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Swimming looks like the safest sport there is. No contact, no hard surfaces, no falling. Just water.
So why do so many competitive swimmers end up in physiotherapy?
The answer is volume. A competitive swimmer can complete 60,000 to 80,000 shoulder rotations per week during training. That is not a typo. Every stroke, every length, every session adds to a cumulative load that the body has to absorb, adapt to, and eventually manage.
When the load outpaces recovery, injury follows. And in swimming, two injuries come up again and again: swimmer’s shoulder and swimmer’s knee (also called breaststroker’s knee).
This article explains both, in plain language, so you can recognise what is happening and understand what actually fixes it.
Table of Contents
Part 1: Swimmer’s Shoulder
How common is it?
Very common. Shoulder pain is the most frequent orthopaedic injury in swimmers, with a reported prevalence between 40% and 91% in elite swimmers. That range is wide because definitions differ, but even the lower estimate means nearly half of competitive swimmers will deal with shoulder pain at some point.
This is not a niche problem. It is one of the most common overuse injuries in all of sport.
What exactly is a swimmer’s shoulder?
The term covers several related conditions. The common thread is this: the shoulder was not built to perform thousands of repetitions of full overhead rotation every week. When it does, the soft tissue structures inside the joint, the rotator cuff tendons, the bursa, the bicep tendon, and in some cases the labrum, start to break down faster than they can repair.
Swimmer’s shoulder typically presents as subacromial impingement involving the rotator cuff tendon, bicipital tendon, or subacromial bursa. In plain terms: the structures inside the shoulder are getting pinched or compressed with each stroke cycle.
But here is what most people do not realise. In swimmers, this compression is usually not caused by a structural problem in the shoulder itself. It is caused by muscle imbalance and joint instability.
The muscle imbalance problem
Swimming, particularly freestyle and butterfly, is heavily front-of-body dominant. The chest muscles (pectorals) and the internal rotators of the shoulder get trained hard, while the external rotators, the lower trapezius, and the muscles that stabilise the shoulder blade (scapula) often fall behind.
The cause of shoulder pain in swimmers is multifactorial: overuse, muscle fatigue, laxity and instability, and biomechanics of the swimming stroke. When the muscles that control the shoulder blade weaken, the blade tips forward and outward. This changes the geometry of the shoulder joint at the top of the stroke, creating impingement where there should be clearance.
This is why simply resting swimmer’s shoulder and then returning to the same training load rarely works. The muscle imbalance that caused the problem is still there.
The laxity problem
Competitive swimmers also develop something called acquired laxity, meaning the shoulder joint becomes looser than normal over years of training. Generalised laxity can be present in up to 62% of swimmers. This might sound like a good thing (more flexibility), but it is not. A loose shoulder joint places higher demand on the rotator cuff muscles to actively stabilise the joint during each stroke. When those muscles fatigue, the joint drifts, and impingement occurs.
What swimmer’s shoulder feels like?
The pain usually builds gradually. You notice it first as a dull ache after a long session. Then it starts during training, towards the end of a set. Eventually it can interfere with the overhead recovery phase of the stroke and even with daily activities like reaching for something overhead.
The catch phase of freestyle (when the hand enters the water and begins to pull) and the recovery phase (when the arm comes out of the water and moves forward overhead) are the most common points where swimmers feel the discomfort.
What actually fixes it?
Treatment is generally conservative and should include:
Strengthening of the external rotators and scapular stabilisers. These are the muscles that are chronically underworked in most swimmers. Exercises like prone Y, T, and W positions, cable external rotation, and serratus anterior work are common components.
Stretching the posterior capsule. The back of the shoulder joint in swimmers often becomes excessively tight, which pushes the humeral head forward and increases impingement.
Stroke correction. If the hand enters the water across the midline (a common fault in freestyle called crossover entry), it increases impingement with every single stroke. This is a biomechanical issue that no amount of strengthening alone will fix.
Training load modification. Reducing training volume temporarily while the shoulder heals is necessary, but total rest is rarely the answer. The shoulder needs controlled load to heal and rebuild, not complete offloading.
The important point about surgery: arthroscopic debridement in swimmers has a low success rate with regard to return to sport. Surgery should be a last resort, not an early option, because the root cause is usually muscle imbalance and technique, not a structural problem that a surgeon can fix.
Part 2: Swimmer’s Knee (Breaststroker’s Knee)
This one is specific to breaststroke. If you swim freestyle, backstroke, or butterfly and have knee pain, a different assessment is needed.
How common is it?
Knee pain figures range from 34% to 86% for a single knee episode in swimmers, being highest in breaststrokers. In competitive breaststroke swimmers, this is one of the most expected overuse injuries.
Why breaststroke is hard on the knee?
The breaststroke kick is unique in swimming. Unlike the flutter kick in freestyle, which is a relatively simple up-down motion, the breaststroke kick involves the knee being driven outward (abducted), then snapping inward (adducted) against the water resistance. The technical term is a whip kick.
This creates a high valgus load on the knee: a force that pushes the shin outward relative to the thigh, placing stress on the medial (inner) side of the knee. Repeat this hundreds of times per session, several sessions per week, and the medial collateral ligament (MCL), the adductor tendons, and the medial plica (a fold of joint lining) all come under sustained strain.
What swimmer’s knee feels like?
The pain is on the inner side of the knee. It comes on during the kick phase of breaststroke, and in more advanced cases, it persists after training and the next morning.
Most swimmers notice it is not there during freestyle. The moment they switch to breaststroke sets, the pain comes back. That is a reliable indicator.
What makes it worse?
Researchers have found that breaststroke swimmers with knee pain are more likely to have limited hip internal rotation. When the hip cannot internally rotate freely, the knee compensates by taking on more of the rotational stress. This is a kinetic chain issue (the same concept as in foot or ankle problems causing knee and hip pain elsewhere): the problem is showing up in the knee, but the root cause is often in the hip.
Poor technique, specifically excessive external rotation of the foot during the kick, amplifies the valgus stress further.
High training volume of breaststroke sets, without adequate buildup, is the most consistent risk factor across all research.
What actually fixes it?
Stroke technique correction is the most important intervention. A coach or physiotherapist who can observe the kick in the water and identify excessive external rotation or valgus at the knee can make a significant difference.
Hip mobility work, especially hip internal rotation flexibility, reduces the compensatory load through the knee.
Strengthening the adductor and hip muscles helps control the outward flare of the knee during the kick phase.
Temporary reduction in breaststroke volume, particularly the 200m and 400m events, which research shows carry the highest risk for knee overuse injuries.
Proprioception and knee stability exercises done out of the water support the joint during the loaded phases of the kick.
Most swimmers with this condition recover fully with appropriate management. The cases that drag on are usually those where the swimmer kept training through it for months without addressing the technique or the hip mobility issue.
A self-check swimmers can do
For shoulder: Lie face down on a bench or bed with your arm hanging off the edge. Slowly raise your arm sideways and hold for 10 seconds. If you feel significant weakness or pain compared to the other side, your external rotators and lower trapezius are likely understrength. This is not a diagnosis, but it tells you something.
For knee: Stand up and slowly perform a breaststroke kick motion in the air, without the water. Notice whether your knee drifts outward (valgus) during the outward phase. If it does, that is the movement pattern that is loading your medial knee in the pool.
For coaches
A swimmer’s shoulder is usually a training error before it is an injury. A sharp increase in yardage, adding extra sessions, or changing stroke mechanics without adequate adaptation time are the most common triggers. Training volume is the single most modifiable risk factor.
Introduce overhead dry-land strengthening as a year-round component of your programme, not just in pre-season. Many shoulder injuries could be prevented with two to three sets of scapular stabilisation and external rotation work per training week.
For breaststroke knee: film your swimmers’ kick from the side and from below if you have an underwater camera. Visible external rotation of the foot and outward flare of the knee are correctable technique faults that are much easier to fix early.
For parents
Young competitive swimmers are particularly vulnerable to overuse injuries because their training volumes often increase faster than their bodies can adapt.
If your child complains of shoulder pain that is on one specific side and gets worse during training rather than just after, that is worth acting on. Do not wait for it to become constant pain.
Knee pain in a breaststroker that persists beyond one or two weeks, or that comes back every time breaststroke sets increase, needs a physiotherapy assessment. It will not resolve on its own if the underlying technique and hip mobility issues are still present.
The bottom line
Swimming injuries are overuse injuries. They build quietly and then tip over into pain. The shoulder and the knee are the two joints that pay the price most often.
Both conditions respond very well to conservative management: technique correction, strength work, and sensible load management. Both respond poorly to total rest followed by returning to the same training without anything changing.
If you are a swimmer dealing with shoulder or knee pain, the question is not just “what is hurting?” It is “why is it hurting?” The answer almost always involves something about how you move, how much you train, or both.
That is what a good sports rehabilitation assessment looks for. Not just the symptom. The reason behind it.
Are you a swimmer dealing with shoulder or knee pain?
At Activ Insight, our sports rehabilitation team works with swimmers across India. We use movement analysis to identify the specific muscle imbalances and technique faults that drive swimming injuries, and build a return-to-training plan around you.
