Relationship between performance of selected scapular muscles and scapular abduction in standing subjects.

The purpose of this study was to examine the relationship between muscular forces generated by the middle trapezius and pectoralis minor muscles and the position of the scapula in relaxed standing. The muscular forces of 60 subjects were measured in standard manual muscle testing positions with a hand-held dynamometer. Scapular abduction in standing was measured with a tape measure. Each measurement was taken twice, and the measurements were shown to be reliable. The correlation between scapular abduction and middle trapezius muscle force was .20. The correlation between scapular abduction and pectoralis minor muscle force was .14. The correlation between scapular abduction and a ratio of middle trapezius muscle force to pectoralis minor muscle force was .01. The results indicate that no relationship exists between the position of the scapula in standing subjects and the muscular force produced by the middle trapezius and pectoralis minor muscles. Clinical practices based on an assumed relationship between these variables (eg, the practice of using middle trapezius muscle strengthening exercises to correct a forward shoulder position) should be reexamined in light of these findings.