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Training Energy Systems for the Swim

By Dave Burgess | Feb. 21, 2019, 1:16 p.m. (ET)

Swim Energy Systems

Far too often I see triathletes training in the pool doing the same workout: Long swims at a moderate aerobic effort. The old-school thought behind this is that endurance is the primary necessity for the swim leg of a triathlon. The other old-school thought is that you can’t win a triathlon in the swim and that you just need to get through that leg.

Both of those philosophies are antiquated and incorrect.

The best example I give athletes is the analogy that they do power/VO2 workouts on the bike, and they go to the track to do speedwork for their run. Why aren’t they doing the same type of workouts for their swim? To be a well-rounded triathlete, you need to work the aerobic, anaerobic, and VO2 systems in the pool just as you do with the other disciplines.

Assuming that form and mechanics are solid (because without good form fast swimming can’t occur), you’re then ready to focus on your energy systems for maximum effect.

So let’s move on to properly understanding how to work the varying energy systems in the pool. You first need to understand what you are capable of in regards to pace and effort. Understanding your base 100 time allows you to tailor a workout with the proper sendoffs to work the energy systems appropriately. We’ll cover how to determine the base 100 time of an athlete and how to apply that information shortly.

Another old-school training methodology that I see is a swim set written with a static amount of rest. For example:

10 x 100 @ 20 seconds rest.

The issue here is that it doesn’t matter how long it takes you to swim each 100-meter effort, or whether you begin to fatigue and slow down. You will always get 20 seconds rest regardless of effort and pace, and subsequently the goal energy system may not indeed be engaged as planned.

By knowing what your base 100 time is, sets can be designed specifically for the you, and proper sendoffs applied to ensure the effort and rest is tailored to the energy system being worked that day. So, how do we get that information? A simple swim set will help determine this metric. This test set (or some variance of it) is utilized by many USA Triathlon coaches across the country.

Begin with a good warmup and a warmup set or two. Then the test set is as follows:

1 x 100 at approximately 95% effort

90 seconds rest

1 x 500 for time.

Now, the 500-meter (or yard) effort can be shortened to 400 meters depending on your current ability and endurance levels. And as a bit of instruction regarding that set: While it’s a hard effort you must remember that it’s a 500. You can’t go out as fast as you did in the first 100-meter effort. A hard, well-paced effort is what is required.

With that 500-meter time in hand, you can then determine the average 100-meter time that you can most likely hold. For example, if your 500-meter time was 7:30, we know that your "average" 100-meter time is approximately 1:30. With this data, any workout can be written to work the appropriate energy system. Going back to our 10 x 100 set above. If we wanted to ensure that you get :15-:20 seconds of rest on each 100 (ensuring a good aerobic effort throughout the set), then the set can be written thusly:

10 x 100 @ 1:50

Meaning that every 1:50 you are pushing off for your next 100-meter effort. You have to work for that rest. If you slow down, you get less. If you maintain pace, you get what is required to work the energy system in question. Yes, effort will go up over the duration of the set, and that’s OK. Structuring sets in this fashion pays massive dividends.

So how do we create workouts for the aerobic, anaerobic, and VO2 energy systems? It’s all about the work-rest ratio. Or, more simply, the effort exerted and the amount of rest the athlete gets.


Aerobic efforts/sets yield approximately :15-:20 rest on a steady state effort (depending on the individual). Lactic acid is buffered fairly easily by the body during these efforts and rest intervals. These types of workouts focus on straightforward endurance.

Anaerobic efforts/sets yield :10-:15 rest on a harder effort (again, depending on the individual). Lactic acid cannot be buffered as effectively here. These workouts assist with speed endurance.

VO2 efforts/sets yield almost a full recovery between a shorter, maximal effort.


Aerobic sets can look like the following simple workout:

10 x 200 @ 3:30 (a base 100 time of 1:30 plus :30 rest)

Longer efforts can, and should, be included in programming (800’s, 1000’s, etc.). At that point, static rest (1:00 minute or so) between efforts will be just fine.

Anaerobic sets can then look like the below set of increasing effort and intensity. While it starts aerobically, with less rest being provided as one progresses through the set, effort levels go up, lactic acid begins to build up (and is not buffered as efficiently), and the anaerobic engine begins to be worked more effectively.

6 x 100 @ 1:50

6 x 100 @ 1:45

6 x 100 @ 1:40

VO2 sets that work on pure speed (as stated, just like going to the track to work on running speed) are short efforts at maximal output, with almost full recovery.

6 rounds

1 x 25 @ 1:00 max effort

1 x 50 @ 2:00 max effort

1 x 25 @ 2:00 easy effort

Please note that these are just examples of various “main sets." Once you know your base 100 time, you can write most any set to work the necessary energy systems creatively and effectively. And again, these are just examples of simple sets. If you’re not comfortable writing swimming workouts, that’s OK. Do some research—or contact a USA Triathlon certified coach.

It is critical that all energy systems be addressed in your swim training and programming. Not only will it make you a faster swimmer, but it will make you a more well-rounded and competitive triathlete.

Dave Burgess is a USA Triathlon Level II Certified Coach, USA Swimming and ASCA Level 3 Coach, and has been involved in the triathlon and endurance sports community since 2000. Dave is also  a US Masters Swimming Level 3 coach.and he holds a certificate in sports and performance nutrition. As the founder and head coach of Podium Training Systems, Dave works with athletes of all levels, from first-time competitors to elite-level athletes, competing in all race distances. Learn more at

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.