The Lane and the Numbers That Hide: Notes of a Swimming Analyst

On the night of the women's 800-metre freestyle final, I sat in front of the screen with a sheet of paper divided into eight empty boxes. Each box was one 100-metre segment. The television clock ticked through hundredths of a second while my hand hurried to record each number. When the woman leading at the halfway mark touched the wall in fourth place, I was not surprised. The eight boxes had predicted it from the fifth segment, when she swam faster than she had in the opening leg. A body going faster in the middle of an 800-metre race is not full of energy. It is spending its last reserve. The winner was the steadiest swimmer, not the fastest at any point. Over years of following swimming, I have learned that the order of finish is only a full stop. The real story lies in the numbers the cameras never hold on long enough: stroke rate, distance per stroke, reaction time off the blocks, and the thing few notice — the underwater distance after every turn. Numbers do not lie, but they know how to hide things. In a swimming pool, what is hidden best is the time spent outside the television frame. I began my career at a sports newsroom as a reporter covering swimming. Back then I believed that the feeling of those inside the sport was the most accurate measure. A coach told me his athlete was in great form, and I wrote it down word for word. A swimmer said she had just had the best training session of her life, and I put it in print. The following season, the praised swimmer went nearly two seconds slower than her own record. No one lied. Feeling and the stopwatch simply live in two different worlds. Since then I changed how I work. For every swimming piece, I build a spreadsheet first. A column for time, a column for stroke rate, a column for efficiency per stroke. The pool became a laboratory, and I became its record keeper. My spreadsheet has no room for luck. The pool learns to count Swimming has changed faster than almost any other sport in the past two decades, and most of that change comes from how people measure it. Fans used to know only the final result. Now, every time a hand touches the wall, dozens of data points appear at once on screen: reaction time, the first 50-metre split, strokes per minute, strokes per length, and time spent underwater. Electronic timing with touchpads at the wall long ago replaced the hand-held stopwatch, but the real revolution came with underwater cameras. Officials can now count precisely how far a swimmer travels before surfacing. This is the most important number television rarely shows. International rules allow a swimmer to stay underwater for a maximum of 15 metres after the start and after each turn. Never more than 15 metres. In a 50-metre lane, almost a third of the distance can happen entirely underwater, and a strong swimmer's underwater speed is higher than their surface speed. The data shows that most of the gap between elite swimmers and the rest is not in the arm stroke. It lies in the underwater phase, in the turn, and in the moment of surfacing at exactly the right time. To me, PPDA is not a number, it is a confession. In swimming, the equivalent confession signal is the length of the underwater phase — it tells me how far a swimmer has prepared body and technique. I have stayed up late after many finals, going back through slow-motion footage to count strokes by hand. The work is not glamorous. But it is what lets me see what a medal table never says. The anatomy of a lane A lane can be divided into four phases. The start, the underwater glide, the surface swim, and the touch. Each phase has its own unit of measurement. Reaction time off the blocks usually sits between 0.6 and 0.7 seconds for elite swimmers. A 0.1-second difference seems small, but in a 50-metre event it can be the gap between gold and fourth place. The underwater phase is where I focus most. After the start, a swimmer performs a forward dive and holds the body taut like an arrow. In freestyle and butterfly, they keep the body underwater with a dolphin kick. Each kick produces propulsion but consumes oxygen. Surfacing too early loses speed; surfacing too late drains energy for the rest of the race. The best swimmers master this moment to the tenth of a second. The surface swim is where arm technique and breathing rhythm decide. Too fast a stroke rate reduces propulsion because each stroke shortens. Too slow a rate loses momentum between strokes. The optimal zone for each swimmer is a balance point that only data can reveal. Distance per stroke multiplied by stroke rate gives average speed. To go faster, you must raise one variable without letting the other collapse. The touch — the finish — is also a technique. It is the moment a swimmer extends toward the wall instead of taking one more full stroke. In short-distance events, perfect timing on the finish decides entire medals. I once watched a final in which two swimmers touched within hundredths of a second of a record. The difference was not strength. It was who calculated the remaining strokes well enough to extend at the right moment. Fifteen metres underwater I have a personal rule: never conclude anything about a swimmer before watching their underwater phase at least three times. This is where uncomfortable truths tend to appear. A swimmer can have a beautiful arm stroke, a powerful body, and lightning reflexes, yet surface after only 8 metres underwater. That number, 8 metres, explains almost the entire gap between them and the leader. Since the 15-metre rule was enforced strictly, underwater training has become mandatory in the programmes of every strong team. Yet there is a physiological limit. The body consumes oxygen underwater while unable to breathe freely. The longer the glide, the more the reserve is drained, and it will be paid for later in the race. This is an optimisation problem, not a fixed indicator. What fascinates me is how different coaching schools treat the 15 metres. Training centres in North America and Oceania tend to exploit this distance to the maximum, pushing swimmers to the legal ceiling. Some Asian swimming cultures prefer an even rhythm and an earlier surfacing to keep breathing steady. No school is absolutely right. It depends on body structure, endurance, and the style of each swimmer. When analysing any performance, I always cross-check two sets of data. One is the underwater set — glide length, number of kicks. The other is the surface set — stroke rate, stroke count. Only when these two agree do I allow myself a judgement. Otherwise, any conclusion is just a feeling dressed in numbers. The rhythm of the 800 metres In long-distance events, split times reveal what spectators cannot see. People usually cheer for the leader, but in distance swimming, leading after the first 200 metres is a dangerous position. Water pressure and psychological pressure combine to make a swimmer burn energy faster than needed to hold that position. An ideal distance performance follows an even-pacing strategy, in which each 100-metre segment is nearly identical, or even slightly faster at the end. This is called a negative split, when the later segments are faster than the earlier ones. It saves reserve energy for the decisive moment. The opposite style — going out fast and fading — is the classic trap. Data shows that swimmers who fall into it usually collapse from the 600-metre mark onward. That is exactly what I read in my eight boxes that night. Emotion is the most expensive thing in the transfer market, and in swimming, the thrill of a lightning start is an overpriced commodity. An impressive start earns applause, but applause does not keep a swimmer afloat in the final metres. When records are inflated One cannot discuss modern swimming without the period from 2026 to 2026. That was when high-tech swimsuits, often called shark-skin suits, made world records fall again and again. Within a few months, dozens of records were broken, many lasting only days. What matters is that those records did not reflect pure human ability. They reflected a combination of human and technology. When the international federation banned high-tech suits, many records froze for years. Only later did some of those era records fall to swimmers in ordinary textile suits. My lesson from that period is clear. A number only means something when placed in the context that produced it. Comparing the times of two swimmers from different eras without adjusting for technology is an analytical error. To be fair, an era-adjustment factor must be applied. That was also when I recognised the value of historical precedent. When a young swimmer breaks a record, the first thing I do is not to cheer. I open the spreadsheet, compare it with the record curve over twenty years, and ask whether this is a genuine human advance or simply the result of a change in competition conditions. A map of power and the flow of talent The map of world swimming power is not static. Traditional powers still hold many strengths in speed and endurance events, but the flow of talent is shifting. Countries that once had no long-distance swimming tradition are beginning to produce finalists. This does not come from magic. It comes from the training system. National training centres invest in facilities, hire foreign coaches, and send young swimmers to train at major centres in Europe and North America. When a young swimmer leaves home to train in a more competitive environment, technical progress often comes with a change in competitive mindset. There is a notable mechanism in the international development system. Big clubs usually do not train swimmers from scratch. They build networks of satellite clubs in places with low training costs or youth-development incentives. Swimmers are raised at the satellite, then brought to the main centre once they are good enough. This approach saves money and pulls more talent into their orbit. For a small swimming nation, this is a double-edged sword. The satellite system gives swimmers a better chance to train, but it also drains the best talent outward. The home country develops the swimmer, but the medal belongs elsewhere. The career curve and the youth trap In swimming, age is a complex variable. Some events peak very early, when the body is still light and flexible. Others rely more on experience, accumulated endurance, and an understanding of race rhythm, allowing swimmers to shine later. There is a trap I have seen many times. A young swimmer produces an impressive result at fifteen or sixteen, and the media calls them a prodigy. Then the body changes with maturity. Height rises, fat ratios shift, muscle structure changes. These changes break the technique that had been trained to fluency. The swimmer must rebuild their stroke from scratch, and many never get through that phase. The question I always ask before writing about a prodigy is this: is this a lasting advance, or a temporary spike. The way to tell lies in the improvement curve. If times keep falling steadily across multiple seasons, that is a real signal. If a result drops once and then stalls, it may be only a moment. On the team side, the quality of the support system is decisive. Whether a swimmer has the right coach, a sports-science team, and a rehab department determines how long a career lasts. Shoulder and back are the most common injury zones for freestyle and butterfly swimmers. The knee is the weak point of breaststrokers. Pool injuries are usually quiet, but they accumulate and silently erode performance. Vietnam and the pool equation Vietnamese swimming holds an interesting place on the regional map. We have had swimmers who made an impact at regional events and even at major games. But seen through the eyes of data, the gap between Vietnam and the world's leading group remains large, and it is not only a gap in results. It is a gap in systems. A strong swimming nation needs standard pools across many provinces, a talent-identification system from a young age, properly trained coaches, and a dense enough domestic calendar for regular competition. Miss any link, and talent withers before it reaches the international threshold. There is a paradox I always ponder. When a Vietnamese swimmer performs well, the press and fans focus on that individual. But behind one talent lies a whole chain of conditions: family investment, local support, dedicated coaches. When that swimmer retires, if the system has not produced the next one, the gap shows immediately. Vietnam's swimming problem is therefore not finding a new prodigy. It is building a continuous talent pipeline. A healthy swimming nation is not measured by one individual's medals, but by the depth of the reserve squad behind them. On the edge of the rules and the question of fairness Swimming is one of the sports with the most detailed and strict rulebooks. From the start, to the underwater phase, to the turn for each stroke, to the touch. Every detail is specified, and officials can disqualify a swimmer for a small technical fault. In breaststroke, the rules are especially strict. A swimmer may perform only a single dolphin kick after the start and after each turn. The arm movement must also follow a set sequence. A small deviation can lead to disqualification. I have seen cases where a swimmer finished first but was disqualified after officials reviewed the footage. Behind the technical rulebook is a broader governance system, including anti-doping regulations. Swimming has been through many doping-related cases, and each one has left aftershocks among fans. For a data analyst like me, the most important lesson is to distinguish clearly among three kinds of information: confirmed violations, procedural disputes, and media allegations. These three cannot be treated the same way. A case with an official conclusion can be analysed directly. A procedural dispute must wait for the investigation, with no speculation. An unverified allegation must never be steered by the crowd. A writer's credibility is built over years and can collapse from a single repetition of an unverified rumour. The trap of the number Here I must warn myself. Readers may think I worship data. That is wrong. Data is testimony, and all testimony can be wrong, incomplete, or misread. There are three traps I always try to avoid. The first is forcing a single indicator into a grand conclusion. A swimmer with a fast stroke rate is not necessarily the most efficient, because a fast rate with a shortened stroke can signal an inefficient action. To conclude, you must place stroke rate next to distance per stroke and split times. The second is mistaking correlation for causation. A relationship between two numbers does not mean one causes the other. There are coincidences in data that, without care, an analyst easily turns into a rule. Such rules usually collapse the moment they are applied to a real race. The third is forgetting that swimming has factors that cannot be measured. The psychology before a major final, an unexpected change in pool conditions, or simply a day when the body will not cooperate, are not on the spreadsheet. A spreadsheet records what happened, but not what could have happened. The pool taught me something similar to long-distance open-water swimming. You can measure the waves, the wind, the current, but no one swims well only by reading numbers. You have to get into the water. So every time the data says something too attractive, I pause and ask whether this indicator truly represents the conclusion I want. If not, I put the number back where it belongs: a piece of the puzzle, not the whole picture. In that Saigon summer, I learned that data, too, needs watering. A dry spreadsheet will tell no story. To make numbers come alive, they must be placed in a context of people, effort, and disappointment. Signals for the next round Looking ahead, I believe swimming will keep shifting in three directions. Data will become ever more detailed, as sensors and cameras measure the propulsion of each stroke. The gap between large and small swimming nations will not narrow quickly, because investment in development systems takes years to pay off. And distance swimmers will increasingly race with even-pacing strategies, as sports science shows that to be optimal. As for me, I will still be sitting there, in front of the screen, with my sheet of empty boxes. I will still record every number. Because in a 50-metre lane, there are things only numbers can tell, and there are things numbers deliberately hide. Football stops moving, but 2,400 matches still whisper in my spreadsheet. For swimming, I keep my own mantra. Every lane is a data point, but not every data point is a perfect lane. Fans can keep cheering for the leader. The analyst stays behind with eight boxes. Those two worlds are separated by exactly one medal, and sometimes by an entire truth.