Critical Swim Speed
Your Critical Swim Speed (CSS) is the predicted pace you could currently swim a 1500 time trial. The 400 and 200 within your test are used to calculate your CSS.
Once you have completed your swim test, you will need to update your threshold settings in TrainingPeaks.
If you see the error message 'Your 200 pace is slower than your 400 pace!' when entering your swim times into the CSS Calculator it means your pace over 200 was slower than over 400.
During both parts of the test, you will be utilizing both your aerobic and anaerobic systems. The test is designed to determine what you can swim aerobically as this is a sustainable effort. The anaerobic part of your test is ignored. (The CSS test assumes you are unable to swim the whole 200m anaerobically).
The test establishes the difference between your 400 and 200 times and predicts your 1500 pace from that. And assumes that your 200 will be swam at a quicker pace than 400.
To calculate CSS, the 200 time is subtracted from the 400 time and the result divided by two to get your 100 pace.
However, your CSS is reliant upon the relationship between the two parts of the test and the speed itself. And to reliably calculate your CSS, the calculator needs a faster-paced 200 than 400.
Factors that can result in a slower pace over the shorter distance:
- Fatigue if you are a new swimmer, or returning after a break.
- Not sufficient recovery between the intervals.
- Busy lane, or any other external influencing factor.
If you have a good idea of your estimated Swim CSS enter that for now. However, if you find your sessions feel too easy or hard at the prescribed paces, or your planned v completed swim TSS is a long way off, you may need to retest earlier than scheduled.
If unsure, please email our coach support team (from the Email the Coach button at the top).
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