Vietnamese Swimming Data: When an Empty Record Is Itself the Data

In July 2026, at the My Dinh Water Sports Palace, on the second day of the national swimming championships, I counted 38 fully populated split times out of more than 400 swims logged that day. The rest of the notebook was filled with names, events, final results, and a blank stretch the exact length of a 50-metre pool.

I knew who touched first. I did not know why. Thirty-eight out of more than four hundred - less than ten per cent. That blank was what I took home, not the medal table.

Three years later I still keep the habit of logging the "empty-record rate" of every meet I follow. It does not measure a swimmer's speed. It measures the distance between a result existing and a result being readable. In swimming, that distance is larger than in any sport I have worked.

When a data field is empty, the emptiness has to be read as an event, not as a gap to be filled.

Context: why swimming is harder to read than football

I came out of football data. After years analysing the V-League and European leagues, I grew used to every match leaving a thick trace: passes, distance covered, xG, PPDA. Football enjoys a structural advantage - almost every action is captured on camera, and anyone patient enough can reconstruct a match from video.

Swimming is different. Swimming leaves no natural trace. The final result - a number in seconds - is the only output that a typical Vietnamese meet is obliged to record. Everything that produced that number, from reaction time at the start, to the underwater angle, to turn control, to stroke rate, to distance per stroke, to the pacing between segments - all of it vanishes the moment the official hits the watch.

Split time is the minimum. A 100-metre freestyle swimmer may go out fast over the first 50 and collapse over the second, or the reverse. With only a final time, two swimmers touching in the same 52 seconds are identical records on paper. In reality they are two different stories, two different points of physical failure, two different technical problems. You only see them if you have splits.

In developed swimming nations this is not a problem. World Aquatics runs its events with automatic per-50-metre recording, and that data is published almost in real time. American, Australian, Chinese swimmers walk into a press conference with a splits sheet in hand - something Vietnamese swimmers often wonder about when they ask teammates how their third 50 actually went.

The problem is not equipment. The problem is operating habit.

I have spoken with more than a few meet organisers at home. The common answer is: "Recording the final result is already exhausting." That is true operationally, but it produces a long-term consequence few people name: the entire Vietnamese swimming analytics effort is forced to run on data that is too coarse. From there, every inference about tactics, about endurance thresholds, about an athlete's developmental stage, lacks a base. The analyst is forced to reason from a single data point - precisely the figure they know is insufficient.

I call this paradox the systemic blank. It is not the fault of any single meet. It is the fault of a sport that has never asked what it needs to record before the race begins.

Analysis: the seven data layers a swimming record needs

When data is coarse, an analyst has two choices. Either accept saying little, or drag foreign models onto a base of data they do not fit. Both have a cost. I chose a third path: draw the full structure of an ideal swimming record, then check which layer Vietnam is missing. The gap between blueprint and reality becomes the priority map.

The first layer is technical. A minimum technical record includes reaction time at the start, the underwater time over the first 15 metres, turn time, and finish time. In butterfly and freestyle the keyword here is the underwater phase - the ability to hold speed after leaving the wall through the dolphin kick. Leading nations treat that 15-metre segment as a discipline in itself, coached separately and measured separately. In Vietnam, almost nobody records it.

The second layer is speed and stroke efficiency. Three key metrics: stroke rate (cycles per minute), distance per stroke, and the stroke index - the product of the two. The stroke index tells you whether a swimmer is buying speed by spinning the arms faster or by pulling water further. These two routes lead to completely different training problems: the spinner needs technical efficiency, the glider needs strength and endurance. Without stroke data, a coach can only teach by feel.

The third layer is pacing. This is the layer almost entirely absent in Vietnam. A 400-metre race needs to be read across four 100-metre segments, and the question is always: which segment was fastest, which collapsed, and by what percentage. In international swimming, people speak of the "negative split" - swimming the second half faster than the first - as a marker of good endurance and masterful pacing. In Vietnam, that term barely exists in everyday coaching vocabulary.

The fourth layer is result positioning. A time only means something inside a reference frame. A full frame includes the world record, the all-time list, the current-season ranking, and the Olympic qualification standard. These four layers give four different answers. A swim may break a reserve Olympic cut while still sitting outside the season's world top 50, meaning a berth may still not open. With domestic results alone, one easily mistakes an impressive national time for an internationally meaningful one.

The fifth layer is meet context. The same time at a junior meet and at a national championship does not tell the same story. The same time in an Olympic year and the year after does not either. The Olympic cycle has four kinds of years: Olympic year, adjustment year, accumulation year, and sprint year. Reading a performance without knowing which kind of year an athlete is in is reading half a sentence.

The sixth layer is regulation and sports medicine. Swimming is a sport with a dense rule framework: the 15-metre rule at the start and turn, the rules on the dolphin kick in breaststroke, the rules on start equipment in backstroke. Any technical change must be checked against that framework before entering training. Alongside sits the anti-doping layer - a field in which swimming is especially sensitive because of the sport's own history.

The seventh layer, and the one most neglected in Vietnam, is the career curve. Swimming is a sport where peak age arrives early and the puberty threshold hits hard. For women, puberty often brings structural body changes that can temporarily slow performance, and if it is not managed correctly it can erode an entire generation of talent. For men, peak age usually arrives later and lasts longer. Reading a junior result without knowing where the athlete sits on that curve is a systemic error.

Seven layers. In a notebook at My Dinh, I had the first layer in a very thin form, and the rest nearly blank.

The counterintuitive angle: an empty record is not a failure, it is a diagnosis

There is a wrong way to read this that I once fell into. When data is empty, the analyst's reflex is to fill it. Drag a foreign model over. Take an international meet with full data, line it up against named Vietnamese swimmers, and derive conclusions that sound scientific.

That approach is wrong at the foundation. It assumes two swimming nations run on the same logic. They do not. In a data-rich nation, analysis means thinning noise to find signal. In a data-thin nation, analysis means finding the missing structure to know what to measure first. These are different jobs in essence, and mixing them produces conclusions that are neither verifiable nor free of fake scientific flavour.

I once treated models as scripture. Now they are only a compass - but without them, we get lost.

This leads to a counterintuitive consequence: an empty record is not an analytical failure. It is the most accurate diagnosis analysis can offer. When I say only 38 of more than 400 swims had splits, I have said something more important than any conclusion about a specific swimmer's speed. I have said that this swimming nation is operating at the lowest possible data tier that still produces a ranking.

Splits are not wrong; swimming itself is irrational. After 2026, I learned to count the irrationality too.

And there is one more point I want to state plainly. In the history of swimming analytics, the biggest turning points never came from discovering a new metric. They came from changing what people recorded. When automatic split recording arrived at major meets, the entire debate about pacing became possible. When underwater cameras became common, an entire discipline of underwater coaching was born. No metric achieves that if the data does not exist first.

In Vietnam, the question is not "which metric is best". The question is "what do we have to measure first".

When the stands are empty, every model collapses. I rebuild from the burnt wreckage of data.

The first thing rebuilt is not the model. It is the measurement infrastructure.

A signal for the next cycle

I do not believe one article can fix a data culture. But I believe in one specific breaking point.

A national championship can begin recording full split times for finals. It is a small operational decision, near-zero in cost if an electronic timing system is already in place, but its long-term consequence is large. It moves Vietnamese swimming from reading results to reading races. The moment splits exist, coaches start asking why the third segment was slow. When that question appears, demand for the next layer of technical data emerges on its own. That is the mechanism I trust, not a top-down one.

I will keep logging the empty-record rate of every meet I follow. If that number starts to fall, I will know this sport has changed direction. If it stays flat, I will know I still have work to speak about for years to come.

A notebook does not fill itself. But a blank named correctly is no longer a blank.