Association of Scapular Acromion-table Distance with Upper Quarter Y-balance Test and Trapezius Muscle Activity Patterns

Objective: This study investigated whether the acromion-table distance is associated with trapezius activity patterns during shoulder movements and the upper quarter Y-balance test (UQYBT). Additionally, it was to determine the correlation between upper, middle, and lower trapezius muscle activity. Design: Cross-sectional study Methods: Twenty-eight healthy young males participated in this study. Outcome measures included: (1) acromion-to-table distance, which assesses the scapular position, (2) trapezius muscle activity during shoulder flexion and abduction, and (3) the UQYBT, a measure of upper extremity function measured. Results: A significant negative correlation was observed between the acromion-table distance and the inferior-lateral direction reach distance of UQYBT (r＝-0.499 and p＝0.007). There were negative correlations between the upper and lower trapezius during shoulder flexion (r＝-0.901, p < 0.001) and abduction (r＝-0.661, p < 0.001), respectively. There was also a negative correlation between the upper and middle trapezius during shoulder abduction (r＝-0.466, p＝0.012). Conclusions: The acromion-table distance was related to the UQYBT. Anterior tilt of the scapula and limited range of motion of the shoulder may occur as the acromion-table distance increases. In addition, the acromion-table distance reflects the pectoralis minor muscle shortening, suggesting that the scapula position or the pectoralis minor shortening may influence the upper limb function. Therefore, these factors should be considered when assessing upper limb function using the UQYBT.