In evaluating shoulder abduction in a seated patient, which muscle sequence is described as the correct firing order?

In evaluating shoulder abduction in a seated patient, which muscle sequence is described as the correct firing order?

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

Answer: (A)

When the arm is abducted in a seated position, the movement relies on a coordinated firing sequence to lift the arm smoothly and keep the joint stable. The supraspinatus starts the process, initiating abduction right at the beginning, especially in the first 10–15 degrees. Once the arm is ready to rise further, the deltoid takes over as the main force to raise the arm. As lifting continues, the rotator cuff, particularly the infraspinatus, helps stabilize the humeral head in the glenoid so the deltoid’s pull doesn’t push the head upward or cause impingement. To enable full range, the scapular upward rotation must occur, driven by the lower trapezius coordinating with the serratus anterior, positioning the scapula for humeral elevation. Because this is being evaluated in a seated patient, maintaining a stable trunk is also important; the contralateral quadratus lumborum helps stabilize the torso to prevent compensatory trunk movements that could limit or misdirect the shoulder motion. So the sequence—supraspinatus initiating abduction, followed by the deltoid powering the lift, with infraspinatus stabilizing the humeral head, then lower trapezius aiding scapular upward rotation, and contralateral quadratus lumborum stabilizing the trunk—fits how the body coordinates shoulder elevation most effectively. The other options mismatch the initial initiator or omit key stabilizers, making them less accurate descriptions of the firing order.

When the arm is abducted in a seated position, the movement relies on a coordinated firing sequence to lift the arm smoothly and keep the joint stable. The supraspinatus starts the process, initiating abduction right at the beginning, especially in the first 10–15 degrees. Once the arm is ready to rise further, the deltoid takes over as the main force to raise the arm.

As lifting continues, the rotator cuff, particularly the infraspinatus, helps stabilize the humeral head in the glenoid so the deltoid’s pull doesn’t push the head upward or cause impingement. To enable full range, the scapular upward rotation must occur, driven by the lower trapezius coordinating with the serratus anterior, positioning the scapula for humeral elevation.

Because this is being evaluated in a seated patient, maintaining a stable trunk is also important; the contralateral quadratus lumborum helps stabilize the torso to prevent compensatory trunk movements that could limit or misdirect the shoulder motion.

So the sequence—supraspinatus initiating abduction, followed by the deltoid powering the lift, with infraspinatus stabilizing the humeral head, then lower trapezius aiding scapular upward rotation, and contralateral quadratus lumborum stabilizing the trunk—fits how the body coordinates shoulder elevation most effectively. The other options mismatch the initial initiator or omit key stabilizers, making them less accurate descriptions of the firing order.