Perform this workout when you are well rested.

You should be able to swim 400 yards or meters at a fairly consistent pace before using this test. If possible, use a swim watch or have somebody else record your lap times, because if consecutive lap times vary by more than about 5%, the estimated CSS will not be valid (you need to swim at a more steady pace!) Also, if your pace during the 400 is faster than your pace during the 200, you were slacking off during the shorter swim!

Swim both time trials starting in the water, pushing off from the wall – no dives from the blocks or wall allowed.

Both time trials should be performed during a single workout, in lanes that are the same length. (In other words, if your pool is set up with both 25 and 50-yard lanes, use the same lane length for both time trials.)

It doesn’t matter if your pool is configured for meters or yards, nor does the lane length matter, although on these pages we talk about lengths as 25 or 50 yards or meters, since  those are the most common lane lengths. You just need to perform a “long” swim (about 400 yards or meters) and a “short” swim (about 200 yards or meters).  Any two distances in that range will do: one about half the distance of the other, with the shorter distance taking about two minutes or more to complete, because the calculation estimates your threshold pace based on the speed difference between the longer and shorter distances. Traditionally, the distances used are 400 and 200, so we use those distances here.

Warm Up

400 FS +30s rest

Swim a 400 warm up, followed by (at least) 30 seconds of rest.

Pre-test Speed Set

2 X 100 FS +1:30 rest

Swim two quick 100s; not all-out sprints, just fast 100s, with at least 90 seconds of rest following each, so that you’re ready to swim fast for the time trials.

Long Time Trial

400 FS +5:00 rest

Swim the fastest even pace that you can maintain for the entire distance. Then rest for 5 minutes or more, optionally swimming an easy lap or two. Be sure you are fully recovered before performing the following shorter time trial.

Short Time Trial

200 FS +2:00 rest

Swim the fastest even pace that you can maintain for the entire distance.

Calculate Your CSS (or threshold velocity)

Enter your long and short time-trial times in a CSS Calculator, or calculate your CSS manually as follows:

(long distance – short distance) / (long seconds – short seconds)

For example, in a 25-yard pool, if your 400 time is 5:48 and your 200 time is 2:45:

(400 - 200)        200
------------  =  --------  =  1.09
(348 - 165)        183

Your CSS is 1.09 yards per second.

Use this velocity to calculate your threshold-speed length time (TL) – the time it takes to swim at CSS for one length of the pool – by dividing the lane length by your CSS. Continuing the example above, the time it takes to swim 25 yards at threshold pace is:

 25 (yards)
----        =   22.88 seconds per 25-yard length
1.09 (CSS)

TL = 22.88 seconds

With your TL, you’re ready to perform CSS based threshold workouts.

If you own a Tempo Trainer Pro, or some other device that you can set to beep at a fixed interval, you can set it to beep at the end of every length, and then strive to arrive at the wall exactly on the beep. The first few “walls” should be easy, but resist the temptation to go faster; it will get harder soon. But note that if it doesn’t get harder after about 400 yards or meters, your CSS needs to be adjusted, which you can do by re-taking the test, or by just setting your TL down by a second (or some fraction of a second).

Continuing the example above, you would set the Tempo Trainer Pro to beep at every wall by selecting Mode 1 and entering 22.88 in the display. Then, during your threshold sets, hit the top button to restart the timer at the start of each interval, and strive to hit a wall on every beep!