Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

Which muscle is primarily responsible for the first 30 degrees of abduction?

1. Infraspinatus

2. Supraspinatus

3. Teres minor

4. Subscapularis

The correct answer is: Supraspinatus

The supraspinatus muscle is primarily responsible for the first 30 degrees of abduction of the arm. This muscle is one of the four rotator cuff muscles and plays a critical role in initiating the abduction movement. While other muscles, such as the deltoid, are indeed involved in abduction, the supraspinatus is essential during the initial phase. During the first 30 degrees of abduction, the supraspinatus provides the necessary torque and stabilization to the shoulder joint, allowing for a smooth and controlled movement. Its position above the shoulder joint and angle of contraction makes it particularly effective for this initial segment of abduction. As the arm continues to move past 30 degrees, the deltoid muscle takes over as the primary mover for abduction. Understanding the specific roles of these muscles is essential for comprehending shoulder mechanics and the functional anatomy involved in arm movements.