Critical Swim Speed test results | 80/20 Endurance

Critical Swim Speed test results

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  • #10506

    Hi there!

    I had to do my CSS test today and I improved in both 400m and 200m. However, I seem to have paced the 400m rather badly as the time per 100m was slower than for the 200m.
    That now results in giving me a CSS that is 6s slower than before though my swimming in total improved.

    Is that intended and should I really follow the new CSS or should I redo the test and work on getting a more consistent result in both distances?

    Thank you!

    Matt Fitzgerald

    Your pace in the 400 SHOULD BE slower than your pace in the 200. After all, it’s twice the distance. Both time trials are intended to be completed in the least time possible, like races. In any event, given that your new CSS is slower yet you feel your swim has improved overall, it is worthwhile to repeat the test.


    Thanks Matt!

    That’s the thing, I actually can measure that the swimming has improved and yet the formula is set up to emphasize the gap between the 400m and 200m which results in an overall slower CSS.

    (old test 400m: 8:01 200m: 3:47 CSS: 2:07)
    new test 400m: 7:46 200m: 3:31 CSS: 2:08)

    So, both times improved and yet the CSS is 1 sec slower. If I would do my 200m in 4 minutes instead 3:31, the CSS would be at 1:53. That is a 15s/100m difference to the current result.
    As all workouts are based on the CSS, I’m having a hard time to understand that metric. Does that make sense?

    Matt Fitzgerald

    Now I see. It’s because you improved much more comparatively in the shorter effort. From our Intensity Guidelines for Triathlon resource:

    A mathematician will notice that the CV formula result is influenced both by the time and the delta between the two tests. Even if your total combined 400+200 time goes down from test A to test B, if the difference between the 400 and 200 times are greater in test B, your CV might actually increase. In this way, the CV test “punishes” the athlete for poor pacing.

    Some swimmers therefore may have a difficult time with the CV test. An alternative test is the 1,000 yard time trial. Swim 1000 yards (or meters) as fast as you can. Your average pace per 100 is your lactate threshold swim pace.


    Thanks again Matt! And sorry for that oversight, I have not seen that.
    I’ll go with the 1000m TT then – or just slow down the 200m 😀

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