On the evening of 12 April, at an indoor pool in Ho Chi Minh City, I sat in the fourth row, laptop open, a stopwatch in my left hand. A fifteen-year-old swimmer dived into lane four for the final of the 200 metre individual medley. I captured eight split marks across four lengths. When the race ended, the organisers sent the results file: two columns. One column for the finishing time, one for the placing. The four lengths disappeared. The reaction time off the blocks disappeared. The turn times disappeared.

I typed those eight marks into a spreadsheet by hand. Eight marks for one swimmer. That session alone contained more than three hundred swims. Roughly ninety-nine percent of the meet's movement data does not exist in any form.

If this were a football match, I would have dozens of variables per team. Here I have exactly one duration: 2 minutes 21.47 seconds. And that alone tells no story at all. It says only that somebody finished. It does not say how they finished, or whether it can be repeated tomorrow.

A sport that generates data and then loses it

Swimming is the most data-rich of the purely measured sports. Every 200 metre swim generates at least eight split marks, four turn times, and eight stroke-rate readings if anyone is counting. A continental championship generates thousands of data points in three days of competition. At events run by World Aquatics, 50 metre splits are published openly for every final, along with reaction times off the blocks.

At home, we have almost nothing.

I have followed Vietnamese swimming since 2026, when I wrote for a print newspaper covering the swimming beat. Twenty-two years later, I still time most domestic meets by hand. Not because equipment is missing. The major pools in Hanoi and Ho Chi Minh City all have electronic timing systems for competition. The problem is that the data is generated but never archived, never standardised, and never published.

The result is a paradox. We have swimmers, we have performances, we have medals, but we have no long-term record from which to read those performances.

A generation of swimmers fades when nobody reads its data sheet.

Nguyen Thi Anh Vien is the clearest case. For about a decade, from 2026 to late 2026, she was the centre of every Vietnamese swimming medal table in the region. At the 2026 SEA Games in Kuala Lumpur she won eight gold medals, a figure Vietnamese swimming had never produced at a single Games. But when she announced her retirement in late 2026, most of the detailed data from that journey went with her. Splits, pacing models, the rhythm across each training year, stroke rate, weekly volume — all of it scattered across the notebooks of different coaches in different periods.

When the coach changes, the record disappears. When the record disappears, nobody can answer the simplest question: what actually produced those eight gold medals, and which part of it can be repeated?

Nguyen Huy Hoang is the opposite case in data terms. At the 2026 Asian Games in Jakarta he won silver in the 1500 metre freestyle in 15 minutes 01.63 seconds, according to the organisers' official results. It was Vietnam's first continental silver in a long-distance endurance event. The 1500 metre freestyle is a test of evenness: elite swimmers cover thirty lengths with a gap between their fastest and slowest length usually under two seconds.

But if you ask me which length he swam fastest and which length he faded on across his last four domestic meets, I have no data to answer with. And he is the most fully documented swimmer in Vietnamese swimming over the past decade.

Four data gaps that decide performance

First, pacing structure is not recorded.

In swimming the most important metric is not the finishing time but the slope of velocity decay. A world-class 200 metre freestyle swimmer typically goes out three to five percent faster on the first length than on the last. At domestic meets where I time by hand, the figure I usually record is eight to twelve percent. That difference does not come from talent. It comes from pacing, and pacing is coachable — but only if you can see it.

Without splits, a coach has one option left: tell the swimmer to go out faster, or tell them to go out slower. Both are guesswork handed down by word of mouth across generations.

Second, turns and underwater phases are not measured.

The first fifteen metres off the wall is the decisive zone in many events, especially backstroke and butterfly. At international level, major teams measure each swimmer's underwater time in every training session. At home, most meets record nothing. No measurement means no feedback. A swimmer knows their turn is weak only because a coach stands at the wall and says so.

In the same group, reaction time off the blocks is also left blank. In the 50 metre and 100 metre sprints, reaction time accounts for six to eight percent of total time. A sprinter whose reaction is a tenth of a second slower than a rival's loses nearly one percent of performance without any technical error in the lane itself. Without recording this metric, we cannot separate a slow swimmer from a slow starter, and therefore cannot know what needs fixing.

Third, stroke rate and distance per stroke are left blank.

Two swimmers with the same 100 metre freestyle finishing time can be running two entirely different movement economies. The first turns over forty-eight strokes per minute at two metres per cycle. The second turns over thirty-eight strokes at two and a half metres per cycle. The second is more economical at the same speed, and has a higher ceiling. This metric has an international name: stroke index, the product of stroke rate and distance per stroke, expressed per unit of velocity. It is free. It needs one person counting and one stopwatch.

We do not count.

Fourth, year-on-year athlete records do not exist.

This is the most serious gap, and the hardest to close. In football, a seventeen-year-old already has a GPS record for every session: distance covered, number of accelerations, high-speed distance. Football has tracking vests and leagues wealthy enough to fund them. Swimming has no equivalent device, but swimming has something even more favourable: everything happens along a lane of fixed length, under one clock, and can be counted by eye.

I have never met a young Vietnamese swimmer with a long-term record spanning ages twelve to eighteen. Most records survive only until the coach changes teams.

In 2026, when the pandemic halted the entire competition system, I was invited to review the physical data of a football club in Ho Chi Minh City. I read GPS data for twenty-nine players and found a clear pattern: high-speed running distance rose by roughly twenty percent in the two weeks before a muscle injury appeared. From that pattern I proposed splitting training load into four stress thresholds and tapering by threshold. The following season, the club reported roughly thirty percent fewer injuries than the previous season.

I tell that story not to talk about football. I tell it to show the gap. In that assignment I had twenty-nine records, each holding thousands of minute-by-minute data points. At the same time I was following a group of young swimmers in the same city, and I had exactly three durations per person: finishing times in three events.

One country, one city, one stretch of time. One sport has data. One sport has none.

The puberty barrier and the trap of discarding people too early

There is a fifth gap I treat separately, because its consequences do not sit in the results but in the people.

For female swimmers, the years from twelve to sixteen are when the body changes and performance often stalls for one to two years. That is a universal phenomenon, present in every country with a developed women's swimming system. What separates a good swimming nation from an average one is not avoiding that phase, but knowing who will come through it.

To know, you need a curve. That curve only exists if you measure the same person, on the same metrics, across several years. In Vietnam, when a fourteen-year-old girl stalls for two consecutive seasons, the decision is usually made on two data points and one conversation. Some swimmers have been cut from squads at fifteen and then swum faster two years later than the person who replaced them. I have witnessed at least three such cases in the past decade. Three cases do not make a study, but three cases are three signals — enough that I will not call it coincidence.

In swimming, injuries also have patterns. The shoulder carries the heaviest load in freestyle and butterfly; the knee carries the heaviest load in breaststroke. Without weekly training-load data, every injury looks like bad luck. With it, most look like the consequence of a coaching decision taken three weeks earlier.

The data gap is not a technical problem

There is a misreading I encounter often. Many people conclude that Vietnamese swimming is weak because equipment is lacking. That is not correct. Measuring splits needs no equipment. It needs one person with a stopwatch and one rule requiring publication. The cost is near zero.

The second misreading is that without data, analysis is impossible. Also not correct. Missing data is itself a fact, and it can be analysed. When a meet organiser does not publish splits for the national championship, it shows the system has never asked who the data serves. But I must be careful here: I can only say the two events are related, not that one causes the other. The causal chain linking missing data to stalled performance is short, but it runs through people: no feedback means no adjustment, and no adjustment means a swimmer repeats the same error for years.

There is one more point my model cannot measure. When a meet is held before a large, loud crowd, part of the variance in performance cannot be explained by any metric. I once watched a young swimmer go nearly four seconds slower than training form in a crowded final, then two weeks later swim exactly training form at an empty meet. Two data points do not make a conclusion. I logged it with a wide confidence interval and left it there, waiting for more data.

What to watch in the next round

Vietnamese swimming is in transition, and transition is when data is most valuable. One generation has stopped; another has not yet taken shape. In that gap, people tend to call a good result a surprise and a poor result a disappointment. Every shock has its own probability. We call it a shock only when we have not yet checked the sheet.

Three things I will time and log myself this season, regardless of whether the organisers publish them: four splits for every final involving young swimmers; the first fifteen metres off the wall; and a single continuous record per swimmer I follow, carried across meets.

A notebook does not replace a system. But in a sport where every movement happens along a line of fixed length, a notebook kept properly across years can do something I have never seen done here: separate a real talent from one lucky evening.

Most people look at the medal table to understand a Games. I look at the medal table to understand ten years that were never written down.