CSS Test Sheet

The test

CSS PACE PER 100

(400 time − 200 time) ÷ 2

CSS as a speed

200 ÷ (400 time − 200 time) m/s

Protocol

both MAXIMAL, same session, ~5 min easy between

Example: 6:20 and 3:00

(380 − 180) ÷ 2 = 100 s per 100

That 400's own pace

380 ÷ 4 = 95 s per 100

Longer aerobic sets

CSS + 2 s (convention, adjustable)

Shorter faster sets

CSS − 2 s

⚠ CSS is SLOWER than 400 pace

if it is not, a trial was not maximal

⚠ Test in the pool you train in

short course is faster — more push-offs

Test history

Today's test

Name

Date

Pool length

Warm-up done

400 TIME

Recovery taken

200 TIME

CSS PER 100

400 pace for comparison

Gap

Both felt maximal?

Next retest date

Doing the test properly

• Warmed up fully before the first trial
• Both swims genuinely MAXIMAL — the gap is what is being measured
• About five minutes of easy swimming between them
• Same session, not two different days
• Pool you actually train in
• Rested and fed similarly to any other retest
• Cleared with a clinician if there is any reason to check first
• Not alone in open water
• Retest booked for four to six weeks' time

The gap is the measurement

CSS depends entirely on the DIFFERENCE between the two times, not on either one. A hard 400 followed by a half-hearted 200 gives a falsely fast CSS; a conservatively paced 400 gives a falsely slow one. Both trials have to be genuinely all out or the number describes nothing.

Slower than your 400, on purpose

A 400 is swum partly on energy you cannot keep spending. CSS estimates what remains when you cannot — so it lands a few seconds per 100 slower, and that is the correct answer rather than a disappointing one. Training at 400 pace and finding the second half of a set collapsing is a pacing problem being read as a fitness problem.