Background : Acute lateral ankle sprains are the most common injuries in sports and routine activities of life. The purpose of this study was an overview of EMG activation of postural stabilizer muscles in dynamic balance test to provide clinicians with biomechanical perspectives of the local and global effects of ankle instability.

  Methods : The sinker– card protocol was used as a dynamic balance test with simulating fall upon 4 posture stabilizer muscles medialis gastrocnemius (MG), tibialis anterior (TA), vastus medialis (VM) and erector spine in L3 during sudden acceleration in base of support, in two sides of the body (involved, uninvolved or left, right) in sudden acceleration in forward and backward directions. The study was conducted on 19 adult men in two groups (9 LAS subjects with the mean of age 23/9 ± 2/03 yrs and 10 normal subjects with the mean of age 26/4 ± 3/20 yrs). The data of EMG were assessed using one- way repeated measures 2×2×4 ANOVA and multivariate analysis of variance (p< 0.05).

  Results : Higher TA activity in LAS group rather than normal group in forward direction was significantly illustrated. Higher MGR activity in normal group than LAS group in backward direction was significantly illustrated. The EMG activity of two sides of body in two directions were significantly symmetric in LAS group.

  Conclusion : Acute ankle instability with alternation in neuromusculoskeletal system can affect on dynamic balance control in patient with lateral ankle sprains.