The Swimmer's Shoulder: Every Stroke Cycle Withdraws From the Tendon's Account

One March morning, I sat in front of a training-volume board for a group of competitive swimmers. The left column recorded metres per session. The middle column recorded stroke cycles. The right column recorded rest days. A seventeen-year-old swimmer specialising in the 200-metre freestyle had a middle column rising steadily for nine consecutive weeks, while the right column was almost empty. In the tenth week, she missed three sessions with pain in her right shoulder whenever she raised her arm above her head. I went back through my old logs. Numbers stay silent, but their sequence always tells a story. In my records, this swimmer had never fallen, never collided, never been landed on. Her injury came from a movement repeated tens of thousands of times — correct in technique, correct in rhythm, correct in programme design. Precisely because it was correct, it was the hardest thing to see. At Lạch Tray, I learned to read injuries from the first numbers, and that lesson followed me from the pitch to the pool. A footballer breaks down in a tackle and everyone remembers. A swimmer's shoulder fails after hundreds of thousands of stroke cycles and nobody remembers — not even the swimmer. That is why I started building my own monitoring board for swimming. Swimming sits in the low-contact group of sports. There is no tackle, no single-leg landing, no two heads colliding. As a result, the default assumption outside the sport is that swimming is joint-safe, that swimming is rehabilitation, that swimming is the sport of longevity. That assumption holds for recreational swimmers and fails for anyone training at elite volume. In sports-medicine records, the shoulder is the number-one injury site for competitive swimmers, typically accounting for roughly forty to sixty per cent of all cases in the racing group. Next come the lower back, the knee — especially among breaststrokers — and the neck. Freestyle is the most common stroke and also contributes the most shoulder cases, simply because it occupies the largest share of training time. To understand why the shoulder breaks down, you have to look at the pull. As the hand enters the water and begins to press downward, the upper-arm bone rotates inward and elevates to roughly shoulder height. This position narrows the subacromial space — the small gap between the head of the upper-arm bone and the arch of the shoulder blade. The rotator-cuff tendons and the long head of the biceps tendon run through that narrow gap. Every stroke cycle compresses them once. Once is nothing. Ten thousand times a week is a different story. Take a simple calculation I routinely show to coaching staff. A swimmer covering about fifty kilometres a week — the kind of volume found in high-performance squads in many parts of the world — with an average stroke length of two metres, completes roughly twenty-five thousand stroke cycles per week. Multiply by four and the figure passes one hundred thousand per month. For a young swimmer who specialises from the age of twelve, by twenty the number of stroke cycles sits in the millions. No shoulder joint is built for that arithmetic unless a prevention programme travels alongside it. In my most recent monitoring block, twenty-six weeks with thirty-four swimmers, I recorded twelve cases of shoulder pain severe enough to require a reduction in training volume, four of which needed a full week or more off. Eleven of the twelve occurred in the group with the highest weekly metres and the most consistent dryland attendance. The more interesting detail lies elsewhere: six of the twelve began not at peak volume, but in the first and second weeks after a short break. That is the point I want people to hold on to. Every fall has a graph, and every graph has a breaking point. In swimming, the shoulder's breaking point is not at the top of the volume curve. It is on the steep upward slope, when the body has not yet regained its base fitness and the joint's stability. This is the classic blind spot, and it repeats in almost every squad I have monitored. Most swim programmes still allocate the bulk of their time to the water, while dryland work — shoulder strength, scapular stability, postural control — is treated as secondary. There is a reason for the error. It begins with the idea that heavy swimming is already a strength exercise. Physiologically, that is only half true. High volume builds endurance, but muscular endurance is not the same as joint stability. The shoulder blade needs strength to control rotation and elevation, which straight-line swimming does not build enough of. Age deserves a mention too. This is where my data and that of my colleagues converge. Swimmers under fifteen show lower injury rates than the over-seventeen group, but the under-fifteen group shows the fastest growth in cases as volume shifts from recreational to semi-elite. The problem does not sit in age itself. It sits in the speed of volume increase and the shortened recovery window. I remember a conversation with the head coach of a youth squad, a man with years of experience and genuine results. He said something I wrote in my notebook: "The kids don't hurt because they swim a lot. They hurt because they swim a lot every single week." He was close to right about the mechanism and wrong about the conclusion. They hurt because of both, but the part we can actually intervene in is the second — the structure of the week and the rhythm of load increase. The counter-current view here is this: faulty technique is not the main culprit in most shoulder cases in swimming. The familiar explanation — "you pulled wrong, so your shoulder failed" — is easy to accept because it gives us someone to blame and something to fix: the movement. But in the data I monitor, most swimmers with shoulder pain had stable technique and had not changed their stroke pattern in the period before injury. What changed was volume, session count, rest, intensity. The body is a closed system, but data is the key that opens it. Fixing technique is necessary, but fixing technique without reading the volume board only treats the symptom. Another counter-current point, and I know it is not easy to hear in many coaching rooms: shoulder pain in swimming is an accumulative overload injury, and it is very good at disguising itself. Swimmers have no collision that forces them to stop. They have no opponent kicking their leg. So the only signal is sensation, and sensation is filtered through a training culture that prizes silence and endurance. In swimming, complaining is treated as weakness. That is why so many cases reach me late — not because there were no symptoms, but because the symptoms were hidden. I also want to be clear about what I do not support: blaming the coach or the swimmer. In almost every case I handle, nobody intended to harm anyone. There is a chain of small decisions, each reasonable at the moment it was made: add a session because a meet is coming, drop a rest day because it rained, keep the programme unchanged because last week everyone coped. That chain accumulates into the breaking point. This is why I emphasise process over the result of any single session. So what does a workable process look like? The first step is to log three numbers every session: metres swum, estimated stroke cycles, and days since the last rest. The next is to cap the weekly increase in volume at a modest rate, and deliberately deload every two to three weeks. Alongside that, separate the dryland work for scapular stability and external rotation. And the one that cannot be skipped: set a clear alarm threshold for pain, so swimmers know when they are allowed to speak up without being seen as weak. There is a question I am often asked after talks: does cutting volume mean a healthy shoulder? My answer is that it is not that simple. Cutting volume does not create competitive capacity, and nobody wins by swimming less than everyone else. What is needed is not less swimming, but swimming inside a structured rhythm. Rhythm here is not a vague idea. It is a number: the ratio of loading weeks to deload weeks, the length of rest required for tendon recovery, the number of dryland sessions per thousand metres. For the Vietnamese swimming system, this is an interesting transition period. The number of pools is rising, the number of properly coached swimmers is rising, and public interest in national competitions is rising with them. That means the training volume of youth squads will keep climbing. If load monitoring and recovery work do not rise in step, we will see more shoulder cases over the next three to five years, and we will hear the same familiar explanations about "bad technique" or "weak physique". I want to say this early, so that the numbers are recorded before the conclusions are formed, rather than afterwards. In every sport there is a gap between what we see and what is happening. In football, video fills that gap. In swimming, it has to be filled by a logbook. No video shows you a rotator-cuff tendon fatiguing across three weeks. Only a recorded number shows you how week three differed from week one. What I want to leave behind is not a fixed formula but a habit. Write down three numbers each session, and read them back every two weeks. If a swimmer arrives at their first injury, what I want to see is not an explanation but a record sheet. At that point, nobody will ask why — they will know exactly which week it started. A swimmer's shoulder fails after hundreds of thousands of stroke cycles. It does not fail in a single afternoon. And anyone who says otherwise is reading the graph wrong.