Aerobic capacity, what is it and why it matters to you

Ryan ODonnellinstructionLeave a Comment

On Ben Bergeron’s blog he explains his programming philosophy, and introduces the concept of a “three-headed monster.” What is a “three-headed monster?” It’s someone that excels in all three of the basic focuses in Crossfit (strength, skills, conditioning). This is the guy or gal who can squat out of the gym, hammer out 15 unbroken muscle ups and then handstand walk home. He or she can also smoke everyone on a mile run or a 2k row. This last aspect is what we’re going to look at today.

So what in the world are we talking about here?

OK boys and girls, without getting too scientific there are a few things you need to understand to make the most of this blog post. Most importantly you need to know that our bodies have three energy pathways, they are: The ATP-PCr pathway, the glycolytic pathway and the oxidative pathway. The first two pathways do not require oxygen and are therefore considered ANAEROBIC while the third does require oxygen and is considered AEROBIC. The basic purpose of each one of these pathways is the same: to break carbon and hydrogen bonds in order to release energy and then use that energy to create more Adenosine triphosphate (ATP). Think of ATP as the fuel for your body, it’s required for all of life’s processes. That includes crushing weights (bro!), walking to the store, digesting food, picking your nose and wiping your…well, you get the picture. So how do these pathways work?



This is the first to kick into gear and it’s activated when energy demand is high (think heavy barbell lifts or short distance sprints). Although it works fast, it’s not long lasting. It’s typically active for up to about 10 seconds. The system is fueled by breaking phosphocreatine (PCr, Phosphate + creatine) bonds inside cells to release energy. This is why creatine supplementation can lead to increased muscular performance, more creatine = more phosphocreatine = NEW PR’s BRO! (In reality it takes more than that, but yes, it can help).


If you have a chemistry background, or are just moderately intelligent, you probably recognize from the name of this pathway that it involves glucose. This pathway works slower than the ATP-PCr pathway (from about 10-100 seconds), but can produce much more ATP. A good example of a Glycolytic exercise would be a 400 meter sprint or Josh Bridges’ Fran (Holy shit! This system is more complex than the ATP-PCr system, but the long and short of it is this: chemical bonds in bonds in glucose are broken to release energy. One more notable thing is this: hydrogen is a byproduct of the chemical reactions that take place in the Glycolytic pathway. It’s important because hydrogen ions cause muscle fatigue (burning). Lactic acid is produced in order to remove this hydrogen from our muscles and slow fatigue as a result. So, while many people consider lactic acid to be evil, it actually works to prevent muscle fatigue.

Oxidative system

The slowest moving pathway (used during exercise in duration of 2 minutes and above), but ultimately the most efficient is this last one. As you can see from the name, this pathway requires oxygen to function making it AEROBIC while the first two pathways are considered ANAEROBIC. It should come as no shock to you then that the reason you breathe harder during exercise is because your body needs to get more oxygen to create more ATP. This pathway is made up of two main parts one is the Kreb’s cycle and the other is the Electron Transport Chain (ETC). Like the glycolytic pathway, hydrogen is produced during Kreb’s cycle. However, as long as long as the rate of exercise is sustainable it will be pushed into the ETC and used to create mass amounts of ATP instead of fatiguing your muscles.


– ATP-PCr pathway: This pathway works for 0-10 seconds, doesn’t produce a lot of energy, used for short duration exercise (max lifts, short sprints).

– GLycolytic pathway: This works from around the 10 second mark to around the two minute mark. It uses glucose to produce energy and leads to muscle fatigue (burning). This system would be in use during a 400 meter sprint.

– Oxidative: This works during exercise lasting more than two minutes and also while you’re recovering between high intensity exercises. Unlike the above systems it requires oxygen making it AEROBIC, while the other two are ANAEROBIC.

Why does this matter to me?

When we talk about aerobic capacity we’re talking about how efficient our body is at using oxygen for energy. Some of you with a background in endurance sports may have heard about VO2 max, which is a measure of how much oxygen a particular person can use. Basically our aerobic performance in crossfit boils down to three things: how quickly do you get winded?, how often do you have to rest during WODs? and how long can you “push” for during WODs? If the answers to those questions are: “fast,” “a lot” and “not very long,” then you need to improve your aerobic capacity to be a more successful crossfitter. I’d like to draw your attention to this article on BOXROX ( which points out that a lot of world class athletes have been done in by an over-reliance on the glycolytic pathway and a lack of aerobic capacity over the last few years at the Crossfit Games. So you’re not alone, even the best of the best need to work on this.

So what can I do?

Let me start by saying this. There’s a reason people neglect conditioning work. IT F*CKING SUCKS. There’s a reason we see videos of people on social media hitting PR’s or getting their first muscle ups. Training that stuff is fun and afterwards it’s, “HELL YEAH BRO!” and high fives all around. Have you ever seen someone post an Instagram video of them hitting their PR timed mile? Of course not, because conditioning isn’t fun, it isn’t sexy and it hurts. There’s a good chance that if you come up and try to give me a high five immediately after I’ve just run a timed mile or done the “death by burpee 2k row” that I’ll scissor kick your head off. It’s miserable.

A strong base is key. The BOXROX article I linked above mentions that Jason Khalipa advocates spending part of the year working on long duration aerobic movements (60+ minutes of running, swimming, cycling, etc.) to build an aerobic base. Now, 60 minutes might seem like a long time for someone who isn’t trying to make the games, but hitting a 30 minute jog now and then is never a bad idea (active rest days, bro?). I know for sure my marathon training before I started crossfitting helped me immensely.

Intervals are also fantastic, they’ll help you push longer and recover faster (and burn fat, BEACH SEASON IS HERE!) Try this some time: on a rower 4x250m, 3x300m, 2x500m, 1x1000m, all intervals at your 2k PR pace, 30 seconds rest between each rep, 1 minute rest in between each set. HAVE FUN!

I will also point you to one of my favorite websites: Chris Hinshaw is the aerobic capacity guru in the Crossfit world and he’s helped a ton of big names in the business build their engines. He posts new workouts every Sunday night. I’ve been doing these for just over a year at least once a week, they work wonders.

Lastly, I want to stress that building a strong engine comes down to your mental capacity as well. Your brain will tell you to slow down or stop before your body has to. Often the only thing standing between you and those last 10 wall balls or sprinting that last 100 meters is that thing between your ears. Don’t listen to it.

If anyone is interested in more endurance type workouts or ways they can improve their AC don’t be afraid to reach out, you know where to find me. Thanks for reading.

– O’Dons

Bergeron, Ben. “CompetitorsWOD: Programming Philosophy.”CompetitorsWOD: Programming Philosophy. Competitor’s WOD, n.d. Web. 12 June 2016.
Bernardi, John, PhD, and Ryan Andrews, MS, MA, RD. The Essentials of Sport and Exercise Nutrition. N.p.: Precision Nutrition, 2016. Print.
Hamilton, Ross. “Crossfit Conditioning: Building a Powerful Aerobic Engine | BOXROX.” BOXROX. BOXROX, 06 Feb. 2016. Web. 12 June 2016.
Kennedy, Karen. “Training To Be A Three-Headed Monster.” CrossFit Insurrecto. CrossFit Insurrecto, n.d. Web. 12 June 2016.
Leyland, Anthony. “Energy Systems.” Madlab School of Fitness, n.d. Web. 12 June 2016.
“The Lost Art of Aerobic Training for Crossfit.” OPEX Fitness. OPEX Fitness, n.d. Web.

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