During seated shoulder abduction assessment, which sequence of muscle firing is described as correct?

During seated shoulder abduction assessment, which sequence of muscle firing is described as correct?

• A. Supraspinatus, deltoid, infraspinatus, lower trapezius, contralateral quadratus lumborum
• B. Deltoid, supraspinatus, pectoralis major
• C. Infraspinatus, teres minor, supraspinatus
• D. Trapezius, latissimus dorsi, serratus anterior

Answer: (A)

Initiation of shoulder abduction begins with the supraspinatus turning on to start the movement and stabilize the humeral head in the glenoid. Without this early initiation, the deltoid’s contraction can push the head upward and away from the socket, risking impingement. Once the movement is underway, the deltoid takes over to drive the bulk of the abduction. The infraspinatus then contributes by externally rotating and helping depress and center the humeral head, further protecting the joint as the arm rises. At the same time, the lower trapezius helps position the scapula by depressing and rotating it upward, promoting proper scapulothoracic rhythm so the shoulder works smoothly as it abducts. In a seated assessment, the contralateral quadratus lumborum provides trunk stabilization, helping maintain an upright posture and a stable base from which the shoulder can move. So the best sequence reflects this pattern: supraspinatus initiates and stabilizes, deltoid powers the motion, infraspinatus provides stabilization and external rotation, lower trapezius coordinates scapular movement, and the core stabilizer (contralateral quadratus lumborum) maintains trunk stability for controlled movement.

Initiation of shoulder abduction begins with the supraspinatus turning on to start the movement and stabilize the humeral head in the glenoid. Without this early initiation, the deltoid’s contraction can push the head upward and away from the socket, risking impingement. Once the movement is underway, the deltoid takes over to drive the bulk of the abduction. The infraspinatus then contributes by externally rotating and helping depress and center the humeral head, further protecting the joint as the arm rises.

At the same time, the lower trapezius helps position the scapula by depressing and rotating it upward, promoting proper scapulothoracic rhythm so the shoulder works smoothly as it abducts. In a seated assessment, the contralateral quadratus lumborum provides trunk stabilization, helping maintain an upright posture and a stable base from which the shoulder can move.

So the best sequence reflects this pattern: supraspinatus initiates and stabilizes, deltoid powers the motion, infraspinatus provides stabilization and external rotation, lower trapezius coordinates scapular movement, and the core stabilizer (contralateral quadratus lumborum) maintains trunk stability for controlled movement.