엎드려 팔 들기 운동시 팔꿈치 굽힘 각도 변화에 따른 위등세모근, 아래등세모근, 가시아래근의 근활성도 및 위⋅아래등세모근의 비율 비교

Comparison of Upper and Lower Trapezius and Infraspinatus Muscle Activation and UT/LT Ratio in Response to Changes in Elbow Flexion Angle During the Prone Arm Lift Exercise

Background Optimal shoulder function necessitates both proper scapular alignment and appropriate muscle coordination. Excessive muscle activation of the upper Trapezius (UT) and decreased muscle activation of the lower Trapezius (LT) can lead to changes in scapulohumeral rhythm and kinematic dysfunction. Many studies suggest that arm lift exercises are known to selectively strengthen the LT. However, research on exercise strategies that reduce overall torque/loading by altering the position of distal upper limb segments (elbow flexion) to minimizing overactive UT compensation is limited. Objectives To investigate the effect of changes in elbow flexion angle during prone arm lift exercise on the muscle activity of the UT, LT, and infraspinatus (IS) muscles, and the muscle activity ratio of the UT/LT muscles. Methods A total of 18 healthy adults were recruited as participants. Muscle activation was measured using Delsys surface electromyography system. Electromyographic data were collected while participants performed the arm lift exercise at three different elbow flexion angles: 90°, 40°, 0° Results Significant differences were confirmed across the three elbow flexion angles for the UT (p < 0.001), LT (p < 0.001), IS (p = 0.03), and Ratio (p = 0.001). Post-hoc analysis revealed that for the UT, significant differences were found between 90° and 40° (p = 0.003), 90° and 0° (p < 0.001), and 40° and 0° (p < 0.001). For the LT, differences were observed between 90° and 40° (p < 0.001), 90° and 0° (p < 0.001), and 40° and 0° (p = 0.001). For the IS, a difference was only noted between 40° and 0° (p = 0.014). And for the Ratio, significant differences were found between 90° and 0° (p = 0.002) and 40° and 0° (p = 0.001). Conclusions The increased elbow flexion effectively reduced the lever arm length, consequently lowering overall muscle activation. Crucially, this strategy was confirmed to significantly decrease the UT/LT ratio. These findings propose a method to inhibit UT activity while selectively strengthening the LT during the prone arm lift exercise.