Fat and Carb Burning

One interesting thing to look at in VO2max testing is how many grams of carbs and fat are oxidized vs heart rate. [Heart Rate is used as the surrogate for %VO2max]. My chart looks like:

The blue dots are fat oxidation. The brown dots are carbohydrate oxidation. Remember that carbs have 4 kcals per gram and fat has 9 kcals per gram.

Both curves are parabolas. The carbohydrate oxidation curve ends up being the limiting factor in exercise at high rare rates. My sweet spot is 120 bpm. My MAF number is 112-120 bpm. No coincidence there.

Normalizing the graph for calories is interesting since it shows the calories are somewhat comparable.

Here is Ben Greenfield’s data (in kcals also). It is quite similar to mine except Ben has more calories oxidized. Unfortunately I don’t have Ben’s heart rate data but VO2max is directly related to Heart Rate.

It is worth noting that Ben’s cross-over point is around 68% of his VO2max. Ben’s fat max oxidation is very close to my own rate (a little less actually).

Also, Ben barely goes to zero on his carb oxidation and it is at a very low 40% (approx) of his VO2max. Ben has said that his normal carbohydrate consumption was somewhere around 100 grams during the time preceding this test. Ben was relatively low carb for a high intensity athlete like himself.

Here is my data with the x-axis as %VO2max. Ben’s greater access to carb stores may help him.

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