The effect of arm position on stretching of the supraspinatus, infraspinatus, and posterior portion of deltoid muscles: a cadaveric study.

BACKGROUND

The stretching of the supraspinatus and infraspinatus muscles is important to prevent shoulder injuries. Although several authors have advocated various stretching techniques, a general opinion has not been reached owing to the lack of quantitative analysis.

METHODS

Nine fresh cadaveric shoulders were used to measure the strain on the supraspinatus, the middle and inferior portions of the infraspinatus, and the posterior portion of the deltoid muscles during eleven arm positions. The strain on the muscles was measured by precise displacement sensors attached to the center of each muscle belly.

FINDINGS

In case of the supraspinatus muscle, abduction at extension showed significantly larger strain than that in the neutral position (P < 0.05). Internal rotation at extension showed significantly larger strain in the middle portions of the infraspinatus (P < 0.05). Internal rotation at 30 degrees and 60 degrees elevation as well as extension showed significantly larger strain in the inferior portion of the infraspinatus (P<0.05). Adduction at 60 degrees elevation did not show large strain in the infraspinatus muscle; however, significantly larger strain was observed in the posterior portion of the deltoid muscle.

INTERPRETATION

Shoulder stretching techniques that are based on these experimental data can enhance the selective stretching of the corresponding muscles. Application of these techniques is considered to be useful for the prevention and treatment of shoulder injuries.