Forgot Password?
Connect With Us Facebook Twitter YouTube Google+
Sat 24th Aug 2019
Critical Swim Speed made simple
Posted by: Editor
Posted on: Thursday 9th April 2015

Tags  Critical Swim Speed  |  CSS  |  Phil Mosley

Bookmark This  |  Print This Page  |  Send To A Friend  |  Post A Comment

A Brief Introduction to CSS Swim Training

CSS stands for Critical Swim Speed - a really simple concept that could improve your swim fitness, pace judgement and training motivation.

In this short feature Phil Mosley explains what CSS is, how it can make you fitter and how to test your CSS. He'll also give you some sample CSS training sessions to take home.

What Is CSS?

CSS is the pace at which you'd currently swim a 1500 Time Trial (in yards or metres). There's nothing complicated to worry about - it's simply an effective way to prepare for race distances of 400 and above. Here's why:

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. Thus, 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!
  4. Thankfully you can test your current CSS pace without having to swim a solo 1500 Time Trial. See below for instructions.
  5. Once you know your CSS pace, you can use a Finis Tempo Trainer Pro to help you train. It's a small beeping device that attaches to your goggles. Dial in your CSS pace and it'll happily beep every lap so that you can maintain perfect pace.

How To Test Your CSS

To test your current CSS pace you need to swim a 400 and 200 Time Trial within the same session (see CSS Test Workout below). Ideally, get a friend or coach to time you and record your 100 splits and strokes per minute. Failing that, simply record the 400 and 200 times yourself. Once you're done, enter your 400 and 200 times into this CSS CALCULATOR.

CSS Test Workout

Warm Up

  • 300 easy freestyle - 200 fins as 50 choice drill, 50 freestyle - 4 x 50 freestyle (25 fast + 25 easy) +10secs rests
  • 4 x 100 freestyle (+20secs rests)/ Do these 100's at what you perceive to be the AVERAGE pace that you can sustain for a 400 Time Trial.

Main Set

  • 400 time trial
  • Take 5 to 8 minutes easy swimming/stretching. Feel fully recovered, then:
  • 200 time trial

Warm Down

  • 100 easy choice of stroke

CSS Sample Workouts

Once you've worked out your CSS pace, the training possibilities are endless. You could start off by trying these four simple workouts. You can shorten them if you're not quite ready for 2000 metres or yards yet. Don't forget to include a warm up (400-800m/y) and warm down (100-200m/y) too.

  1. 20x100 with 15secs recoveries. All at CSS
  2. 10x200 with 20secs recoveries. All at CSS
  3. 5x400 with 30secs recoveries. All at CSS
  4. 3x600 with 45secs recoveries. All at CSS


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!

For more information about CSS training check out the SwimSmooth Training System.

Phil Mosley is a top-ten Ironman finisher and five-time national UK age-group triathlon champion. He is the current Coaching Editor of Triathlon Plus magazine and has written hundreds of features for titles including Cycling Plus and Cycling Weekly. He has an honours degree in Sports Science and 10-years experience as a triathlon, running and cycling coach. His coaching company is called

Twitter: @phil_mosley and @my_pro_coach.

Related Articles
© Bob Foy
Don't think you need to use your legs in a...
Posted on: Tue, Feb 3, 2015 at 14:51
Taking an end of season break sounds easy, but...
Posted on: Tue, Nov 25, 2014 at 12:30
#MyChallengeUK – Phil Mosley Phil Mosley,...
Posted on: Tue, Aug 19, 2014 at 14:30
After "entering several" iron-distance...
Posted on: Tue, Aug 5, 2014 at 13:38

Have Your Say