Right shoulder pain may be the most common injury in all swimming. Having worked with hundreds of swimmers over the last 13 years, I have seen the right shoulder injured more than any other area, including the left shoulder. There are theories about its injury prevalence. More people being right-handed or swimmers breathing more on their dominant side (which is likely to be the right) come to mind. But, is there more to it than that?
Asymmetrical Anatomy
If we take a look at how the human body is structured, it's filled with asymmetry. The right diaphragm is roughly three times thicker and stronger than the left, and it attaches further down the lumbar spine. There are three lobes of lung on the right side compared to two on the left. The heart is more on the left side. The liver is on the right side. While there is more asymmetry above and below the listed areas, you get the point. And to think this isn't going to affect how the body moves and functions would be naive.
This is going to position you more on your right side. You will typically prefer to stand on your right leg. It feels more comfortable there and it's easier to breathe. You’ll find it's likely easier to balance on your right leg instead of your left.
Impact on the Right Shoulder
This means the right shoulder is usually going to sit lower than the left and be positioned more into internal rotation. It may even wing or start to lift off of the rib cage. The right abdominal wall, latissimus dorsi, and pec minor are likely to all be 'on' to keep us on the right side. You may also see the intercostals (muscles between ribs) get more contracted on the right side.
The pec and lat both are internal rotators of the shoulder. Dominance of these two muscles in normal everyday function can position the right shoulder blade to tilt anteriorly and downwardly rotate. With them already internally rotating the shoulder, you'll have less internal rotation. This can inhibit two key muscles for shoulder health written about HERE, the serratus anterior and subscapularis.
To summarize, the serratus anterior assists in keeping the shoulder blade flush to the rib cage. It is also a scapular protractor and upward rotator of the scapula in overhead movements. The subscapularis works to provide anterior stability to the shoulder joint and internally rotates the shoulder.
Less anterior stability of the shoulder joint and limited movement of the shoulder blade can mean anterior and superior migration of the humeral head. This is called impingement, and it can be quite painful.
Goals to Reduce Right Shoulder Pain
To reduce pain and improve function, the right shoulder blade needs to be in a better position. Initially, this means facilitating the right lower trapezius. This will tilt the shoulder blade back, which can increase some of the subacromial space and give the rotator cuff more freedom to move.
Follow that up by strengthening the serratus anterior. This builds better scapular upward rotation and provides adequate tension to keep the scapula flush to the rib cage.
Reducing asymmetry completely isn't the goal nor is it possible. But, by addressing these two muscles, you can reduce pain significantly and get back in the water to train.