Shoulder Pain in Swimmers and Paddleboarders: Why the Same Reach Wears Down Differently on Each Side

You swim laps or paddle out most mornings, repeating the same reach hundreds of times in a session and thousands of times over a month.

When pain finally appears, it may show up on only one side. Your stroke looks symmetrical and may have felt balanced for years, yet one shoulder is no longer tolerating the same workload as the other.

The shoulder does not work alone. The rotator cuff, shoulder blade muscles, upper back and surrounding structures coordinate to position and control the arm during every reach.

If one side contributes differently, even slightly, two strokes that look almost identical can place very different demands on each shoulder.

Why the Reach Can Look the Same While the Load Is Different

Small differences in shoulder blade control or upper-back rotation can be difficult to see from the outside.

One shoulder blade may rotate and stabilise effectively while the other moves slightly differently. Likewise, reduced thoracic rotation on one side may require the shoulder to contribute more movement to complete the same reach.

The visible stroke can remain similar while the movement strategy underneath it changes.

The American Academy of Orthopaedic Surgeons explains that repetitive overhead movement in swimming can contribute to shoulder irritation and that factors such as muscle fatigue and altered mechanics can play a role.

Why Volume Turns a Small Difference Into a Bigger Problem

A small movement difference during a single stroke may cause no noticeable problem.

Repeat that movement hundreds of times in one session, several times each week, and the cumulative demand becomes much more significant.

This helps explain why swimming and paddling shoulder problems can develop gradually rather than beginning with one obvious injury.

The shoulder may tolerate the pattern for weeks or months before increasing training volume, longer sessions or reduced recovery finally exposes the difference between the two sides.

What May Actually Be Different From Side to Side?

A useful assessment looks beyond the painful shoulder itself.

How well does each shoulder blade control the arm overhead? Does the thoracic spine rotate equally in both directions? Does one side rely more heavily on the shoulder joint to complete the reach?

Strength, mobility, timing and control can all contribute to how effectively each side manages repeated overhead movement.

At Abbysan, a Foundation Assessment can examine these side-to-side differences and identify where the movement chain may be distributing load unevenly.

Why Strengthening the Sore Shoulder Alone May Not Be Enough

Strengthening can be an important part of recovery, but it works best when it matches what the assessment actually finds.

If reduced upper-back rotation or altered shoulder blade control is contributing to the problem, strengthening only the painful area may leave the original movement pattern unchanged.

Once swimming or paddling volume increases again, the same side may begin absorbing the same additional demand.

The goal is therefore not simply to make the painful shoulder stronger. It is to understand why that shoulder has been carrying more of the workload in the first place.

Find the Difference Your Stroke Does Not Show

If one shoulder repeatedly takes the toll of a movement that appears symmetrical, the important difference may be happening beneath what you can see.

Assessing shoulder blade control, thoracic rotation, mobility and load tolerance can provide a clearer picture of how each side is actually performing.

Once those differences are identified, training can focus on what your body specifically needs before the next increase in swimming or paddling volume.