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Training using CSS (Critical Swim Speed). Be specific with your training and get on the fast-track to better results!

Having just taken the new Wednesday Do3 Swim Squad (click for info) through their CSS test, I thought it was worth explaining what CSS is and why it forms the cornerstone of our squads training. I will try to keep it fairly simple…..

Just what is CSS? CSS stands for Critical Swim Speed. Its is usually given as a pace per 100 meters i.e. 01:45 (1 minute 45 seconds) per 100m. 

Why is it so important? Your CSS pace is an estimation of your lactate threshold speed. This is the speed at which the level of lactate in your blood starts to rapidly increase. Think of it as the line at which your body switches from being an aerobic to an anaerobic machine (this is grossly simplified but I did say I'd keep it simple!). CSS tests are also an excellent way of 'benchmarking' a swimmers current ability – hopefully seeing an upward trend with each test!

Aerobic vs Anaerobic. Almost all of the events that swim squad members participate in are aerobic in nature. This means that your body is taking in enough oxygen to meet the demands of the exercise being performed. When you 'go anaerobic', things start to change substantially and you will become fatigued very quickly. 

Become more efficient. Training at or around CSS pace will make you a more efficient swimmer. Your threshold/CSS will effectively shift upwards meaning that you will be able to swim at faster speeds and still remain aerobic (or swim the same speed but with less effort).

CSS Testing. Swimmers are asked to swim two time trials at a maximum effort, one of 400m and then one of 200m. Your CSS speed per 100m is then calculated using the two swim times and a formula. 

Sometimes all is not as it seems…. The CSS formula looks at the relationship between the two swim time results. Provided the swimmer is sufficiently rested for each time trial, the 200m swim should be at a faster average pace than the 400 (because they have been completed at maximum effort). The formula looks at the 'drop-off' in pace between the 400 and 200m times. Having a smaller drop-off gives an indication that you are more aerobically conditioned than someone who has a larger drop-off in pace, or a diesel engine rather than a petrol! Due to the relationship between the 400 and 200 times being taken into account, sometimes a swimmer who has faster overall results can have a lower CSS speed (see the example on the chart). This means this swimmer needs to spend time working on their endurance to better develop that diesel engine. 

How using CSS effects training sessions. Once we know a swimmers CSS pace we can plan sessions that take this into account. The swimmer will be required to swim intervals based on their CSS, for example "SWIM 100m at CSS+2". This means at if the swimmers CSS pace is 01:45 per 100 meters they should swim the interval at a pace of 01:45 +2 seconds (so 01:47). Training like this ensure that the sessions are accurate and specific to the individual - quality training. 

Lane seeding. When swimming in the squads, swimmers are usually 'seeded' based on their CSS pace. This means that they swim with others of a VERY similar ability and have people to support and motivate them in the lane (as well as being 'motivated' by coach on poolside of course!). 

Sounds complicated. How do you keep track? We use a great little device called a 'Finis Tempo Trainer' (see the picture above). The Tempo Trainer can be set to bleep at timed intervals and this is usually set to bleep per length. The swimmer with the tempo trainer simply has to make sure they hit the wall on the bleep, this makes sure they are bang-on pace. The Tempo Trainers have other functions which we can look at another time but they are great little gadgets that really keep you focused during your swim sessions (I can supply these for £32 (RRP £43) or click here to buy on Amazon).

Pacing. When I run CSS tests, I also time the swimmers first 100m split during the 400 time trial. Due to the competitive nature of most swimmers and triathletes, the word 'test' in their mind suddenly becomes 'race' and as such go off like a bat out of hell only for their pace to die as they get further into the swim. This poor pacing nearly always leads to a slower overall swim than if they had more evenly paced things. If you look at the chart above you will see how fast some swimmers went off over the first 100m. There is even a column which shows how far ahead they would have finished had they kept that initial 100m pace up! Being good at pacing is an important skill to have, particularly during long events. We work on pacing skills during the squad sessions. 

Wrap-Up. I hope by now that you get the gist of what CSS is about and why we consider it to be so important. No longer should you just go out and swim 'junk' miles. Junk miles=junk training. Be specific with your training and maximize your time in the pool.

SWIM SMOOTHI use 'Swim Smooth' methods when coaching, many of which I learnt while training at Swim Smooth HQ in Perth, Australia. I am pleased to say that I was selected by Swim Smooth to become one of their certified coaches in the UK and I am currently undergoing their certification process. Thank you to the guys at Swim Smooth for the spreadsheet calculator shown above. Click Here to take a look at the Swim Smooth page on CSS training. 

If you want to find out more or join our Swim Squads click here.

other reports by: David Knight
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