About Critical Swimming Speed

Critical Swimming Speed (CSS) is your swimming velocity at about your maximal lactate steady state, expressed as yards or meters per second. Your CSS can be improved by training a little slower than your CSS (we call this Endurance Category 1, or EN1), just at your CSS (EN2), or a little faster than your CSS (EN3). Training Categories are described more, here: About Endurance Training Categories.

You can calculate CSS based on two maximal effort time trials: a short test of 200 yards and long test of 400 yards. Yards or meters, it doesn't matter what you use since we are measuring velocity. I use yards because most of the pools I use are measured in yards for most of the year. (Just don't calculate your velocity in yards and then apply that to a workout done in meters.) Perform these tests after a good warm-up and a couple of fast 100s (with rest), so that you are ready to swim fast. Swim both test sets starting in the water, pushing off from the wall -- no diving allowed. Swim the 400 first, and get fully recovered (say 3 minutes) before swimming the 200. These are maximum effort swims, but they should be done at a consistent pace - so if possible, have somebody record your split times. For each test, if your consecutive 100 split times vary by more than 5%, the test will not be valid. (If that happens, use your rating of perceived exertion, as described elsewhere, to set your training category paces.)

After performing both tests, use the following formula to determine your CSS:

(long distance - short distance)
------------------------------
(seconds to complete long test - seconds to complete short test)

For example, if your time for the 400-yard test is 6:35 and your time for the 200-yard test is 3:10, your CSS is .98 yards per second:

(400 - 200)        200
------------ = --------  =  .98 yards per second
(395 - 190)        205

You can then calculate your repeat times for each endurance training category based on your CSS, for all of the standard repeat distances. Or you can use a version of the calculator below. In theory you can use your CSS to predict race times for any distance, but there are other factors involved (weather, walls, crowding, etc.) and as Yogi Berra said, "It's tough to make predictions, especially about the future."

CSS Calculators

There are two versions of a CSS calculatrr. In addition to your CSS, the spreadsheet version displays your repeat times for each training category for common repeat distances. Note that these are swim times for each repeat, and you will need to add an appropriate rest time between repeats. You can access the calculators, below:

Excel Spreadsheet Version - Click to open the Excel spreadsheet file in your browser. If it will not do that, right-click and save the file on your system, and open in Excel or any other package that opens .xlsx (Microsoft Office 2010 Excel) files.
SwimSmooth Version - another webpage with good information and a calculator that is embedded on the page.

For a description of the endurance training categories, see About Endurance Training Categories.

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