CrossFit & The Energy Systems

Crossfit Energy Systems
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Firstly, let’s familiarise ourselves with the three main energy systems without trying to over complicate things, and then some really simple ways of how to train them. When I’m reading articles or trying to absorb information in lectures, I’m always looking for the easiest way to understand things. I always appreciate coaches or teachers that make it really simple to understand, and how they make it relevant to my sport (CrossFit). Hopefully this will be idiot proof…

The Aerobic System.

Think of the aerobic system as the big diesel bus with a massive fuel tank. While the aerobic system doesn’t produce nearly as much power as the other systems, a major feature is its capacity, which is virtually limitless, as it just keeps on producing ATP.

The aerobic system is not only the base for all other energy systems to build upon, but also for longer endurance work like long distance runs, or metcon’s lasting 15 minutes plus. A good example of a top athlete in our sport would be Sam Briggs. Think about her destroying ‘Murph’ at the CrossFit Games, tagging people’s hands as she cruised past them, whilst everyone else is thinking “How’s your capacity?”

If you are lacking in this energy system, work on building a solid aerobic base. This involves around 30min efforts, at a slow steady pace you can maintain a conversation at. Whether you choose running, bike riding or rowing, or a combination of the three, it is a good way to get you started. Then once you have that under your belt you can start to train in intervals at a slightly higher intensity – something like a 1km run, rest 2-3mins, repeat two more times. These would be at around 70% intensity.

The Lactate System.

Everyone reading this would have tasted what it feels like to experience the proverbial “Fran”, or heard the saying “Fran Lungs”. The lactate system is found in that 2-3 minute range when you’re left flat on the floor, feeling like you’ve been hit by a train. The lactate system is also hard to train as it puts so much stress on the body.

Spending too much time in the lactate systems is usually the mistake people make when starting CrossFit and sets them on the path to overtraining. Lactate training produces great results, but don’t over do it. Training this system is key when peaking for competitions and training it 1 or 2 times a week would be enough to see huge improvements.

Short end lactate power training should involve around 20-45s sprint type efforts with exercises that have high turnover rates, think rowing, burpees or KB swings, with enough rest to be able to hit it hard again. E.g. 5 moderate weight KB swings, 10 burpees going as fast as possible, then rest 3-4mins. Repeat a further 2-3 times.

Working into lactate endurance might look more like 250m row, 25 unbroken KB swings, 250m row, rest 7mins. Repeat 3 times.

The ATP-CP System.

We use this system in CrossFit when we do short-burst movements of intense energy, such as 1RM attempts, high percentage efforts of your 1RM, or short sprints. This system needs lots of time to recover, and too much volume can have a negative effect on your CNS (Central Nervous System).

Using general strength training structures such as 5×5 with 2-5mins rest is one way to increase strength, but there are other ways to help improve the energy system itself. Using “Every Minute on the Minute” (EMOM) scenarios with heavy weights is a great way to allow the system to recharge without running it into the floor. They are also useful routines for maintaining form while nearing fatigue, due to the lower rep ranges.

Try a 3 rep squat, 12 set EMOM. This allows you to lift significant weight for 36 reps (volume), but with enough rest inbetween to maintain form.


Hopefully these simple routines will help you train the different energy systems more efficiently, and support your development where fitness or capacity is currently hindering your performance down the box, or in the gym.

About the Author:

Kieran Baggs is one of the owners of CrossFit Civitas, our CrossFit partner, in West Wiltshire. You’ll find Kieran in the box lifting heavy stuff, and generally looking pretty badass in a Rambo-style headband.

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