Shoulder Internal Rotation: Muscles Stretched, Importance, and Stretching

What muscles does shoulder internal rotation stretch?

Shoulder internal rotation primarily stretches the muscles responsible for external rotation of the humerus at the glenohumeral joint, most notably the infraspinatus and teres minor, along with the posterior fibers of the deltoid and the posterior joint capsule.

Understanding Shoulder Internal Rotation

Shoulder internal rotation is a fundamental movement of the glenohumeral (shoulder) joint, where the humerus (upper arm bone) rotates medially (inward) towards the body's midline. This action occurs around a vertical axis, bringing the forearm and hand across the front of the body if the elbow is bent at 90 degrees. While many muscles work to achieve internal rotation (e.g., subscapularis, pectoralis major, latissimus dorsi, teres major, anterior deltoid), the muscles that are stretched during this movement are their functional antagonists: the external rotators.

Primary Muscles Stretched by Shoulder Internal Rotation

When the shoulder is internally rotated, the muscles that oppose this movement—the external rotators—are lengthened. These are the primary targets for a shoulder internal rotation stretch:

• Infraspinatus: This large, thick muscle occupies most of the posterior surface of the scapula (shoulder blade). As one of the four rotator cuff muscles, its primary action is external rotation of the humerus. When the arm is internally rotated, the infraspinatus is put on stretch.
• Teres Minor: A smaller rotator cuff muscle located inferior to the infraspinatus, the teres minor also functions as a primary external rotator of the humerus. Like the infraspinatus, it is lengthened during internal rotation.

Accessory Muscles and Structures Stretched

Beyond the primary external rotators, other muscles and structures may also experience a stretch during shoulder internal rotation, depending on the specific position of the arm and the overall movement:

• Posterior Deltoid: The posterior fibers of the deltoid muscle, which forms the rounded contour of the shoulder, assist in external rotation and extension of the humerus. When the arm is internally rotated, particularly if also flexed or abducted, the posterior deltoid can undergo significant stretch.
• Posterior Shoulder Capsule: While not a muscle, the posterior glenohumeral joint capsule is a crucial ligamentous structure that can become tight, limiting internal rotation. Stretching into internal rotation often targets the flexibility of this capsule, which is essential for full range of motion and shoulder health.
• Other Posterior Shoulder Musculature: While less direct, other muscles of the posterior shoulder and upper back, such as parts of the trapezius or rhomboids, may experience secondary stretch if the internal rotation movement is combined with other actions (e.g., adduction across the body).

Importance of Stretching Shoulder Internal Rotators

Maintaining flexibility in the shoulder's external rotators and posterior capsule is critical for overall shoulder health and function. Tightness in these areas can lead to:

• Reduced Range of Motion: Limiting the ability to perform activities requiring full shoulder internal rotation, such as reaching behind the back.
• Impingement Syndrome: Imbalances in muscle length and strength around the shoulder can alter glenohumeral kinematics, potentially contributing to subacromial impingement.
• Postural Deviations: Chronic tightness can pull the shoulder into an externally rotated or protracted position, affecting overall posture.
• Increased Risk of Injury: Especially in overhead athletes (e.g., baseball pitchers, tennis players), adequate internal rotation range of motion is crucial for preventing injuries during the follow-through phase of throwing or striking.

How to Safely Stretch Shoulder Internal Rotators

When stretching, always prioritize safety and controlled movements. Focus on a gentle, sustained stretch rather than bouncing or forcing the movement.

• Controlled Movement: Slowly move into the stretch until you feel a gentle pull, not pain.
• Hold Duration: Hold the stretch for 20-30 seconds, repeating 2-3 times.
• Breathing: Breathe deeply and steadily throughout the stretch to promote relaxation.
• Consistency: Regular stretching yields the best results for improving flexibility.
• Listen to Your Body: Never stretch into pain. If you experience sharp or radiating pain, stop immediately.

Common stretches that target these muscles include the "sleeper stretch" (lying on your side, internally rotating the arm with assistance) and various cross-body internal rotation stretches.

When to Consult a Professional

While stretching can be beneficial, persistent pain, significant loss of range of motion, or an inability to perform daily tasks should prompt a consultation with a healthcare professional. A physical therapist, kinesiologist, or sports medicine physician can accurately diagnose the cause of your limitations and recommend a tailored program of exercises and stretches.

Conclusion

Understanding the specific muscles stretched during shoulder internal rotation—primarily the infraspinatus, teres minor, and posterior deltoid, along with the posterior joint capsule—is key to effectively addressing tightness and improving shoulder mobility. Incorporating targeted stretches for these structures can enhance athletic performance, prevent injury, and contribute to overall shoulder health and functional movement.