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Improve Your Triathlon Swim Speed

One of the keys to improving your triathlon swim speed is to use your Critical Swim Speed to guide your training.

triathlon swimming

Critical Swim Speed is, in theory, the speed that you should be able to sustain indefinitely.

In practice due to local muscular fatigue the duration you can swim for at this speed will be determined by how good you are technically, how well or how long you can maintain good technique and how good your muscular endurance is.

As such it doesn’t directly relate to triathlon swimming performance. So two people might have the same critical swimming speed but be able to sustain this for different durations, and therefore their race performance will differ.

So critical swim speed is really a training tool.

Obviously improving swimming technique is something that will help the majority of triathletes swim faster.

Technique is a very individual thing and there are several means of having a 'good' stroke. Rather than go into this here please read our swim technique page

We tend to use critical swimming speed to help to provide guidance on swimming speed, to try to control intensity and make the training relevant to triathlon swimming.

We have seen many triathletes who train very hard in the pool be unable to convert the times they do in the pool to racing. This is usually because they perform reps in training at much faster speeds than they are capable of in the longer effort they are required to do in a triathlon race.

Knowing and using your critical swim speed helps to keep you on track training at the relevant speeds, but almost as importantly it keeps your stroke rate and technique much closer to that at which you will race.

How To Determine Your
Critical Swim Speed

To determine your critical swim speed you need to carry out two time trials. One over 400m and one over 200m.

Warm up and then carry out the 400m time trial first and after a full recovery, do the 200m time trial.

Try to pace the trials as evenly as possible, and do both from a push off the wall not a dive start.

Input your times into the calculator below to get your critical swim speed.

CSS Calculator:

CSS Calculator:

400m timetrial:

min sec

200m timetrial:

min sec

CSS Pace:


Using Critical Swim Speed

Let's say for a moment that your critical swim speed is 1:30 per 100 meters, and with that your ideal stroke rate is ~ 40 full strokes a minute.

If you are doing lots of training much faster than this then you will probably be increasing your stroke rate to achieve this, which will probably seem natural for those efforts. However when you try to do longer race efforts you will find yourself reverting back to your natural 40 strokes per minute, and swimming slower.

This may be ok for pool swimmers whose races are always short and require a lot of power and use a very high rate of carbohydrate metabolism to fuel them.

But for a triathlete wanting to perform over longer distances this is not effective.

So we use your critical swim speed to help control the intensity of the sessions. When used in conjunction with some monitoring of your stroke count per length this will help to increase triathlon swim speed more effectively.

Within this structure we use 3 main types of critical swim speed sessions.

Just remember that for all the examples we use time rather than distance. This is because a 400 meter rep for one triathlete could take the same time as a 200 meter rep for another.

Sessions To Improve Triathlon
Swim Speed

1. Under and Over

These sessions require you spend some time swimming a little faster than CSS and then a little slower. Not much on either side but enough to push you, but then allow you to recover.

So we could have:

Then repeat lots of times! How many would depend upon how good your endurance swimming is, how much hard swimming you want to do etc.

A good tip here is to try and maintain your stroke count for the whole session.

So if you are doing 75 m efforts in a 25 m pool and each length is taking 20 strokes at the beginning, try to hold onto that all the way through. If you start to go too far off this then you are becoming less efficient.

Stronger swimmers may want to change the durations of each effort, which is fine. A typical session for a few of our triathletes whose CSS is 1:14 per 100m is:

This set requires a high level of training and endurance fitness to be able to do this much volume at this intensity.

2. Short Repeats


These sessions require you to hit CSS but only for a short time, really encouraging you to hold good technique all the way through. To do this you have a long recovery but need to do lots of reps, so it is a session best done with plenty of time available.

Initially you will want to swim faster for the effort. DON'T! Keep to the pace and try to keep to your ideal stroke count for each effort.


This is essentially the same session as the technical repeats but with a few less reps and a lot less recovery, so it will hurt a lot more and will challenge your technique and fitness much more.

To enable you to do more reps you can split this into 2 sets of, say, 10 x 50 meters with a few minutes rest between them.

3. Long Efforts

These are long efforts at a pace just a little slower than CSS. You will be amazed to find this improves CSS more than trying to do lots of swimming above CSS.

Repeated 4 - 10 times depending upon your current level of fitness.

Just These Sets Then?

Of course not, there are a million (well, a lot) of ways of using critical swim speed, these are guidelines for you to begin thinking about. The crucial thing is the speed at which you train in swimming.

For those wanting to improve triathlon swim speed, it makes no sense to train super hard all the time at paces you cannot use in the competition environment.

 Be Coached By Intelligent Triathlon Training!

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