Effect of Scapular Stabilizer Muscles Strength on Scapular Position

Abstract

Background: Maintaining scapular mechanics is important for upper extremity functionality and posture. Determining the extent to which the scapular stabilizer muscles affect the scapular position may guide the creation of an exercise program for people with scapular dyskinesis. Hypothesis: The serratus anterior (SA), upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) muscles play different roles on scapular position when humeral elevation increase. Study Design: Cross-sectional study. Level of Evidence: Level 4. Methods: A total of 70 women aged 40 to 65 years (mean age, 49 ± 7 years) who met the inclusion criteria were included in the study. Isometric muscle strength of the SA, UT, MT, and LT was evaluated with a handheld dynamometer. For assessment of scapular position, the lateral scapular slide test (LSST) was used. Multiple stepwise regression analysis was used to evaluate scapular parameters. Results: There were positive and statistically significant correlations between the isometric muscle strength of the SA, UT, MT, and LT muscles and the values at different humerus positions in the LSST ( P < 0.05). The UT and SA muscles greatly affected the changes in the position of the inferior region of the scapula ( R2 > 24.5%). The LT (11.3%) in neutral position, MT (25.4%) with arm abducted at 45°, and SA (34.5%) with arm abducted 90° had a major effect on the changes in the mediolateral position of the scapula. Conclusion: While the LT muscle affects the mediolateral position of the scapula to a large extent, the strength of the MT and SA muscles becomes effective as the shoulder elevation increases. SA and UT muscle strength have a greater effect on the position of the inferior region of the scapula. Clinical Relevance: Dyskinesis can be observed at different levels of the scapula; therefore, it is important to determine at which level the dyskinesis is more prominent for each individual and consequently to form a personalized exercise program to increase function and control dyskinesis.