Which rotator cuff muscle, when contracting concentrically, causes frontal plane movement?

The supraspinatus muscle is essential for initiating movement in the shoulder, particularly concerning the frontal plane, which involves lifting the arm away from the body. When the supraspinatus contracts concentrically, it plays a crucial role in abduction of the arm, effectively raising it laterally in the frontal plane.

This movement is fundamental in various activities that require lifting the arm, such as reaching overhead or performing tasks that involve lateral arm motion. The supraspinatus works in conjunction with the deltoid muscle during this process, particularly in the first 15 degrees of abduction before the deltoid takes over.

While the other rotator cuff muscles—subscapularis, infraspinatus, and teres minor—have important roles in shoulder stability and movement, they do not primarily facilitate abduction in the frontal plane. Instead, the subscapularis primarily assists with internal rotation, while the infraspinatus and teres minor are involved in external rotation of the shoulder joint. Thus, the unique action of the supraspinatus in facilitating frontal plane movement through abduction makes it the correct choice in this context.