The 200 and 400 m swim test, and what Leo does with it

What the test actually measures

Two efforts of different lengths, both maximal, draw a line: distance against time. The slope of that line is a speed you could theoretically hold for a long while, and the gap between the line and your actual 200 m is what your anaerobic store contributed — the part you cannot spend twice. That is why one time trial is not enough. A single 400 m tells you how fast you swam 400 m; it cannot separate your sustainable engine from the bit you borrowed, and those two answers can be a long way apart in a pool.

How to run it properly

Warm up thoroughly, then swim the 400 m all out. Recover fully — several easy minutes, not thirty seconds — then swim the 200 m all out. Same pool, same day, same session. Push off the wall the way you always do rather than inventing a racing start, because the test has to resemble the swimming it will prescribe. Do not do it at the end of a heavy week, and do not do it the day after a long ride: a tired test gives you a slow critical speed, and a slow critical speed makes every session that follows too easy.

Why 200 and 400, and not any two distances

The two efforts have to be far enough apart in time for the slope to mean anything — about a minute of separation is the practical minimum. Two distances that are too close give you a line drawn through two points that are almost the same point, and a small timing error then swings the answer wildly. The 200/400 pair is the pool's standard for exactly this reason: it is a big enough spread for most swimmers, and short enough that both efforts can be genuinely maximal in one session. A 100 m paired with a 400 m works too, but the 100 leans so hard on the anaerobic side that the line gets fragile.

From one number to five training paces

Your critical speed is the anchor, and the training bands sit around it: easy, aerobic, threshold, hard repeats, and short sprints. One detail decides whether those bands are usable — they are percentages of the SPEED, converted back into a pace, not percentages of the pace. The two are not the same operation and they diverge most where the band is widest. Water is also not air: drag grows with the square of speed, so a swimmer's usable range is compressed compared with a runner's. Easy swimming sits a handful of seconds per 100 m slower than critical speed, not half a minute, and a band built by analogy with running zones puts your easy sets so slow that the session stops training anything.

What Coach Leo does with it, and what it does not

When your target race has a swim leg and no critical speed is on file, Leo puts the two-distance test into the plan itself rather than waiting for you to think of it, and prescribes steady aerobic swimming until the test exists. Once it does, your sets come out in metres with a target pace per 100 m for each one, and they export to your watch so you are not memorising them on the pool deck. Retest every couple of months or after a block, because the anchor drifts. What Leo does not do: read a critical speed out of a random Strava swim, coach your stroke from a video, or estimate an overall triathlon time. The detail of the rest of the week is on Coach Leo for triathletes and on the format pages, for instance half distance.

Frequently asked questions