Understanding the Posterior Shoulder: Anatomy of Muscles, Bones, and Tendons

The posterior shoulder plays a crucial role in upper body strength, posture, and injury prevention. While often overshadowed by the more visible chest and front deltoid muscles, the rear portion of the shoulder complex is essential for balanced development and long-term joint health. Let’s explore the detailed anatomy of the posterior shoulder, from muscles to bones and tendons, and why it matters in both athletic performance and daily function.

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Posterior Shoulder Muscles Anatomy

The primary muscles of the posterior shoulder include the posterior deltoid, infraspinatus, teres minor, and part of the trapezius and rhomboids. Each plays a specific role in scapular stabilization and external rotation of the humerus:

• Posterior Deltoid: This muscle sits on the rear cap of the shoulder and contributes to horizontal abduction and shoulder extension. It’s often undertrained in comparison to the anterior deltoid.

• Infraspinatus: A key rotator cuff muscle located beneath the scapular spine. It externally rotates the arm and stabilizes the shoulder during dynamic movements.

• Teres Minor: Working closely with the infraspinatus, it also aids in external rotation and helps keep the humeral head properly aligned in the glenoid cavity.

• Trapezius (middle and lower fibers) and rhomboids: These muscles retract and stabilize the scapula, providing a solid foundation for shoulder movement.

Neglecting these muscles can result in poor posture, shoulder impingement, and reduced overhead strength. In training programs, rear delt flys, face pulls, and external rotation exercises are often used to target this region.

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Posterior Shoulder Bones

The bony structure of the posterior shoulder includes:

• Scapula (shoulder blade): This flat, triangular bone sits against the ribcage and provides the foundation for multiple muscle attachments. Notably, the spine of the scapula, which you can feel along the upper back, divides the infraspinatus and supraspinatus areas.

• Humerus: The upper arm bone articulates with the scapula at the glenohumeral joint. The greater tubercle of the humerus is where several rotator cuff tendons attach.

• Clavicle: While mostly anterior, its lateral end connects to the acromion (part of the scapula), impacting shoulder mechanics.

Proper function of these bones depends on the coordinated action of the surrounding muscles and tendons. When bone alignment or movement patterns are off, compensations and injuries often follow.

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Posterior Shoulder Tendon Anatomy

Tendons in the posterior shoulder connect the muscles to the bones, acting as stabilizers and force transmitters. The most critical among these include:

• Infraspinatus tendon: Attaches the infraspinatus muscle to the greater tubercle of the humerus. It’s commonly affected in rotator cuff injuries.

• Teres minor tendon: Also attaches to the greater tubercle, helping in external rotation and shoulder stability.

• Posterior deltoid tendon: Connects the posterior deltoid muscle to the deltoid tuberosity on the humerus. Though less commonly injured, it can suffer strain in high-volume training or poor posture scenarios.

Understanding the tendon structure is especially important for those recovering from shoulder injuries or undergoing postural correction. These tendons are more vulnerable to overuse if shoulder mechanics are poor or if antagonist muscles (like the pecs) are overly dominant.

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A Personal Note: The Wake-Up Call That Shifted My Training

Several years ago, I began experiencing sharp discomfort near the back of my shoulder during overhead presses. Like many lifters, I was guilty of overtraining the front delts and pecs while giving little attention to my rear delts or external rotators. After a physical therapist identified significant weakness in my posterior chain, I committed to a rehab program focused on face pulls, band external rotations, and prone Y-raises. Within weeks, not only did the pain subside, but my overall shoulder strength improved. That experience reshaped how I structure upper-body workouts—for both myself and my clients.