Shoulder pain during throwing is common in sports requiring repetitive overhead motion, such as baseball, tennis, and javelin. The shoulder joint is designed for extreme mobility, but this flexibility makes it susceptible to injury under the intense forces generated by a throw. Understanding the biomechanical phases and the structures under stress helps identify the source of the pain. The repetitive, high-velocity movement often causes accumulated microtrauma, leading to pain and functional limitation.
The Mechanics of Overhead Throwing
The overhead throwing motion is a highly coordinated, full-body movement that generates some of the fastest angular velocities in the human body. The shoulder must withstand incredible forces as it transfers energy from the legs and trunk to the hand. This motion is broken down into distinct phases, three of which place the shoulder under maximum strain.
The late cocking phase is marked by the shoulder reaching maximum external rotation, often nearing 180 degrees, a position of extreme stress. During this phase, soft tissues at the front of the shoulder are stretched, and rotator cuff tendons at the back can become pinched, known as internal impingement. This extreme external rotation is a major precursor to several common throwing injuries.
The acceleration phase is explosive, characterized by a rapid burst of internal rotation, which can reach rotational speeds of up to 7,000 degrees per second. This speed generates massive kinetic energy, placing high shear forces on the anterior and superior joint structures. The acceleration phase concludes at ball release.
The deceleration phase follows ball release and is the most physically demanding phase for the shoulder joint. The arm must be forcefully braked from its maximum velocity by the eccentric contraction of the rotator cuff muscles, particularly the infraspinatus and teres minor. This braking action creates a powerful distraction force that pulls the arm away from the socket, stressing the posterior shoulder structures and the biceps-labral complex.
Specific Injuries Linked to Throwing Pain
The repetitive, high-force nature of throwing leads to specific patterns of injury in the shoulder’s delicate anatomy. The most common anatomical structures that fail under this stress include the rotator cuff, the glenoid labrum, and the biceps tendon.
Rotator Cuff Issues
The rotator cuff tendons stabilize the humeral head within the shallow socket and are frequent sites of injury in throwers. Rotator cuff tendinopathy is irritation and inflammation of these tendons, often presenting as diffuse pain that radiates down the side of the arm. Pain may be present during throwing, at rest, or at night.
Chronic irritation can progress to partial tears, most commonly affecting the undersurface of the supraspinatus tendon. These tears often result from repetitive internal impingement during the late cocking phase. The pain arises because fatigued or damaged tendons can no longer maintain the humeral head’s stability during the throw, leading to instability and further pinching.
Glenoid Labrum Tears (SLAP Lesions)
The glenoid labrum is a rim of tough, fibrous tissue that deepens the shoulder socket and anchors the long head of the biceps tendon. A common injury in throwers is a Superior Labrum Anterior to Posterior (SLAP) tear, which involves a tear in the upper portion of this rim.
This tear often results from the “peel-back” mechanism, where the biceps tendon twists and pulls the labrum away from the bone as the arm is forced into maximum external rotation during the late cocking phase. The high eccentric load on the biceps tendon during deceleration is also a factor. Symptoms include deep, internal pain, clicking, popping, or a sensation of instability.
Impingement Syndrome
Internal impingement occurs when the rotator cuff tendons and the labrum are pinched between the head of the humerus and the back of the glenoid socket. This mechanical contact happens when the arm is abducted and maximally externally rotated during the cocking phase. It causes posterior shoulder pain and is often associated with partial rotator cuff tears and SLAP lesions. This condition differs from external (subacromial) impingement, which involves the rotator cuff being pinched against the bony arch above it, and is less common in young, high-velocity throwers.
Factors That Increase Throwing Injury Risk
While the act of throwing itself imposes high stress, certain underlying physical deficits and behaviors significantly elevate the risk of injury. These factors compromise the body’s ability to manage the immense forces transmitted through the shoulder.
Poor conditioning of the scapular stabilizers (muscles supporting the shoulder blade) is a major contributor to throwing pain. Weakness in these muscles disrupts the smooth movement of the scapula, leading to altered shoulder mechanics, known as scapular dyskinesis. This improper movement forces the glenohumeral joint to compensate, increasing strain on the cuff and labrum.
Throwing with fatigue is one of the most significant and preventable risk factors for serious injury. Athletes who pitch through arm fatigue have a higher likelihood of requiring elbow or shoulder surgery. Fatigue leads to subtle changes in throwing technique and timing, which quickly overload the stabilizing structures.
A common physical adaptation in throwers is a loss of internal rotation range of motion in the throwing shoulder, known as Glenohumeral Internal Rotation Deficit (GIRD). This tightness in the posterior capsule shifts the center of rotation, which contributes to the harmful impingement of the rotator cuff and labrum during the throwing motion. Addressing this deficit is essential for injury prevention.
When to Seek Help and Initial Care
When shoulder pain begins during throwing, the immediate and most important step is to stop throwing and rest the arm. Continuing to throw through pain, especially a sharp pain, significantly increases the risk of a minor issue becoming a severe, chronic injury.
For initial, mild soreness, self-care steps can provide relief. Applying ice to the painful area for 15 to 20 minutes several times a day can help reduce inflammation and pain. Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) may also be used to manage discomfort.
Certain signs, often referred to as red flags, indicate the need for prompt medical evaluation by an orthopedic specialist or physical therapist. You should seek immediate attention if you experience a sudden, sharp, or intense pain accompanied by a sensation of a “pop” or tear. Other concerning symptoms include:
- Inability to lift or move the arm normally.
- Visible deformity or swelling around the joint.
- Pain that persists for more than 48 hours after stopping the activity and resting.
A specialist can perform a thorough evaluation and recommend a structured rehabilitation program. This program focuses on restoring range of motion, strength, and proper throwing mechanics for a safe return to overhead activity.