Critical Swim Speed (CSS) TEST

Ideal for IRONMAN, IRONMAN 70.3 athletes or any athletes looking to evaluate where their swim ability, the CSS test is a fundamental measure in swimming. Just like FTP power on the bike, or FTPa threshold pace on the run. Your CSS pace acts as a threshold. The test helps coaches and swimmers in two key areas.

1) Where you are ‘at’ performance-wise or a benchmark of your current swim ability, and
2) What is a suitable pace for a threshold swim.

The first point is somewhat subjective. As we know, on any given day your performance can vary, especially at different points of the season where your overall training load may be higher or lower. But, that in turn also provides a pointer. Whether you benchmark faster or slower it will help you set a marker for your threshold swims at that time in your training cycle.

The second point is important for pacing. As with all disciplines in endurance sport, applying the right intensity at the right time is an important skill. Knowing your threshold pace gives you a figure on which to base your intervals. If your interval asks for a threshold effort, CSS effort, or an effort around 85% then this will be your threshold pace. For a long IRONMAN swim, you’ll want to be pacing yourself a lot slower.

THE TEST

We could ask you to simply swim 1500 as fast as you can and time yourself. If done correctly that would give you a great indication of your CSS pace. If you think that sounds like a fairly horrible task then you’d be right, it also requires you to pace the entire 1500 perfectly and count your laps perfectly too. So, instead, we extrapolate the times of two easier time trials. A 400 ‘all out’ timed swim, followed by a 5 minutes rest interval. After this, another ‘all out’ time trial but this time 200.

By taking the 200 pace and correlating it against the 400 pace we can establish a pattern of how much your pace slows down as you go longer.

It does not matter is you use a pool built in yards or meters. The test remains the same and the results is simply a pace per yards or pace per metres.

Key Part

The scientists have plotted the results of many 400 and 200 tests over many athletes. They have formulated an equation to estimate your threshold speed / CSS Pace using just a 400 and 200 test. Easier mentally, easier physically, easier to pace.

It should be noted that the formula is based on your fastest possible 400 and fastest possible 200. The reason for having a long break between is so that you completely recover from the 400 prior to doing the 200. You could actually do them on different days if you wanted, but a good rest interval of 5 minutes or so between the 400 and 200 should be enough.

The Caveat

The test does fall apart a little if your pacing is not spot on. Like we mentioned before, the equation is based on the 200 and 400 times, and the difference between the two. You obviously slow down pace between the 200 and 400 TT,  but how much do you slow down? That’s what the CSS time is extrapolated on.

If you nail an amazing 200 time, but pace your 400 poorly. That slow down in pace is going to be greater, which gives you a worse CSS result. It is perfectly feasible that an athlete beats their previous 200 time by a lot, beats their 400 time by a little and suddenly finds their CSS test result worse than it was before …. because the difference between the two times was greater than before.

In a CSS (Critical Swim Speed) test, the 400 pace is typically about 3–4 seconds per 100 slower than the 200 pace. This 3–4 second gap per 100 is common for trained triathletes and swimmers. Larger differences may indicate limited endurance or poor pacing in the 400. Smaller differences may suggest either very good endurance or underperformance in the 200 sprint.

WARM UP

• 10 minutes of mixed strokes.

PRE MAIN

• 6 to 8 x 50
• Build by each intervals to finish the last 50 strong

MAIN

• 400 Time Trial – Ensure you do the correct distance and pace yourself well. Having someone to time you will help.
• 5 mins rest.
• 2 x 25 –  #1 easy #2 moderate just to get yourself ready for the next TT interval.
• 200 Time Trial – Ensure you do the correct distance and pace yourself well.