Comparison of Strength and EMG Activity of Shoulder Flexor Muscles and Scapular Winging in Subjects with and without a Winged Scapula during Shoulder Flexion

Comparison of Strength and EMG Activity of Shoulder Flexor Muscles and Scapular Winging in Subjects with and without a Winged Scapula during Shoulder Flexion

Background Subjects with a winged scapula (WS) can cause musculoskeletal disorders of the shoulder due to uncontrolled movement of the scapula during shoulder flexion. A WS results in abnormal positioning of the scapula, leading to shoulder dysfunction. Objectives This study is to compare shoulder flexion strength, electromyography (EMG) activity of the periscapular muscles, and scapular winging during shoulder flexion in subjects with and without a WS. Methods Twelve with and thirteen without a WS participated in this study. To compare shoulder flexion strength, muscle activity, and scapular winging between the two groups, maximal flexion was measured using a tensiometer during shoulder flexion. Concurrently, surface EMG was used to measure the activities of the upper trapezius (UT), anterior deltoid (AD), serratus anterior (SA), and lower trapezius (LT) muscles, and a scapulometer was used to measure scapular winging during shoulder flexion. The independent t-test was used to compare shoulder flexion strength, muscle activity, and scapular winging between the two groups. Results There was no significant difference in shoulder flexion strength between the two groups (p = 0.172). The activities of the SA and UT muscles decreased significantly in subjects with a WS compared to subjects without a WS (p = 0.001 vs p = 0.023). In addition, scapular winging was significantly greater in subjects with a WS compared to those without a WS (p = 0.001). Conclusions These findings muscle activities of the SA and UT in subjects with WS is associated with upward rotation of the scapula and scapular winging rather than shoulder flexion strength. This may be supporting evidence for exercises reflecting the degree of activity of the muscles around the shoulders rather than focusing on the shoulder flexor during physical therapy related to shoulder flexion in a clinical setting.