Is CrossFit a Carb Sport?

So I recently saw a statement online that stated that the sport of fitness (CrossFit as a sport and not the S&C protocol) was predominantly fueled by the macronutrient Carbohydrate. This statement immediately jumped out at me, for some reason I just couldn’t see it.

The argument: “CrossFit is a Carb Driven Sport”

The intensity of aerobic output that is carried out within the sport of fitness (CrossFit) will always be fueled by glycogen, with very little coming from fatty acids. The argument being that a lot of aerobic work requires huge amounts of muscular contractions through lots of different planes of motion and ranges of motion, and these contractions would appear to be fueled by the glycolytic and adenosine triphosphate and creatine phosphate energy pathways.

The Rebuttal:

In contrast to this I would suggest that, unless the weights are heavy enough and the WODs short enough to remain within the anaerobic pathway, it’s predominantly fueled by fats. Glycolysis will be used during the higher powered movements, but if the original statement were true and glycolysis was the main contributor, people would burn out very quickly. The thought process being that carbohydrates are metabolised at a faster rate. From my personal experience, I feel that during heavy weight lifting workouts, having a higher intake of Carbohydrates pre and during workouts leaves me with more energy, but during lower intensity aerobically charged workouts (think 5KM row 50 wall balls 5 KM Row), a lower level of carbs and higher fats leaves me feeling more energetic. It is safe to say that fats are the fuel source that support the use of carbs for energy. Just like the aerobic system supports the use of the other energy systems.

Aerobic is a very general term. If you do a 90 minute assault bike @75% then yeah a fair bit of fat utilisation takes place, but there will also be a high level of glycogen depletion. The energy systems are never black and white unfortunately.

If you’re doing higher aerobic threshold work like AMRAP 7min rest 2 mins x4

It’s highly highly glycolytic unless you’re going very slowly. To produce the power output required for CrossFit, fat oxidation is way too slow surely.

However true anaerobic glycolysis (assuming that we could utilise one energy system on its own, of which we cannot) only lasts for around 90secs to 2 min max, 42 min of work (AMRAP 7min rest 2 mins x4) would only ever become predominantly aerobic, there will be a high level of glycogen depletion due to the length of time that you are working for, but this doesn’t mean it would be the predominating source of energy, therefore, for longer duration work the body needs to be fat adapted and should utilise glycolysis only when it needs it. We would have to intake an inordinate amount of carbohydrates to fuel anything longer than 3 mins of true intense work. If that were the case most high level CrossFit athletes would be walking around with a higher level of body fat and look a little bit doughy. However the benefit of your athletic endeavours in the box will leave you more sensitive to insulin that is spiked by carb intake (not just carbs fats and protein also spike it just to a lower level) so this generally isn’t the case.

It is apparent though from my work with athletes of all levels within the competitive sport of fitness, they are often undersubscribed when it comes to carb intake in there diet, (let’s make it clear you need carbs within your diet). But increasing carb intake, and seeing an improvement in performance doesn’t always mean that glycolysis is the main contributor to energy production and subsequent force output during a classic 10-20 min workout.

It is important to remember that a strong association is not the proof of the causation.

An athlete should have the metabolic flexibility to predominate different fuel sources as an when required. It is not yet understood to which degree we can train this or whether we have the choice. A CrossFit athlete shouldn’t be trying to focus on one individual component as its impossible, without the aerobic system for instance we can’t reproduce energy in any of the other systems, I would suggest a lot of workouts especially at the CF Games are driven highly but not completely by fat metabolism, only once they move into the stadium are they favoring the higher levels of carbohydrate utilization and less fat oxidation due to the higher levels of force and power output required in single efforts, think 9/7/5 deadlift at 180kg and strict HSPU or a max clean and jerk or fran.  

Glycogen storage will deplete during longer workouts because it is metabolized quickly and depleted quickly, if it were the dominant source athletes would burn out just as quickly, as they would without enough glycogen. There is a lot of research out there that suggests carb intake during exercise especially endurance based events improves performance, however in the extreme it’s like taking speed during a long distance wod you will improve for a short period of time but eventually it will drop off and you have to take on more, the underlying fuel source surely is then, fat.

The glycogen storage (increased by carb intake) is there to allow you to push at a slightly higher rate and percentage of effort. It’s like getting a fire to burn a bit brighter and hotter, the hotter it burns the faster you have to refuel it. However it will continue to burn for a long time once you have stopped adding the accelerant to it.

It’s clear that no energy source or energy system is the working purely on its own at any one point, they work in tandem but the body does favour certain sources due to the nature of the work. There isn’t enough research to support any different and there most likely never will be because we do not have the technology to truly measure it and no matter what we do we need a balance of all 3 systems.

I presume that the general idea for that post was that in my experience a huge amount of athletes under fuel carbohydrates, this negatively affects training and performance for them. For the everyday athlete this will also negatively affect body composition. If there is a considerable drop in your work capacity during a long, short or mid range workout, you will ultimately not have the ability to work enough to reach your aesthetic goals.

We would be able to find a number of ‘experts’ to back up both sides of the argument. The human body is too complex to make general assumptions, every athlete is an individual and each has to take into account individual needs and differences. Some will do well on a ketogenic diet others will not. If you are looking to improve your body fat levels than a slightly lower carb intake may be useful on longer aerobic workouts. But during heavy lifting days a higher level will provide you the energy to lift more and improve your work capacity.

The main takeaway is find a coach that can work with you as an individual, take all things into account and experiment with your diet and constantly look to improve.

If you are unsure about any of the information in this blog please contact your Coach For Life for more information about how you can benefit from dialing in your nutrition.

Coach Lee

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