Many swimmers often set out too quickly in races and training only to fade tremendously. 
With consistency in training, which includes working at chipping away at the CSS threshold sets, a swimmer can expect to improve 0.1 to 0.2 seconds per 25m every week or two. Doesn’t sound a like much of an improvement? 0.1 per 25m is equivalent to 0.4 seconds per 100m. After 20 weeks, that’s a whopping 8 seconds per 100m, or 2min 32 seconds over 1.9km half ironman.

Of course the rate of improvement will depend on the swimmers existing background and commitment and to consistency to training.


‘CSS’ stands for Critical Swim Speed – the same thing as lactate threshold. The technical distinction is that you measure lactate threshold by taking blood samples during exercise, which is difficult and intrusive to do in a pool environment.

Why do it?

The goal is to develop your lactate threshold. CSS based training sets are prescribed such that the swimmer is swimming at or about their lactate threshold speed for sustained periods of time. This stimulates the body to develop your aerobic system, which improves your distance performances.

CSS training not only builds your distance swimming “diesel engine” but also contributes enormously to Pace Awareness

Race Prediction

Once you have established your CSS time, this can also be used to estimate your race time whether this be 750m, 1.5km, 1.9km, 3.8km, 5km etc. Surprisingly with great accuracy too.




The Benefits of CSS Training

  • 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).
  • 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.
  • 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!


Including CSS sets into your swim training can help improve your sustainable speed and enhance your pace judgement. In addition to CSS training, it’s also important to strike a balance between speed, threshold and endurance workouts in order to meet the needs of your target races. Technique work and open water training are equally important too!


Example Session:
Pace Awareness Set: 1500m @ CSS Pace +5 seconds

After a 400m – 600m warm up have a go at this set.

The goal of the main set is to hold exactly the same pace for the 200m, 300m and 400m intervals as the swimmers did for the 100m intervals.

2x 100m + 1x 200m – take 20s rest between the 100s and 40s rest after the 200m

2x 100m + 1x 300m – take 20s rest between the 100s and 40s rest after the 300m

2x 100m + 1x 400m – take 20s rest between the 100s and 40s rest after the 400m

Sounds easy give it a go!!

Pace Awareness