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 - you just go as fast as you can! The distance swum 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 will 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 take 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 affects 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.