Effect of Scapular Stabilizer Muscles Strength on Scapular Position

Area of Science:

• Biomechanics
• Kinesiology
• Musculoskeletal health

Background:

• Scapular mechanics are crucial for upper extremity function and posture.
• Scapular dyskinesis can impair shoulder function and lead to pain.
• Identifying the role of scapular stabilizer muscles is key for targeted interventions.

Purpose of the Study:

• To investigate the relationship between the isometric strength of key scapular stabilizer muscles and scapular position.
• To determine which scapular muscles most significantly affect scapular positioning at various humeral elevations.
• To inform the development of exercise programs for individuals with scapular dyskinesis.

Main Methods:

• Cross-sectional study involving 70 women aged 40-65.
• Isometric muscle strength of serratus anterior (SA), upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) measured using a handheld dynamometer.
• Scapular position assessed using the lateral scapular slide test (LSST); data analyzed with multiple stepwise regression.

Main Results:

• Significant positive correlations were found between muscle strength of SA, UT, MT, and LT and scapular position across different humeral elevations.
• UT and SA strength strongly influenced the inferior scapular region's position (R² > 24.5%).
• LT, MT, and SA showed the most significant effects on mediolateral scapular position at neutral, 45°, and 90° arm abduction, respectively.

Conclusions:

• Scapular muscle strength is directly related to scapular positioning.
• The influence of specific muscles (LT, MT, SA) on scapular position varies with the degree of shoulder elevation.
• SA and UT strength are particularly important for controlling the inferior scapular region's position.