Swim LT pace: How to determine CSS (Critical Swim Speed)

CSS (Critical Swim Speed) in Swim is equivalent to FTP (Functional Threshold Power) in Bike and FTp (Functional Threshold pace) in Run.

Since P of Power and p of pace overlap, for the sake of convenience, the bike is distinguished from FTP, and the run is distinguished from FTp.

This CSS has a different definition from the FT pace of the swim at 1000 m TT (Time Trial).

Here, I will calculate CSS according to its definition based on my current swim ability.

Definition of CSS

CSS is the speed at which a threshold pace of 100 m is estimated from the time and time difference between 400 m TT and 200 m TT.

Quantitatively, it can be obtained as follows.

CSS [m/min] = (400 [m] – 200 [m] ) / ( 400mTime [min] – 200m [min] )
CSS [min/100m] = 1 / CSS [m/min] x 100

When qualitatively interpreted,It shows the speed when swimming 400 meters after swimming 200m, and the person with less difference between 0-200m and 200-400m becomes faster.

A:400m 8:00、200m 3:59, B:400m 7:41、200m 3:39, with this calculation, B is the same CSS even though both 400 m and 200 m are faster than A by 20 seconds.TSS:2:00/100m

A:400m 8:00、200m 3:59・・・TSS:2:00/100m
C:400m 8:00、200m 3:49・・・TSS:2:06/100m

The definition of the speed zone is as follows.

Warm up Zone 89-90%
Grey Zone 91%
Endurance Zone 92-94%
Tempo Zone 95-98%
Threshold Zone 99-106%
Supra threshold 106-119%
All Out Effort 120% and over

Calculation of CSS

will calculate it concretely in my time.

As usual, I have not done a time trial of 400m and 200m firmly … · · ·
(Even so, I managed to locate it because it is preferable to swim well as it is.

400m ・・・7:41→7.68333min
200m ・・・3:48→3.80min


CSS[min/100m]=1/51.5 x 100 =1.94165 →1:57(Rounding off of56.5)

My CSS will be 1: 57.

By the way, it can be easily calculated with this calculation site.
Swim Smooth CSS Calculator

Calculation of speed zone based on CSS

I also calculated the speed zone.

Warm up Zone(89-90%) ======>2:11-2:10
Grey Zone (91%)============> 2:09
Endurance Zone (92-94%)=====> 2:07-2:04
Tempo Zone (95-98%)========> 2:03-1:59
Threshold Zone (99-106%)=====> 1:58-1:50
Supra threshold (106-119%)====> 1:50-1:38
All Out Effort (120% and over)===> 1:38>

Next time I will try to verify variously using this result.

See you soon.

I am referring to it.

GTN Presents: What is Your Critical Swim Speed? (And How to Increase It)

How to Use Critical Swim Speed Training

How to Best Calculate Swim Zones in TrainingPeaks


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