Whether you are reaching the finish line of a 400m freestyle or locking out a heavy overhead press, your shoulder is performing one of the most complex mechanical feats in the human body. However, for many athletes, this “overhead” zone is where a sharp, pinching pain begins to settle in.
In the clinical world, we often refer to this as Subacromial Impingement Syndrome (SIS)—or more accurately in modern literature, Rotator Cuff-Related Shoulder Pain (RCRSP). Here is the science behind why your favorite activities might be “pinching” your progress.
The Anatomy of the “Pinch”
The shoulder is a ball-and-socket joint, but unlike the deep socket of the hip, the shoulder’s socket (the glenoid) is shallow. To allow for massive range of motion, the “ceiling” of your shoulder is formed by a bony arch called the acromion.
The narrow gap between the top of your arm bone (humerus) and this bony ceiling is the subacromial space. This space is prime real estate, packed with:
- The Rotator Cuff Tendons: Specifically the supraspinatus, which helps lift your arm.
- The Subacromial Bursa: A fluid-filled sac that acts as a lubricating cushion.
Why Swimming and Gym Training are High-Risk
Impingement isn’t usually caused by a single injury; it’s a “space management” issue. When you raise your arm overhead, the subacromial space naturally narrows. In a healthy shoulder, the mechanics are tuned to keep this gap open. In impingement, that gap collapses.
1. The Swimmer’s “Catch” and Internal Rotation
In freestyle swimming, the “catch” phase requires high-force internal rotation while the arm is fully extended overhead. Research suggests that competitive swimmers can perform up to 30,000 strokes per week (Peak Physio, 2026). This repetitive “closing of the gap” can lead to:
- Fatigue-Induced Scapular Dyskinesis: As your back muscles (serratus anterior and traps) tire, your shoulder blade stops rotating upward correctly, effectively lowering the “ceiling” onto the tendons.
- Forward Shoulder Posture: Tightness in the pectorals from hours in the pool pulls the acromion forward and down, further reducing available space.
2. The Gym: Heavy Loading and “The Arc”
In the gym, the risk comes from loading that narrow space. During an overhead press or lateral raise, the “painful arc” usually occurs between 60° and 120° of elevation.
- Lack of Thoracic Extension: If your mid-back is stiff, your shoulder has to “make up” the extra range to get the bar overhead. This forced range often tilts the humerus directly into the acromion.
- Rotator Cuff Weakness: The cuff’s job is to pull the “ball” down into the socket. If the cuff is weak, the larger deltoid muscle pulls the ball upward, “impinging” the structures against the bone (AAOS, 2026).
Is it Structural or Functional?
Physiotherapy traditionally categorizes impingement into two types:
| Type | Cause | Common Example |
| Primary (Structural) | Physical narrowing due to bone spurs or acromion shape. | Older athletes or those with osteoarthritis. |
| Secondary (Functional) | The space is fine, but the movement is wrong. | Swimmers with weak scapular stabilizers or gym-goers with poor form. |
Clinical Note: Modern research (Cureus, 2022) suggests we move away from seeing the shoulder as “fragile” or “pinched.” Instead, we view it as a load tolerance issue. The pain is often a “check engine light” telling us the tendons aren’t strong enough yet for the volume of work you’re asking them to do.
How We Bridge the Gap
Recovery isn’t just about “resting” the shoulder; it’s about optimizing the space. Our physiotherapy approach focuses on three pillars:
1. Load Management: The ‘Quiet’ Phase.
We don’t always stop you from training. We modify. For swimmers, this might mean using fins to reduce shoulder pull. For lifters, switching to a landmine press or “scaption” (30° forward) to open the joint.
2.Scapular Retraining: Opening the Space.
We strengthen the “upward rotators” of the shoulder blade (Lower Traps and Serratus Anterior). This ensures the “ceiling” (acromion) moves out of the way as the arm goes up.
3.Rotator Cuff Conditioning: Centering the Joint.
Specific exercises like “Full Can” raises and external rotations teach the rotator cuff to keep the humeral head centered in the socket, preventing it from migrating upward into the subacromial structures.
References
- American Academy of Orthopaedic Surgeons (AAOS). (2026). Rotator Cuff and Shoulder Conditioning Program.
- Cureus Journal of Medical Science. (2022). Subacromial Impingement Syndrome: A Systematic Review.
- Movement for Life Physiotherapy. (2026). The Biomechanics of Swimmer’s Shoulder.