Swimming Training Zone Chart

First, a name collision worth clearing up: in American age-group swimming, “Zones” usually means the regional championship meets and their qualifying time standards. This page is about the other thing — training intensity zones, the bands you write a set in. Calculate your CSS below, then read the chart against it.

The five zones, and what each one is for

The model this page follows has five intensity bands, separated by two physiological landmarks: the anaerobic threshold, which is what your CSS estimates, and VO2 max.

Zone	Purpose	Blood lactate	Heart rate	Set duration
1 — Aerobic capacity, low	base volume, technique, recovery	no rise, under 2–3 mmol/L	below ~140–150 bpm	40 min and up
2 — Aerobic capacity, moderate	aerobic development around threshold	transient rise, under 3–4 mmol/L	~150–160 bpm	around 30 min
3 — Aerobic capacity, heavy	threshold work, lactate clearance	high, 4–7 mmol/L	~160–170 bpm	10–20 min
4 — Aerobic power	oxygen transport and delivery near VO2 max	very high, 8–10 mmol/L	~170–190 bpm	3–10 min
5 — Anaerobic power and capacity	glycolytic capacity, tolerance to acidosis	above 12 mmol/L	above ~190 bpm	under 2–3 min

Those lactate, heart rate and duration figures come from Table 1 of a 2024 perspective article in Frontiers in Sports and Active Living — and it is worth knowing exactly what that is. It is not a study: the paper has no sample and no n, and the authors state that the table was built from the literature they had just reviewed plus “our own knowledge and experience”. Its own legend adds the population limit: the zones are “to be used, preferably, in populations of front crawl high-level swimmers”. None of the numbers above were measured on a masters or recreational swimmer, so treat the whole table as an expert proposal you calibrate against yourself. The heart rate column is the softest of all — read swimming heart rate zones before you take those as targets.

Turning the chart into a send-off

Here is the honest part: no governing body publishes a seconds-per-100 table. The only line with a measured basis is the threshold row, and that line is your own CSS. Everything above and below it is coaching convention, widely shared and not standardized. What follows is the common convention, with a CSS of 1:50 per 100 as the worked example:

Zone	Pace relative to CSS	With CSS = 1:50
1	CSS + 10 s per 100 or slower	2:00 or slower
2	CSS + 4 to +10 s per 100	1:54 to 2:00
3	CSS − 2 to +2 s per 100	1:48 to 1:52
4	CSS − 8 to −3 s per 100	1:42 to 1:47
5	CSS − 8 s per 100 or faster	1:42 or faster

Two consequences of that structure. Small CSS errors move every band at once, which is why the 400 and 200 test is worth swimming properly rather than approximately. And because the two-trial method reads slightly high, a threshold set built on a fresh CSS often feels like zone 4 for the first week or two — that is the test bias, not a fitness problem.

Rest is part of the zone

A swimming set is prescribed as an interval, not as a pace: 10 × 100 on 1:55 with a CSS of 1:50 gives you five seconds on the wall, and the rest is what keeps the effort in zone 3 rather than letting it drift up into zone 4. Change the send-off and you have changed the zone without touching the pace. That is why U.S. Masters Swimming teaches CSS work as an interval to leave on, not a speed to hit.

Volume distribution follows the durations in the first table. Zones 1 and 2 carry the bulk of the week because they can be sustained for 30 to 40 minutes; zone 5 is measured in seconds and behaves like a seasoning. To convert any swim you do into a pace you can place on this chart, use the swim pace calculator, and see the CSS calculator for the formula behind the reference pace.

This content is informational and does not replace coaching or medical advice.