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영어

Background: The serratus anterior and upper trapezius muscles act synergistically to allow for an appropriate scapulothoracic rhythm. However, a decrease in serratus anterior activation causes the upper trapezius to become overactivated, resulting in dysfunction. This study compared serratus anterior and upper trapezius muscle activity according to sling angle and compared serratus anterior strength between healthy adults and patients with shoulder instability. Methods: Twenty participants (10 healthy adults and 10 patients with shoulder instability) were included in this study. The participants had their arms extended at sling angles of 30°, 60°, and 90° in reach forward with shoulder flexion using goniometer. Serratus anterior strength was measured three times while the participants were supine. The outcome measures were surface electromyography amplitude of the upper trapezius and serratus anterior and serratus anterior strength. Results: The Wilcoxon signed-rank test indicated that the upper trapezius was significantly different between healthy group and shoulder instability group at a sling angle of 60°, and both the upper trapezius and serratus anterior exhibited significant differences at 90°. Moreover, a significant difference was noted in the muscle strength of the serratus anterior. Conclusion: Our results provide novel and promising clinical evidence that patients with shoulder instability have decreased serratus anterior activation and upper trapezius overactivation, resulting in muscle imbalance. In addition, there was a significant difference between the healthy group and shoulder instability group in the serratus anterior muscle strength