[Purpose] This study examined the effects of 4-week of balance exercise with medio-lateral unstable sole on ankle muscle activation and functional ability. [Subjects and Methods] Thirty university students without current or past ankle injuries were assigned to either an experimental group or control group. The experimental group participated in a balance exercise program 3 times a week over 4 weeks, which consisted of one-leg stands and semi-squat exercises with medio-lateral unstable sole. The control group continued with their regular life activities without participation in the program. Electromyographic activities of peroneus longus and brevis muscles were recorded during stair descending immediately before and after the exercise program. Functional balance was tested with the Star Excursion Balance test immediately before and after the exercise program. Paired t-tests were used to assess statistical significance. [Results] Activation of peroneus longus and brevis and Star Excursion Balance Test scores in both groups did not show a significant difference between pre- and post-exercise. [Conclusion] A future study is suggested with increased level of medio-lateral perturbation during outcome measurements and exercises with addition of supervision in the exercise training and home program.

[Purpose] The purpose of this study is to research the most effective knee flexion angle and ground condition in the squat position. [Subjects and Methods] The subjects of this study were 15 female college students who were able to perform squat movements and who had never previously experienced surgery, orthopedic disease, or musculoskeletal impairment. This study was conducted to examine changes of muscle activation of low-extremity muscles at different knee flexion angles of 70°, 90°, and 100°. Balance Pad (Aero Step, TOGU, Germany) was used as unstable ground. Surface electromyogram (4D-MT & EMD-11, Relive, Korea) was used for measuring muscle activation. Measured muscles were vastus medialis, biceps femoris, tibialis anterior, and gastrocnemius. Muscle activation was determined by the root mean square (RMS). [Results] There was a difference in muscle activation of the vastus medialis and tibialis anterior according to the change of the knee flexion angle with the stable ground. However, there was no difference in muscle activation of the lower extremity muscles according to the change of the knee flexion angle with the unstable ground. [Conclusion] These results suggest that changes in the angle of the knee flexion with the stable ground affect the muscle activation of the vastus medialis and tibialis anterior. It was found that as the joint angle increases, muscle activation also increases. However, ground condition does not affect muscle activation.