If you don't know already, your CSS (Critical Swim Speed) is your threshold pace when swimming. It's roughly the pace you can swim a flat-out 1500m and is a single number which you can base all your training intensities from.
For instance in the squad I swim in in Perth, swimmers in lane 1 have a threshold pace around 1:50-2:00 /100m, lane 2 1:40-1:50 /100m, lane 3 1:25-1:40 /100m and lane 4 1:15-1:25 /100m.
If you have trained with a power meter on the bike you probably know your FTP (Functional Threshold Power) and running you might be aware of your threshold pace (the pace you can sustain for a race around 10km to 10 miles in length). CSS, FTP and threshold running pace are the equivalent thing in all three sports. Know them and you can train different energy systems accurately and track your progress over time.
So how do you find your CSS pace? Swim a 1500m timetrial? Well you could... but it would be mentally challenging to do and actually there's another way of doing it that gives more insight into your fitness:
The Standard CSS Test
After a thorough warmup and after a few key drills, swim a 400m time-trial. Pace it well and remember this is a flat out effort, you shouldn't finish and think "maybe I could have gone harder"!
If at all possible, have a friend, coach or lifeguard time your first 100m split of the 400m. As we'll come to later this will give you real insight into your pacing abilities. Record your overall time and also your 100m split.
Spend a few minutes recovering with some easy laps of freestyle until you feel you are ready for part 2 - a 200m time-trial. Again, well paced and a good hard effort. Record your time.
Note: if you are in a yard pool, swim 400yd and 200yd time-trials instead.
Swim an easy cool down to recover from your efforts.
Calculating Your CSS Pace
Armed with your times, enter your numbers into the basic CSS calculator here:
So how do you control your pace to swim at CSS? The secret is to use a Finis Tempo Trainer Pro set to beep at regular intervals such that you pace things out to be passing every 25m (or 25 yards) when it beeps. For instance, if your CSS pace is 2:00 /100m then set your beeper to 30 seconds. Get ahead of the beep every 25m and you are going to fast, behind the beep and you're travelling too slowly.
The key to CSS training is sustained speed with short recoveries. This is a little different to traditional master's swimming where the swims are faster but with much longer recoveries (sprint training).
An example CSS set is:
3x (100m + 200m + 300m) - all swum at CSS pace with 10 seconds rest after every swim
That's 1800m in total, suitable for swimmers with a CSS pace around 1:30 /100m. If your CSS pace is around 1:20 /100m, design sets around 2000m in length. If your CSS pace is around 1:45 /100m we suggest a set around 1600m If your CSS pace is around 2:00 /100m try 1400m in total
The key to these sets is sustained speed with short recoveries between swims. This will effectively develop your "diesel engine".
CSS isn't a concept that Swim Smooth invented they have certainly popularised it for swimmers and developed a whole system of focused effective training around it to help you achieve your potential in the water.
In essence it:
- Provides focused training to improve your distance swimming.
- Is quicker to recover from than many other training sets.
- Allows you train scientifically using a Tempo Trainer Pro.