Monday 5th February saw Tyne Triathlon’s first Critical Swim Speed (CSS) test of 2018.

Many people will be asking, what is CSS, and what does it have to do with me?

The short answer to this is knowing your CSS and using to appropriately pace swim sessions will make you a faster swimmer. This is done by scaling various sessions/intervals based on CSS (much like a threshold pace in running, or FTP in cycling).

The more in depth answer is that CSS is the pace that a swimmer could hold over a 1500 time trial (yards or metres) as this gives a good approximation of lactate threshold speed. Obviously this is not an easy test to perform; an evenly paced, all out 1500 time trial is possibly one of the hardest challenges in pool swimming for even the most experienced swimmer. In order to make this easier and therefore a more repeatable method for assessing swimmers, the 400/200 time trial method is used. The key to a ‘good’ result is to evenly split both the 400 and the 200, with the results being as closely matched per 100 as possible. This is why in some cases faster time trial times lead to a slower result; the efforts may have been less well paced relative to one another.

The Benefits of CSS Training


  1. CSS is a pace that’s tough enough to develop your aerobic capacity but not so hard that it’ll take you days to recover. So you can improve your swim fitness and still have enough energy to go running or cycling (or swimming again).
  2. CSS is a race-specific training pace. It may not make you the fastest 50 or 100 swimmer, but it will train you to sustain a moderately high speed for longer distances.
  3. CSS training teaches you about pace awareness the hard way (which is usually the best way) Go off too fast and you’ll pay the price later. Ouch!

Thankfully we don’t have to work out how to then plan our training based on CSS results as we have Margarita to do this for us, however if you wish to know more about CSS there is a wealth of information online.


Remember that the CSS test isn’t perfect, if times seem to easy, the pace can gradually be increased provided it remains sustainable. Likewise if it is too hard the pace can be gradually reduced.

400 Yards Time 200 Yards Time CSS Result/100 Yards
Lane 1
Steve 4:27 2:13 1:07
Holly 4:54 2:20 1:17
Jill 5:02 2:23  1:20
David 5:21 2:33 1:24
Lane 2
Bella  5:42 2:50  1:26
Dave  6:02 2:53 1:35
Lane 3
Ollie  6:09 3:03 1:33
Chris 6:09  2:57  1:36
Ellie 6:03  2:58 1:33
Dave 6:18  3:02 1:38
Steve  7:05  3:30 1:48
Lane 4
Sarah  6:42  3:17 1:43 
Neil 6:38  3:14 1:42
John  6:59  3:21  1:49
Gill  6:55  3:25 1:45
Jeff  6:42  3:30 1:45 *
Lane 5
Angela 8:32 4:16 2:08
Zara 8:44 4:20  2:12

*The formula used to calculate CSS pace doesn’t work in cases where the 200 time trial is paced slower than the 400 time trial. Both the 400 and 200 should be well paced time trial results ( In this case the 400 time was increased to 7:00 to allow the formula to calculate.

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