Swimmer's Shoulder in Triathletes: Load, Not Just Technique

For many age-group triathletes, swim progress follows the same pattern. Commit to more swimming, add a few hard sets, maybe pick up some paddles, and a few weeks later one shoulder starts to ache. It's often put down to technique, and sometimes that's part of it. But the research on swimmers points more consistently to something else: how much and how quickly you've been loading the shoulder.

This article covers what the evidence says about swimmer's shoulder, what's different about triathletes, how to build swim load more safely, and when to stop and get help. It doesn't diagnose or treat anything. Persistent or worsening shoulder pain needs a proper assessment.

What "swimmer's shoulder" usually is

"Swimmer's shoulder" is a loose term for pain around the front and top of the shoulder in swimmers. A key study helped pin down what usually lies behind it.

Sein and colleagues (2010) studied 80 elite swimmers aged 13 to 25, using questionnaires, clinical examination and shoulder laxity testing, with MRI in 52 of them. Their findings:

• 91% reported shoulder pain.
• 84% had positive impingement signs on clinical testing.
• 69% of those imaged had supraspinatus tendinopathy, an irritated and thickened rotator cuff tendon.
• Hours of swimming per week and weekly distance both correlated significantly with tendinopathy.
• Shoulder laxity (looseness) showed minimal association.

The authors concluded that supraspinatus tendinopathy is "the major cause of shoulder pain in elite swimmers" and that it is "induced by large amounts of swimming training." They challenged the older idea that loose shoulders were the main problem.

These were elite, mostly young swimmers doing far more swimming than any age-group triathlete. But the mechanism is a familiar one. A tendon is loaded repeatedly, and when load outpaces its ability to adapt, it becomes irritated and painful. TriForward's article on calf and Achilles capacity describes the same principle for the lower leg.

Volume across the lifespan

A 2020 systematic review by Feijen and colleagues in the Journal of Athletic Training pulled together 12 studies with 1,460 competitive swimmers across age groups. That included a masters category spanning ages 23 to 77, which makes it more relevant to age-groupers than most swim research.

Key findings:

• Adolescents had the highest rates of shoulder pain (91.3% in the studies reviewed).
• Weekly swim volume and years of competitive swimming were significantly related to supraspinatus tendon thickness, and all swimmers with tendon thickening had shoulder pain.
• Swimmers with and without shoulder pain differed in training exposure in both the adolescent and masters groups.
• The firmest conclusion, rated "level II" evidence, was that swim volume was associated with shoulder pain in adolescents.

The authors recommended monitoring both acute and chronic training volume across the year and cautioned specifically against sudden increases in swimming volume. They also noted that the research can't yet define a pain-free volume threshold.

The evidence is strongest for adolescents. For masters swimmers it suggests a similar relationship, from fewer studies. That's still the best guide available for adult triathletes.

What's different about triathletes

Only one study we found looked directly at shoulder injury risk factors in amateur triathletes. Schorn and colleagues (2018) carried out a retrospective analysis of 193 amateur triathletes:

• About 6% had sustained an acute shoulder injury, and 36 athletes reported an overuse injury.
• Overuse injuries occurred at about 0.33 per 1,000 training hours.
• Paddle use was associated with overuse injuries.
• Age, body mass index and triathlon experience weren't significant predictors.

To put that rate in context, here's TriForward's own arithmetic, not a figure the study reported. An athlete training about 6 hours a week across all three sports logs roughly 300 hours a year. At 0.33 overuse injuries per 1,000 hours, that works out to about one shoulder overuse injury for every ten athletes per year. That's not rare, and it's a rough average that will be higher for athletes with risk factors like heavy paddle use.

Retrospective studies depend on athletes remembering injuries and training habits accurately, and an association isn't proof that paddles cause injury. Athletes might use paddles more when they're already swimming more, for example. But it fits with the general picture of shoulder injury as a load problem, since paddles increase the force on the shoulder with every stroke.

Beyond that study, several features of triathlon training plausibly increase shoulder load. These are TriForward's inferences, not tested risk factors:

• Seasonal ramps. Many triathletes swim little in the off-season, then increase sharply in spring. That's the "sudden increase" the Feijen review warned about.
• Stacking. A new swim block, the start of open-water season, more paddle work and heavier upper-body gym sessions often all happen in the same few weeks.
• Wetsuits. A tight or poorly fitted wetsuit can restrict shoulder movement, possibly changing stroke mechanics over long swims.
• Sighting. Repeatedly lifting the head in open water changes body position and may alter shoulder loading.
• Inefficient technique. Triathletes tend to lose more stroke power to the water, as Toussaint's 1990 comparison showed. Plausibly, that means more strokes and more effort per length for the same distance.

The role of technique

Technique is often blamed first, and it can contribute, but the evidence is more about load. Coaches commonly point to a few patterns that may increase shoulder stress. These are coaching observations rather than proven causes:

• Hand entry crossing the midline, which may push the shoulder into a more provocative position.
• Very flat body position with little rotation, which may force more of the recovery through the shoulder.
• A thumb-first, strongly internally rotated hand entry.
• Breathing only to one side for long periods, concentrating rotation demands on one side.

If video or a coach identifies one of these, it's reasonable to address it, gradually, as discussed in "Filming Your Stroke." But changing technique is itself a change in load. Make one change at a time, and back off if the shoulder becomes more painful.

Does shoulder strength work prevent injury?

Rotator cuff and shoulder-blade exercises with bands are near-universal in swimming. The rationale is that swimming strengthens the muscles that rotate the arm inwards more than those that rotate it outwards, creating an imbalance.

The direct evidence is limited. In a 2023 randomised trial by Della Tommasina and colleagues, 22 male swimmers added an 8-week elastic-band programme for the shoulder rotators, or continued aquatic training only. The band group showed improvements in external rotation strength and rotator balance, but these weren't statistically significant. The study was small, short and didn't measure injury rates, so it can't show whether such programmes prevent injury.

The practical position: band and shoulder-blade work is cheap, low-risk and plausibly helpful, and there's good reason to keep doing it. But it isn't a substitute for managing swim load. TriForward's article "Dryland Strength That Transfers to the Water" covers how to include it alongside other strength work.

Building swim load more safely

There's no validated swim-volume formula for triathletes. The following is TriForward's practical guidance, based on the volume findings above and general load-management principles.

Increase gradually

Raise weekly swim volume in small steps, and hold it steady for a while before increasing again. The research can't give a safe percentage. TriForward's run article "Forget the 10% Weekly Rule" explains why fixed percentage rules are a poor fit for individuals anyway. The principle that matters is to avoid big jumps, especially after a break.

Don't stack changes

Change one major variable at a time: volume, intensity, paddle use, open-water swimming or heavy upper-body gym work. If you're starting a new swim block, it isn't the week to also start heavy pull-ups and paddle sets.

Treat paddles as a strong stimulus

Introduce them in small doses, use smaller paddles, avoid long continuous paddle swims early on, and stop using them at the first sign of shoulder pain. The association with overuse injury in amateur triathletes is reason enough for caution.

Plan the seasonal ramp

If your swimming drops off over winter, rebuild over several weeks before the season rather than jumping straight to full volume in spring. Keeping one or two maintenance swims a week through the off-season, even if short, may make the spring rebuild smaller. That's an inference from the "avoid sudden increases" advice.

Vary the stimulus

Bilateral breathing at least some of the time, mixing in some backstroke if your shoulders tolerate it, and varying set types may spread load across tissues. This is coaching logic rather than tested prevention.

If your shoulder starts to hurt

Early action usually shortens the problem. A sensible approach:

1. Reduce, don't necessarily stop. Cut volume and intensity, and remove paddles. Many people can keep swimming at a lower load without making things worse.
2. Avoid provocative positions and sets. If certain strokes, breathing sides or efforts reliably cause sharp pain, take them out for now.
3. Keep moving and keep training elsewhere. Bike and run training can continue, and pain-free shoulder strengthening is often part of rehabilitation, ideally guided by a physiotherapist.
4. Get assessed if pain persists for more than a week or two, is getting worse, or disturbs sleep. A physiotherapist or sports physician can identify what's involved and set a structured return.
5. Return gradually. Rebuild swim load in steps once pain allows, rather than going straight back to where you were.

Seek prompt medical assessment for night pain, significant weakness, numbness or tingling in the arm, a feeling the shoulder is unstable or "slipping," or pain after a fall or impact. These can indicate problems other than overuse tendinopathy.

Monitoring your swim load

The Feijen review recommended tracking both short-term ("acute") and longer-term ("chronic") swim volume across the year. You don't need special software. A simple log is enough:

• Weekly swim distance or time. Note how this week compares with your average over the past three to four weeks. A week well above your recent average is the kind of spike to be wary of.
• How much was hard. Threshold and speed sets load the shoulder more per metre than easy swimming. A rough session rating (easy, moderate, hard) is enough.
• Paddle metres. Track them separately, given the association with overuse injury.
• Shoulder symptoms. A quick 0-10 rating after each swim. A rising trend over a week or two is an early warning worth acting on before it becomes an injury.

None of these measures has been validated as an injury predictor in triathletes. Their value is in making big jumps and creeping symptoms visible, so you can adjust early.

A worked example: the spring ramp

This is an illustration of the principles above, not a tested protocol. Imagine an athlete who swam once a week, about 1,500 m, through winter, and wants to reach three swims and roughly 7,000-8,000 m a week by early summer.

• Weeks 1-2: add a second swim. Total about 3,000-3,500 m. Mostly easy and technique work, no paddles.
• Weeks 3-4: hold two swims, extend them slightly. Total about 4,000-4,500 m. Introduce one short threshold set.
• Weeks 5-6: add a third, shorter swim. Total about 5,000-5,500 m.
• Week 7: hold, or reduce slightly, to consolidate.
• Weeks 8-10: build towards target volume. Introduce small paddles in short doses (a few hundred metres a week) only if the shoulder is symptom-free.
• Open-water sessions: start them partway through, counting them as part of the total rather than extra on top.

The key features are a gradual rise, periodic steady weeks, intensity and paddles added later rather than at the start, and no new heavy upper-body gym work layered on during the steepest part of the ramp. If shoulder symptoms appear at any stage, drop back to the previous week's load until they settle.

Masters swimmers and slower adaptation

The Feijen review included masters swimmers aged 23 to 77 and found training exposure differed between those with and without shoulder pain in that group, as it did in adolescents. There's no research we found defining how much more gradually older triathletes should build swim load. But tendons generally adapt slowly, and many masters athletes report needing longer to recover from big training increases. A cautious, reasonable inference is that older athletes should build more gradually, include more steady weeks, and react earlier to symptoms than younger athletes might.

References

• Sein ML, Walton J, Linklater J, Appleyard R, Kirkbride B, Kuah D, Murrell GAC. Shoulder pain in elite swimmers: primarily due to swim-volume-induced supraspinatus tendinopathy. British Journal of Sports Medicine, 2010. doi:10.1136/bjsm.2008.047282
• Feijen S, Tate A, Kuppens K, Claes A, Struyf F. Swim-training volume and shoulder pain across the life span of the competitive swimmer: a systematic review. Journal of Athletic Training, 2020;55(1):32–41. doi:10.4085/1062-6050-439-18
• Schorn D, Vogler T, Gosheger G, Schneider K, Klingebiel S, Rickert C, Andreou D, Liem D. Risk factors for acute injuries and overuse syndromes of the shoulder in amateur triathletes: a retrospective analysis. PLoS ONE, 2018;13(6):e0198168. doi:10.1371/journal.pone.0198168
• Della Tommasina I, Trinidad-Morales A, Martínez-Lozano P, González-de-la-Flor Á, Del-Blanco-Muñiz JÁ. Effects of a dry-land strengthening exercise program with elastic bands following the Kabat D2 diagonal flexion pattern for the prevention of shoulder injuries in swimmers. Frontiers in Physiology, 2023. doi:10.3389/fphys.2023.1275285
• Toussaint HM. Differences in propelling efficiency between competitive and triathlon swimmers. Medicine & Science in Sports & Exercise, 1990;22(3):409–415. PubMed 2381311