The Relationship between Activity Level of Some Lower Extremity Muscle and Anterior Shear Force during Single-Leg Jump Landing

Abstract Introduction: Identifying factors which cause the high incidence of ACL is of great importance .The anterior shear forces are the primary mechanism of load sustained on the ACL. During exercise, the activity of muscles and position of lower limbs may increase or decrease the anterior shear force. The purpose of this study is to investigate the relationship between the activity level of some lower extremity muscles and anterior shear force during single-leg jump landing. Materials and Methods: Twenty male-students of physical education participated in this study. EMG activity of the muscles of the gluteus medius, tibialis anterior and hamstring were evaluated via Electromyography system and ground reaction force was evaluated via force plate system in jump-landing task. There was used Pearson correlation test. Results: The results indicated no significant correlation between tibialis anterior and gluteus medius muscles activity with shear force, while there was found correlation between lateral hamstring muscle activity and anterior shear force (P< 0.05). Conclusion: The findings of this study showed that hamstring muscle activity during single-leg jump landing acts as a supporting muscle of ACL.This increased muscle activity leads to the reduction of the load on the ACL. Keywords: Electromyography, Anterior Shear Force, Anterior Cruciate ligament, Jump-Landing task, Lower Extremity Muscle