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What is CSS? Critical Swim Speed is based on the time you can swim a 1500m race in. CSS is then a measure by which you can train and improve your threshold, i.e. the 8.5/10 pace where it hurts but you can could hold it (for 1500m). This is super important to know for any open water swimmer or triathlete.

Side note: I managed to improve my CSS in a short space of time from 1.55 per 100m, to 1.35 per 100m. Remember everyone is different and it's not helpful to get into comparison either, unless you're the Olympic Champion over 400m there is always likely to be someone quicker than you. Relax and try to be the best version of yourself you can be! For me after 6 months off of swimming I will no doubt be back towards the 1.55 marker again, it'll improve with consistent and considered training!

Anyway, if you don't know how to find your CSS, try a CSS Test or CSS Time Trial.

What is a CSS Test/ Time Trial?

It is a 400m flat out effort, followed by a couple of minutes break with a few easy lengths in the pool to keep things flowing, then a 200m flat out effort.

You will need to warm up thoroughly, include some faster pacing when you go from the warm up to a build/pre-main/pre-time trial set (an example of a build set is below).

When you get to the flat out efforts make sure you pace yourself especially in the first 100 metres of the 400m, so don’t go off too hard, or you may fail in your attempt to finish.

Equally you do need to make sure you go hard enough. If you think you could’ve given it more at the end of a time trial, that’s probably something to learn from for next time.

Photo by Johnny Clow on Unsplash

Here is a session for you to try:

CSS Test Session:

Warm up: 500m

  • 200m front crawl/ 100m pull / 100m back stroke

  • 100m kick with or without board


  • Your call, keep it fairly short and just focus on drills that will help you personally with your own form during a harder effort.

Build set: 300m:

  • 3 x 100m build with 15s recovery Cycle through effort levels within the 100m as follows… (1st 25m easy, 2nd 25m steady, 3rd 25m CSS, 4th 25m hard)

  • 4 x 25m hard with 30s recovery

Main set: 650m

  • 400m time trial, pace it wisely especially the first 100m!

  • Take a breather, once breath is back, two lengths easy and on to the…

  • …200m time trial

Cool Down: 200m

  • 200m cool down mix of front crawl, breast stroke, back stroke and drills

Calculating Your CSS Pace You have your 400m and 200m times, use the CSS calculator to find out your CSS training times:

CSS Sessions:

Now it’s time to include a CSS session at least once a week in your training programme, if you’d like some sessions specifically designed and tailored to your ability level whether your a complete beginner, an improver, or you’re looking to progress into an international age group vest, give me a shout via email or WhatsApp me now, and I'll send a free session across for you to try.

If you want to chat about a monthly coaching plan to improve your CSS for OW swimming or triathlon training, book a call with me here now and we can chat about how I can help you.

Ian - TriClub . Proud to be a part of the Small Business Saturday 2020 cohort! #smallbiz100

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