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CSS Swim Pace Calculator

Critical Swim Speed Test

Calculate your training paces.

Calculate your swimming training paces and zones

When you look at your swimming program, have you ever wondered what the best pace should be swimming for different sets, for drills, for long intervals and sprints?

As no two athletes are the same, you could benefit most from individualising the paces to your ability or current fitness.

What are your individual training zones?
The CSS swim test can help you calculate your optimal swimming paces so that you get the most out of each training session.

Table of Contents

What is the CSS swim test?

The CSS swim test is a feedback loop we use to gauge improvements in aerobic fitness

The CSS swim test is a simple, effective and easily repeatable field test that is used to determine your optimal training zones for endurance swimming. The test can be performed with a coach, in a squad situation, or unsupervised. 
The data from the test is put into a formula to calculate the fastest speed at which you should be training to keep improving your aerobic capacity.
The Critical Swim Speed (CSS) is defined as the swimming speed that can be maintained continuously without exhaustion. This test can be used by coaches and swimmers as a measure of aerobic capacity and also to calculate training intensities.
The purpose of the test is to record your swim speed as a measure of endurance fitness so that it can be compared to future tests. The results of the test will help set your swim training paces from now until the next batch of testing.
While not appreciated by all coaches, the CSS swim test has been shown to correlate well with the swimming velocity corresponding to the onset of blood lactate accumulation (OBLA) and the maximal lactate steady state.
We like the test for its simplicity and repeatability

How to do the CSS swim test

Equipment required

  • a 25m or 50m swimming pool
  • a stopwatch.

The testing procedure

After a standardised warm-up, the swimmer starts each time trial in the water with a push start from the wall (no diving).
Record the overall time for the 400m TT (Time Trial) as well as each 100m split time i.e. your time at 100m, 200m, 300m and 400m.
Record the overall time for the 200m TT (Time Trial) as well as each 100m split time i.e. your time at 100m and 200m.

The recorded data is then submitted in the form below for analysis.

CSS Swim Test Protocol

WU: (Warm-Up)

200m swim long and easy
200m kick with a board
200m swim at a medium pace
100m kick with a board
6 x 50m building to race pace on 60 secs
Rest 1 min

MS: (Main Set)

400m Time Trial
Rest 1 min
200m swim long and easy
Rest 1 min
200m Time Trial

LD: (Loosen Down)

200m swim long and easy

What you will receive via email

Upon completion of the form below, you will receive an analysis of your 2 time trials as well as your training paces.

Swimming paces based on your CSS swim test results.

Warm-up and loosen down pace:

Use this pace for your warm-up and loosen down as well as anything denoted as “easy swimming”.
This is also your pace for doing drills and kicking sets.
Drills should always be performed slowly so that you can give 100% concentration on mastering the actions.

Aerobic Pace:

Use this pace for long intervals of 600m or longer, open water swims, paddles & pull buoy sets.
You should never feel out of breath when performing these sets. These are the swimming sets that build your stamina for CSS and T-Pace training so it is very important to control your aerobic pace very rigidly.

CSS Pace:

CSS swim sets are usually 100m, 200m, 300m, 400m or even 600m repeats.
The pace should not feel super hard at first, but you will feel fatigued towards the end of the set, so try to reign yourself in at the beginning in favour of holding an even pace all the way through the set. Examples of CSS swim workouts can be viewed on our swim blog posts

T-Pace: (Threshold Pace)

T-Pace swim sets of 100m, 150m, 200m, 250m repeats
The pace will feel hard, but you will get long rest periods to recover. The T-Pace sets are usually short so “Hang Tough”.
Be aware of keeping your style as strict as possible for as long as you can. If you feel you are starting to “thrash” the water and forcing your stroke, rather slow your pace by 5 seconds per 100m