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How to Determine Your Threshold Swimming Pace


In the swimming pool, how do swimmers know how fast to swim to get the desired training result? This depends on what result you want emphasized - anaerobic or aerobic metabolism. All swimming has some element of each, with aerobic work's contribution increasing as the distance being swum increases. What kind of swim test can you do to find your aerobic swimming paces?

First, we'll determine your threshold (EN2) pace. Several different methods are available to determine this starting point. Among them are:

  • Adjustments to pace based on the results of ten x 100 yard (or meter) swims on very low rest, also called a cruise test.
  • Perceived level of exertion (you may be familiar with the Borg Scale).
  • Heart rate levels.
  • Direct measurement of blood lactate levels.
  • A T-30 test (or its inverse twin, a timed swim over a set distance that takes about 30 minutes to complete).
  • A modified T-30 test. Other time trials, such as 1,000 meters or yards at the fastest possible pace, then dividing by 10 to derive an estimate of EN2 pace per 100.

Each has its good and bad points, heroes and detractors. Work paces are relative to you and your current level of conditioning; they will change as you get in better shape, so you have to re-measure your pace on a regular basis, perhaps as often as every two to three weeks.

We are going to use the modified T-30 test, primarily for its versatility. It can be done many different ways, it can be used for different strokes, and it can fit it into a regular workout quite easily. The modified T-30 test:

  • Takes about 30 minutes to complete.
  • Includes repeats of almost any distance (I recommend 200s to 400s).
  • Includes short rests between repeats (:10 to :20 seconds).
  • Is performed at the fastest possible average speed or pace (it might take you two or three attempts to gauge this fastest possible sustainable even pace).

If you know that you can do 300 yard repeats and hold a speed of 4:30 for each, you might do a modified T-30 test set like this: 8 x 300 @ :10 rest, with a 4:30/300 pace or faster (but if you do hold a faster pace, you must hold that same speed for all 8!). Another way to describe this set would be 8 x 300 on 4:40, holding the fastest possible pace for the set (you would start a new repeat every 4:40; your rest would be the difference between the time swum and the start of the next repeat).

You could do longer or shorter repeats, or even a straight 30 minute swim (a real T-30). The important variables are the duration of about 30 minutes and the fastest sustainable even pace for that time. Your actual sustained pace, or speed, is equal to your threshold (EN2) pace. This is your goal pace to hold for EN2 type sets.

If you held 4:15s for the above set of 300s, then your EN2 pace for a 100 is...

4:15/3 = 1:25/1
1:25 per 100
Convert everything to seconds, do the math, then convert back to minutes and seconds:

  • 4 minutes :15 seconds = 255 seconds per 300
  • 255 divided by 3 (one hundreds) = 85 seconds per 100
  • 85 seconds per 100 = 1 minute :25 seconds per 100
  • Note: You must also make a slight adjustment for distances of 100 yards or less, subtracting about :02 seconds per 100 - this makes your adjusted pace per 100 1:23 for distances of 100 or less, and 1:25 for distances greater than 100s.
  • VO2Max (EN3) pace is usually :01 to :03 seconds faster than your threshold (EN2) pace.

Based on the above example test, the paces are:

  • EN2 pace for 100s and shorter repeats = 1:23/100 or :20.7 seconds/25
  • EN2 pace for distances greater than 100s = 1:25/100 or :21.2 seconds/25
  • EN3 pace 100s and shorter repeats = 1:20 or :20 seconds/25
  • EN3 pace for distances greater than 100s = 1:22/100 or :20.5 seconds/25.

Looking at this pace per 100 for different distances results in:

  • Distance of Repeat = 25, EN2 Goal Time = 0:20, EN3 Goal Time = 0:20

  • Distance of Repeat = 50, EN2 Goal Time = 0:41, EN3 Goal Time = 0:40

  • Distance of Repeat = 75, EN2 Goal Time = 1:02, EN3 Goal Time = 1:00

  • Distance of Repeat = 100, EN2 Goal Time = 1:23, EN3 Goal Time = 1:20

  • Distance of Repeat = 125, EN2 Goal Time = 1:46, EN3 Goal Time = 1:42

  • Distance of Repeat = 150, EN2 Goal Time = 2:07, EN3 Goal Time = 2:03

  • Distance of Repeat = 175, EN2 Goal Time = 2:28, EN3 Goal Time = 2:23

  • Distance of Repeat = 200, EN2 Goal Time = 2:49, EN3 Goal Time = 2:44

  • Distance of Repeat = 300, EN2 Goal Time = 4:14, EN3 Goal Time = 4:06

  • Distance of Repeat = 400, EN2 Goal Time = 5:39, EN3 Goal Time = 5:28

  • Distance of Repeat = 500, EN2 Goal Time = 7:05, EN3 Goal Time = 6:50

So now... how do I use these aerobic swimming paces in a swim workout?

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