Critical Swim Speed calculation and paces

Calculate your Critical Swim Speed (CSS) to monitor your fitness progress and to set the optimal swim pace training zones for you.

We all know with Cycling and Running it's important to make sure you're following the correct Training Zones for you to maximise your aerobic training, and avoid over-reaching in your workouts.  Over-Reaching in this sense of the term isn't referring to your technique, but it's actually how much stress you are exposed to through the workout.  Over-reaching can lead to an accumulation of fatigue and a breakdown in your swim stroke.  Train in the appropriate zones to ensure this doesn't occur.  Good swimming fitness enables you to swim for longer with correct technique, and eventually at a faster pace.

Thanks to Paul Newsome of Swim Smooth who worked closely with his athletes on their CSS, and popularised it's use, as well as finding a quick and easy way to calculate it, we have a very simple but highly effective way of using it in our own training. 

What is Critical Swim Speed (CSS)?

Your CSS is a thoeretical marker by which you should be able to swim continuously in a repeating set without reaching excessive exhaustion.  In terms of distance it's approximately 1500m, or maybe up to 2000m for faster swimmers.  Training to your CSS makes sense for Triathletes as we are often swimming distances further than 1500m, so we can get a reliable estimate of our race day swim time.

Swimming a 1500m Time Trial will have you right at your Lactate Threshold, so it makes sense to use this time as an reference point to use a pace either slightly faster or slightly slower than your Lactate Threshold, and with rest intervals either longer or shorter respectively, in order to seek aerobic gains.  If you can improve your swimming speed at Lactate Threshold, or stay there for longer, then your pace will get faster and you will be quicker in the water.

As you approach a key race in your season you will want to introduce specific CSS paced workouts in order to see those gains.

Test for your Critical Swim Speed

This testing method may not be perfectly representative of your true CSS, but it's going to be pretty close.  It's a test that can be easily done at your local pool, doesn't need any testing equipment (other than your watch or a pool clock), and is simple enough to repeat every 4-12 weeks.

The test consists of two all out swim TT's - 400m and 200m, in that order.  You will need to have a suitable warm up before the 400m test, and a good amount of recovery after it, before you hit the 200m test.  Try to swim the tests as evenly as you can, so don't start too fast and slow down as you go.

Click this link to be taken to our CSS test workout

Calculate your Critical Swim Speed

This is a very simple process and we even have a CSS Calculator built into the membership site.

Head to your Dashboard and click on 'Resources' then 'Calculators'

Select the Swimming Calculator

Enter your 400m and 200m TT times, and the length of the pool you swim in

Once you click Calculate you will see your CSS pace and the time this equates to per length of the pool you will swim in.  If you use a Tempo Trainer you can input this time so you know the pace per length for your CSS pace, or alter the time if you want to swim faster or slower than your CSS time.

How to train to your CSS

You should be able to train quite comfortably at your CSS pace for a basic aerobic set, such as:

20 x 100 at CSS with 15s recovery

10 x 200 at CSS with 20s recovery

5 x 400 at CSS with 30s recovery  

3 x 600 at CSS with 45s recovery

These are great aerobic fitness sessions, and you will find you will quickly develop your swimming with these.

If you want to push yourself a bit, and try to improve your speed you can try variations of these, such as:

10 x 50 at CSS - 10sec paddles with 10s recovery

10 x 100 at CSS - 5sec 10sec pull and paddles with 10s recovery

20 x 25 at CSS - 10sec fins with 10s recovery

3 x 800 at CSS - 5sec pull paddles with 1min recovery

A quick way to figure out how these paces compare to real life triathlon speed is to think about them this way:

CSS + 5-8sec/100m = IRONMAN swim pace

CSS + 3-5sec/100m = IRONMAN 70.3 swim pace

CSS/100m = Standard Distance Triathlon

CSS - 3-5sec/100m = Sprint Distance Triathlon

The cool thing about CSS training is there's not really a way you can mess it up.  Some people will find they do better with shorter intervals, some will do better with longer intervals.  Find which one works for you and settle into it.  Be patient and you will see the gains come.