Swimmer's Shoulder: Why It Happens, How We Assess It, and How We Treat It

Shoulder pain is the most common complaint in competitive swimming — and the most commonly normalised. Somewhere between 40% and 91% of swimmers will experience it across a career, it costs more lost training time than any other injury in the sport, and most club swimmers believe it is simply part of swimming. In one survey of high-school club swimmers, as many as 73% reported using pain medication in order to keep training.

It shouldn't be that way. This article walks through what swimmer's shoulder actually is, what the evidence says causes it, how we assess it at Step Ahead, and how we treat it.

What swimmer's shoulder actually is

"Swimmer's shoulder" is an umbrella term rather than a diagnosis. It describes persistent shoulder pain driven by repetitive load around the subacromial region.

Most often it involves the rotator cuff tendons — supraspinatus and subscapularis — along with the subacromial bursa and the long head of biceps. Importantly, testing and imaging correlate poorly with exactly which of these structures is the painful source. Thankfully, the treatment and management of each are broadly similar, so the useful question is rarely "which structure is it?" but "what is loading this region, and how much?"

It's a recovery problem more often than a training problem

Here is the part that changes how you manage it.

In elite swimmers, the supraspinatus and subscapularis tendons normally increase in size by around 5% after a single session, and by up to 10% across a training week. That swelling is a completely normal adaptive response to training. It is not injury, and it is not something to avoid.

The problem is reloading a tendon before it has returned to baseline.

• After a high-volume session, tendon thickness settles within around 6 hours
• After a high-intensity session, it can take 24 hours
• Stack intensity on intensity, and the tendon never gets back to the start line

That is why swimmer's shoulder is far more often a recovery problem than a training problem. The volume itself is rarely the villain; the spacing of it usually is.

The shoulder is also doing an enormous amount of work. Up to 90% of freestyle propulsion comes from the upper limbs, and elite swimmers complete well over a million strokes a year. A dropped elbow or a crossover entry adds drag, and the body compensates by loading the shoulder harder to hold speed. Inefficient mechanics quietly become an injury problem.

It is a continuum, and the early signs matter

Swimmer's shoulder rarely arrives all at once. It usually starts small:

• "Something feels off"
• Stiffness in the morning
• Pain in one specific phase of the stroke

Ignore those early signals and it can progress into a persistent tendinopathy. Swimmers with a history of shoulder pain are reported to be up to 11 times more likely to experience it again, which is exactly why the first episode is the one worth taking seriously.

The earlier it is addressed, the easier it is to fix. You don't need to wait until pain stops training.

What actually causes it: evidence versus expertise

When 27 swimming experts — elite swimmers, coaches, high-performance staff and researchers — were asked what causes shoulder injury in swimming, they generated 61 proposed risk factors. Only a handful are supported by the literature, and many have never been formally investigated at all.

When current evidence is compared against expert opinion, three factors stand out as important, modifiable and evidenced:

1. Inconsistent training load
2. "Poor" stroke technique
3. Low posterior shoulder strength-endurance

Load spikes matter more than load volume

It isn't high training load on its own that drives injury — it's sudden change in load. The highest-risk moments in a season are predictable:

• Coming back from a break or illness
• The first squad session after a layoff
• Stepping into a heavier training block
• A change of squad, coach or programme

Where in the stroke the risk sits

Around 70% of pain reports in swimmers localise to the first half of the pull phase. Each phase loads the shoulder differently:

• Entry — near-maximal elevation with slight internal rotation. A hand crossing over the midline increases anterior shoulder stress.
• Catch — a dropped elbow sends force downward instead of backward: less propulsion, more cuff tendon compression.
• Pull — heavy demand on subscapularis, pec major and lat dorsi. With poor posterior cuff control here, the humeral head can translate forward, contributing to anterior pain or clicking.

It's not just about "imbalance"

Elite swimmers typically demonstrate an internal-to-external rotation strength ratio of around 3:2, with similar strength between shoulders despite years of high-volume training. The traditional belief is that swimming creates excessive internal rotation dominance and therefore injury risk — but these ratios are similar to non-swimming populations.

The evidence is less clear-cut than the story suggests:

• ER:IR ratios do not consistently predict shoulder pain
• Swimmers with pain can still show entirely "normal" strength ratios
• However, in younger swimmers not completing dry-land work, heavy training blocks can shift the balance, with internal rotation strength increasing more than external rotation (a 25–28% ratio reduction across a season)

The bigger issue may not be imbalance alone, but whether the shoulder can tolerate the demands being placed on it.

A weak link in the chain

Propulsion runs from trunk to scapula to arm, and a deficit anywhere in that chain shows up as extra shoulder load. Limited thoracic extension or glenohumeral range pushes the shoulder further into elevation and internal rotation. Poor scapulohumeral neuromuscular control leaves the humeral head without a stable base in high-elevation phases. Trunk and lower-limb deficits mean less force transfer, and the arm makes up the difference.

How we assess it

A shoulder assessment for a swimmer isn't a handful of special tests and a shrug. For every swimmer, we ask three questions:

1. Can they achieve the position?
2. Can they produce force in it?
3. Can they produce it repeatedly, as fatigue builds?

Most swimmers pass the first two in the clinic. The stroke tends to fall apart on the third — which is exactly when injuries happen, late in a session.

We start with where the pain sits in the stroke, because it tells us where to look. Entry and catch pain points toward scapulohumeral and neuromuscular control deficits; pull-phase pain toward subscapularis and anterior cuff overload; recovery-phase pain toward the posterior cuff and scapular stabilisers. That is paired with a proper history: recent load changes, stroke mix, coaching or squad changes, training history and previous injuries.

Position is assessed through a qualitative movement screen — overhead range, glenohumeral rotation, neuromuscular control, thoracic extension and rotation, and any signs of hypermobility or instability.

Force is measured objectively. The Athletic Shoulder (ASH) test has been validated in swimmers with excellent reliability, and hand-held dynamometry is the clinical gold standard in this cohort for assessing shoulder rotation strength and ER:IR ratios, specifically using a "break" test.

Repeatability is where most swimmers are exposed. The Posterior Shoulder Endurance Test is a valid and reliable measure, and where useful we will analyse stroke mechanics at the beginning versus the end of a session.

We also test beyond the shoulder, because some tests exist purely to expose what the shoulder is handing off to other joints — a countermovement jump for lower-limb capacity and force transfer, a Pallof isometric for trunk capacity, and kinetic chain integration work such as pikes or crawls.

How we treat it

First, the decision that shapes everything

Is this an under-recovered shoulder or an under-prepared one?

• Under-recovered — the tissue is being reloaded before it settles and adapts. Adding additional heavy loading won't fix it.
• Under-prepared — the shoulder can't tolerate what the swimming programme asks of it. Rest alone won't fix it.

These are two different problems that need different approaches, and everything else comes after this.

Stay in the water

Fully removing a swimmer from the pool should be a last resort. Far more often we modify:

• Volume, intensity and session density
• Stroke mix and drill selection
• Recovery windows around high-intensity sessions

The aim is to build tolerance, not to unload to the point of deconditioning.

Address the deficits you found

The assessment shapes the programme. Rehabilitation should be built on four pillars: neuromuscular control, proprioception, kinetic chain integration and strength endurance.

Bias dry-land work toward external rotation

The repetitive nature of swimming creates a strong internal rotation loading bias. In younger swimmers not completing dry-land work, some studies have demonstrated a shift in rotational strength ratios over a season.

A 2:1 ER:IR emphasis is typical within dry-land strength and conditioning, and there is no clear evidence supporting an ideal ratio. That said, ratios of up to 3:1 to 5:1 have been shown to be well tolerated in this cohort and fit comfortably inside a standard gym programme — often best placed as a warm-up or as a superset alongside a main or accessory lift.

Maintenance and performance

Developing a swimmer's strength and power ultimately serves two aims: overcoming drag forces and increasing propulsive force.

The key for any rehabilitation programme is to ultimately introduce an evidenced, progressive, performance-based dry-land programme. That is built on the "big three" — bench press, chin-up and back squat, or similar variations — eventually progressing toward power-based variations.

When to get your shoulder looked at

You don't need severe pain to justify an assessment. If the shoulder feels "not quite right", is stiffer than usual, or something feels off in one phase of the stroke while you're still completing full sessions, that is the window.

At Step Ahead Sports Physio in Neutral Bay, a full shoulder profile includes mobility testing, ASH force testing, endurance testing and kinetic chain assessment — giving you objective numbers to guide training and monitor progress, rather than a generic protocol.

Book an assessment: Suite 4, 196 Military Rd, Neutral Bay NSW 2089 · 0429 178 916 · stepaheadphysio.com.au

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References

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10. McKenzie A, et al. Identifying evidence–practice gaps for shoulder injury risk factors in competitive swimmers: uniting literature and expert opinion. British Journal of Sports Medicine, 2024.
11. Boettcher C, et al. Is the normal shoulder rotation strength ratio altered in elite swimmers? 2020.
12. Holt KL, Raper DP, Boettcher CE, Waddington GS, Drew MK. Hand-held dynamometry strength measures for internal and external rotation demonstrate superior reliability, lower minimal detectable change and higher correlation to isokinetic dynamometry than externally-fixed dynamometry of the shoulder. Physical Therapy in Sport, 2016;21:75–81.
13. Evans K, et al. Reproducibility and discriminant validity of the Posterior Shoulder Endurance Test. Physical Therapy in Sport, 2020.
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Written by Mitch Lockley, APA Titled Sports & Exercise Physiotherapist and Director of Step Ahead Sports Physio, Neutral Bay.