity of the ~ uscles in the

nkle sprains perhaps are frequently the most common injury experienced by athletes. It has been documented that up to 85% of injuries to the ankle involve the lateral structures resulting from the combined motions of plantar flexion and inversion (2). Damage to the lateral structures often results in disability, which can be found in up to 40% of individuals who have experienced injury to the lateral ligaments of the ankle (1). The term "functional instability" was first suggested by Freeman et al (6) to describe ankles which suffered recurrent sprains or had the tendency to "give way." Although the etiology of this chronic disability is still unknown, several causes have been suggested, including mechanical instability, muscle weakness, and proprioceptive deficits resulting in motor incoordination, thereby predisposing the ankle to functional instability (4.6.7). Previous studies have suggested that muscle weakness, particularly in the peroneal muscles, may play a significant role in the etiology of functional instability, although this notion is still under debate (1,11,13). Some have also proposed that the reflex time of the peroneal muscles as opposed to the absolute strength Chronically Unstable Ankle