The shoulder is the most mobile joint in the human body, allowing for the wide range of motion necessary for overhead activities like throwing. This mobility comes at the cost of stability, making the joint susceptible to injury from repetitive, high-velocity forces. Throwing places significant stress on the structures that stabilize the shoulder. For overhead athletes, this repetitive strain often leads to breakdown in the muscles, tendons, ligaments, or cartilage, resulting in pain that impacts performance.
The Biomechanics of Painful Throwing
The act of throwing is a complex, full-body motion broken down into distinct phases, each placing unique strain on the shoulder joint. The sequence of body segments moving to generate force begins in the lower body, but the shoulder must absorb and transmit the final energy. If the sequence is mistimed or if the lower body is weak, excessive force is transferred directly to the shoulder, increasing the risk of injury.
The initial phase, known as the cocking phase, involves the arm moving backward into maximum external rotation. During this stage, the anterior (front) structures of the shoulder, including the ligaments and joint capsule, are stretched to their limit. This stretching can lead to micro-instability and place the rotator cuff tendons at the back of the shoulder at risk of being pinched, a phenomenon known as internal impingement.
The acceleration phase is the high-velocity, propulsive movement where the arm rapidly moves forward until ball release. During this phase, the rotator cuff muscles contract powerfully to help stabilize the joint and generate speed, making them vulnerable to overuse and fatigue. This rapid, forceful motion can generate high throwing shoulder distraction forces, which can place significant stress on structures like the biceps tendon near its anchor point.
Following ball release is the deceleration phase, which requires the shoulder to dissipate the energy generated in a fraction of a second. The posterior (back) muscles of the rotator cuff, specifically the infraspinatus and teres minor, work eccentrically to act as the arm’s brake. This braking action creates high distractive forces, which may be equal to the thrower’s body weight, putting strain on the posterior capsule and increasing the chance of injury to the tendons and ligaments.
Soft Tissue Injuries: Rotator Cuff and Tendon Issues
The most frequent causes of shoulder pain in throwers involve the soft tissues, primarily due to cumulative microtrauma and overuse. The rotator cuff, a group of four muscles and their tendons, functions as the dynamic stabilizer of the shoulder, keeping the head of the humerus centered in the socket. When these muscles are overworked or fatigued, the tendons can become inflamed, a condition known as rotator cuff tendinopathy or tendinitis.
This irritation often results in a dull, aching pain that worsens during throwing and may persist even while resting, sometimes disturbing sleep. Shoulder impingement syndrome occurs when the rotator cuff tendons get compressed as they pass through the narrow space beneath the acromion, the bony roof of the shoulder. Repetitive overhead motion can cause the tendons to rub against the bone, leading to inflammation and, if left untreated, eventual fraying or tearing of the tendon fibers.
The tendon of the long head of the biceps travels through the shoulder joint, attaching to the upper part of the socket. Repetitive throwing can cause this tendon to become inflamed, resulting in biceps tendinitis, which typically causes pain in the front of the shoulder. Chronic inflammation can weaken the tendon, potentially leading to a partial or complete tear, sometimes accompanied by a sudden, sharp pain or a popping sensation.
Joint Structure Injuries: Labrum and Instability
Injuries to the joint’s static stabilizers—the cartilage and ligaments—represent a more structural failure, often resulting in sharp pain or a feeling of mechanical dysfunction. The labrum is a ring of tough fibrocartilage that lines the glenoid, the shoulder socket, deepening the cup to hold the arm bone in place. In throwers, the most common type of injury is a SLAP tear, which stands for Superior Labrum Anterior to Posterior.
This specific tear occurs at the top of the labrum where the long head of the biceps tendon attaches. SLAP tears are caused by the tensile forces placed on the biceps anchor during the late cocking and early acceleration phases of throwing. Symptoms often include deep, aching pain, a noticeable loss of throwing velocity, and mechanical symptoms like clicking, popping, or catching sensations within the joint.
The repetitive, forceful motions of throwing can also lead to shoulder instability, where the static structures become stretched. Stretching of the ligaments and joint capsule over time results in increased laxity. This laxity can cause the head of the humerus to shift out of the center of the socket, potentially leading to subluxation, where the joint partially slips out of place. Instability is often perceived as the shoulder feeling loose, sometimes accompanied by a loss of strength and a decline in throwing performance.
Immediate Care and Seeking Diagnosis
When shoulder pain begins during throwing, the immediate priority is to modify activity to prevent further structural damage. For minor aches and inflammation, at-home care involves the RICE principles: rest, applying ice, and using over-the-counter anti-inflammatory medications like ibuprofen. Applying ice packs to the painful area for 15 to 20 minutes several times a day can help reduce swelling and discomfort.
Seeking professional help becomes necessary if the pain is persistent or if specific red flags appear. You should schedule an office visit if the pain continues for several weeks without improvement, if you notice swelling or warmth around the joint, or if movement becomes increasingly difficult. These symptoms suggest an underlying issue like chronic tendinitis, bursitis, or a developing tear that requires formal diagnosis.
Certain symptoms necessitate immediate medical attention, potentially requiring a trip to an urgent care facility or emergency room. These red flags include a sudden onset of severe pain, a visible deformity of the shoulder joint, or a complete inability to move the arm. Numbness, tingling, or weakness in the arm and hand are also serious indicators, as they may signal nerve compression or severe structural damage. A definitive diagnosis, often confirmed by imaging like an MRI, will determine the next steps, which may range from physical therapy to consultation with a specialist.