ANKLE MUSCULATURE LATENCY MEASUREMENT TO VARING ANGLES OF SUDDEN EXTERNAL OBLIQUE PERTURBATION IN NORMAL FUNCTIONALLY UNSTABLE ANKLES

Background: Several studies have examined the reflex response of ankle musculature to sudden inversion in noninjured and injured subjects. To date, there have been no studies to determine the effect of versatile degrees & conditions of perturbation on the ankle musculature latency. The purpose of this study was to measure and determine whether there was a difference in ankle musculature latency measurements at 10°, 20°, and 30° in the oblique plane on a dual tilting platform (APS) between normal and functionally unstable ankles under different conditions of perturbation. Methods: The musculature latency of 15 healthy subjects (8 females, 7 males; age range, 18 to 30 years) and 15 patients with functional ankle instability (FAI) (8 females, 7 males; age range, 18 to 30 years) were examined with surface EMG after sudden inversion of the ankle by APS. Results: In all angles of the oblique plane, the latency of Peroneus longus, Tibialis anterior, Peroneus brevis, and Soleus were significantly longer in subjects with unstable ankles under expected and unexpected conditions. Unexpected conditions led to increase the latency of ankle musculature, both for normal and functionally unstable ankles. Conclusion: The significantly longer onset and peak latency of ankle musculature during sudden inversion in the standing position in subjects with unstable ankles is explained by proprioceptive deficit in sensorimotor control of functionally unstable ankles. Unexpected external perturbations of body equilibrium elicit compensatory postural reflexes which cause longer latency of ankle musculature during varying angles of perturbation.