Aerobic Swimming Speeds for Optimal Training

How fast should a swimmer go to get their desired training result?

Swimmer swimming in a pool
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When lifting weights, you have a pretty good idea how the work should be done. Up, down, a certain number of repeats with a certain amount of weight may be repeated in several sets. It may be based on a percent of the maximum you can lift or on a history of what you lifted previously. In the swimming pool, how do swimmers know how fast to swim to get the desired training result? This depends on the result they want to emphasize -- anaerobic or aerobic metabolism.

All swimming has some element of each, with aerobic work's contribution increasing as the distance being swum increases. Swimmers need to develop both of these areas -- pure anaerobic work is best done at the fastest possible speeds, so determining a pace is not quite so important to most swimmers -- just go as fast as you can! The distance swam and the amount of rest between swims helps to determine how fast you can swim each repeat; the work itself determines the speeds and what is being trained. There are many other factors, including the number of strokes taken per length or per second (distance per stroke or stroke rate) -- how much of each type of work to complete in a session, a week, or a training cycle -- and how to arrange workouts to get the most from what you are doing.

To target aerobic metabolism is not quite so easy. USA Swimming uses a generally accepted list of three different levels of aerobic work. Many other sports use a similar system to define work levels. Here, we'll use these definitions:

  • Minimum Endurance Pace (EN1) - almost any distance, with very low rest (less than: 30 seconds) between repeats, swum at a sustainable, fairly easy pace. This kind of work set takes 15 to 60 minutes (or more). It helps to build base yardage and promotes recovery. An example: 6 x 500 yards at EN1 pace with :15 seconds rest between repeats or 6 x 500 @ :15 rest, EN1 pace.
  • Threshold Endurance Pace (EN2) - usually distances less than 500 yards with up to: 60 seconds rest between repeats, swum at a pace faster than EN1 (we'll look at how much faster a little bit later). This type of set takes between 20 and 45 (or more) minutes to complete and should increase your ability to perform aerobic work without causing a build-up of waste products in the muscles, but should still be followed by a day of easy work to restore muscle glycogen stores. An example: 8 x 175 @ :20 rest, EN2 pace.
  • VO2Max Endurance Pace (EN3) - usually distances less than 300 yards with rest somewhere between :20 seconds up to a time equal to the amount of work completed (a 1:1 work to rest ratio) at a pace faster than both EN1 and EN2 (be patient - we'll get to it). You will probably not be able to hold this pace for much longer than 30 minutes. This kind of work can simulate the same overall effects of a race. It's very hard work and should also be followed by some type of recovery workout to restore muscle glycogen stores. An example: 8 x 100 @ :45 rest, EN3 pace.

It is important to balance your efforts to help prevent over-training. Do most of your work at these endurance levels, doing some of each type each week. A very rough rule of thumb for early season work is 50% EN1, 30% EN2, 10% EN3, with remaining 10% shared between very easy recovery paces (slower than EN1) and very fast anaerobic and power speeds. While all swimmers can benefit from some high-speed work, most do not need very much. You can develop speed by working at the endurance levels.

Remember, don't sacrifice technique for speed. You need to strike a balance; the fastest swimmers are usually those that hold the best technique at the fastest speed for the longest period of time. If you are just starting out it will be better for you to hold that good style as long as possible.

So, what should your pace be for EN1, EN2, or EN3 work? You'll need to establish some kind of base measurement or starting point.

How to Determine Your Threshold Swimming Pace

How do swimmers know how fast to swim to get the desired training result? All swimming has some element of anaerobic or aerobic metabolism, with aerobic work's contribution increasing as the distance being swum increases. There is a 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.
  • T-30 test (or its inverse twin, a timed swim over a set distance that takes about 30 minutes to complete).
  • 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.

For our purposes, we'll 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 (200s to 400s are recommended).
  • 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 do you use these aerobic swimming paces in a swim workout?

Examples of Aerobic Paces From a Modified T-30 Test Set

If you want to do a set to improve aerobic work levels without building up excess waste via threshold training paces (usually thought of as an EN2 set), you could do 18 x 100 @ 1:45, holding 1:23 per 100. This takes about 30 minutes and allows :20 seconds rest between repeats -- your job is to hold the pace for the entire set. Under most circumstances, you will be able to do this because you know it is a valid pace. Another example set could be 6 x 400 @ 6:00, holding 5:39 per 400.

What is the margin of error for holding a pace? As evidenced in the above table, a 3% difference in pace will move you up to the next level of work. You should be as accurate as possible in maintaining your goal pace for a given set. This will take some experience -- so don't be discouraged if at first, you are "all over the map" when it comes to repeat times. You will learn what each speed feels like; how to relate your perceived exertion to actual speed. As you improve your level of fitness and holding a goal pace becomes easier, it's time to repeat the test set to re-establish that goal pace.

Some days you won't be able to hold the "prescribed" pace. Why not? You might have been up too late the night before, skipped lunch, forgot to drink enough fluids, or still tired from yesterday's run. In these cases, you need to be good to your body and your brain -- if you can't do the work, change it! Do some easy swimming, focusing on your technique. Come back the next time fresh and ready to do the work. Rest is part of an overall workout plan. Without it, you can't perform the work at the correct speeds to get the results you deserve.

Try this method to plan your workout pace for different sets. If you keep track of how you are doing, you can make automatic adjustments and updates to your paces as you improve. Almost any EN2 set that takes about 30 minutes where you hold the fastest possible even pace can be used to update your paces.

Updated by Dr. John Mullen