045 Metabolism in CrossFit

The Paul Weber Podcast

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Metabolism in CrossFit

1. Energy Contribution

3 pathways

To what extent are each of the three energy pathways active?

Intensity and duration dictate energy contribution from the three pathways.

CrossFit is often supramaximal in intensity:
-the task is only sustainable for a brief period
-the task requires anaerobic metabolism

Duration is tricky – because it’s constant work:rest scenarios – “12 minutes” is a misnomer – even a single wall ball is it’s own work:rest scenario

Isabel was 45% glycolytic, 40% oxidative, 15% phosphagen.

Some direct studies found that metabolism in CrossFit is similar to repeated Wingates.

Aerobic energy production is activated during very intense exercise, and 70–100% of the VO2 max can be reached in a Wingate.

~50% of the energy contribution in the last 5s of a Wingate is aerobic.
2. Fuel Substrates

3 major substrates

Once you transition from ATP-PC pathway, fuel substrates are getting utilized.

The major substrates are:
muscle glycogen
blood glucose (derived from the liver and from the gut when carbs are ingested)
fatty acids (derived from both muscle intramuscular triglyceride and adipose tissue)

Similar to the relative contribution of each metabolic pathway, intensity and duration determine the relative contribution of each fuel substrate.

Even during marathon and triathlon events lasting 2–2.5 h, there is a primary reliance on carbohydrate oxidation.
So what?

Even at maximal intensity, aerobic energy production is significant even in short durations.

The relative contribution of the aerobic and anaerobic energy systems is similar.

Ideal CrossFit training should include the development of both aerobic and anaerobic energy systems.

Anaerobic training is, by definition, intense. If it is not intense, it is not anaerobic.

Intense training is volume-limiting. It prevents you from training extensively.

Anaerobic training induces a greater stress-response, and is more likely to induce overtraining leading to burnout. For both physiological and psychological reasons.

Be sustainable. Sustainable intensity intra-workout, we suspect, is a proxy for sustainable intensity intra-microcycle.

Training sustainably cycle to cycle is necessary to accumulate the volume of training necessary to reach individual potential.

https://www.nature.com/articles/s42255-020-0251-4

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