Training guide

CSS test: your critical swim speed

CSS, critical swim speed, is the pace you can hold for a long time in the water. With two swims and a simple sum, you get a measure to set the pace of every swim workout.

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How the test works

  • Warm up with 400 metres easy.
  • Swim 400 metres as fast as you can evenly, and note the time.
  • Swim easy for five minutes.
  • Swim 200 metres as fast as you can evenly, and note the time.
  • Cool down with 200 metres.

How to work it out

CSS per 100 metres is the difference between the times, divided by two: (400 m time − 200 m time) ÷ 2. If you swim 400 metres in 7:20 and 200 metres in 3:30, it is (440 − 210) ÷ 2 = 115 seconds, so 1:55 per 100 metres.

A test you can trust

  • The 400 metres should take more than twice the 200 metres time, but not much more. If the 200 is slow compared with the 400, you held back.
  • Don't start too hard: an even pace gives a fair result.
  • Repeat the test in the same pool, so it can be compared.

What TriQuest does

  • Plan a threshold test puts the CSS test in your calendar, and the workout goes to your Garmin with the test's steps.
  • The times are read from the swim you recorded, and your new CSS updates the pace of your workouts when you approve it.
  • Every swim workout has a pace per 100 metres from your CSS, in the pool and in open water.

Common questions

Common questions about CSS

How often should I do a CSS test?

When your swimming has changed noticeably, for example after a few months of regular training.

Can I do the test in open water?

You can, but in a pool the distances are exact and the result more reliable.

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