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Energy Systems

Hey Vic City,

In CrossFit not only do we vary the movements that we perform in our WODs, but we also vary the duration of those WODs. Our body's effective use of energy systems will supply the demand for whatever the workout, or world throws at us. There are three energy systems that we use and I'll explain the main differences between them. All these systems overlap, and are being used simultaneously but at certain intensities some will be predominate.

Energy system 1 - The anaerobic - Phosphocreatine (PCr) System. This system uses Adenosine Triphosphate (ATP) that is stored in muscle cells. This reaction happens in the absence of oxygen and provides a lot of energy quick! The down side it only lasts for max efforts (~10 seconds). Ex. 100m Sprinter/Olympic Weightlifter

Energy system 2 - The anaerobic - Lactic Acid System (LA). This system breaks down glucose molecule for energy. It produces lactic acid as a by product (which can leave you feeling the burning in your legs, especially during Assault Bike). This system lasts from 30 seconds to 3 minutes, depending on intensity and fitness level. Ex. 800m Runner/Benchmark WOD Fran

Energy system 3 - The Oxidative (Aerobic) System. This system use oxygen to fuel the breakdown of nutrition for energy. This system is essentially infinite as long as you are getting oxygen and have food to turn to energy. During exercise lasting longer than 90 minutes, carbohydrate replenishment is recommended. Furthermore, the aerobic system aids in the removal of lactic acid which helps you tolerate more during your short bursts. Ex. 10km Runner/Hero WOD Murph

What does this mean for you?

Training and working to improve all these systems will increase overall fitness. This is also a good place to look to notice weaknesses in fitness, not just general movements, but time domains. Intervals are a great way to build these systems, often we are working 3 minutes or less then some recovery before repeating. Then the total duration of the workout will give the aerobic system a good stress, hitting two energy systems. There are many CrossFit WODs in a tough time domain, 7-20 minutes. This will test the development of your Lactic Acid System as well as the power of your aerobic system.

Knowing what our systems are capable of, and knowing we can't go 100% for 10 minutes straight, maybe try to slow down the first part of the WOD and save some energy for the last 1-3 minutes.

Check out this video of Matthew Bickel hitting 75 cals in 60 seconds on the Assault Bike. This is a pretty good use of the anaerobic system. You can see how fast he started and was able to maintain max for what looks like 10-15 seconds then starts to slow down a bit. At about 25 seconds in, he looks at the clock, indicating to me his muscles are starting to run out of energy and the 'burn' is setting in. By the last 20 seconds he was still moving but much slower than that initial pace. All of this happened in 60 seconds.

Just like movements you aren't good at, don't neglect energy systems that you aren't good at. Train your weaknesses and make them strengths.




WARM UP: Rowling - 3 x 120m

SKILL: Turkish Get Ups - 10-15 min of practice, go slow and focus on solid positions


This workout keeps the intro to this season of running going and mixes it up with a classic high output exercise, the power clean to overhead. Choose a weight that allows you to cycle quickly (although not necessarily unbroken!) through the rounds.

Warm up prior with at least 1 x 300m to get your legs ready to run.

Rx: 400m run, 21 clean and overhead (65/95), 400m run, 15 clean and overhead, 400m run, 9 clean and overhead, 400m run

FG2: 55/75

FG1: Scale bar weight as needed, run 200-300m for each run

TG: Scale as needed

CP: do the workout faster

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