Understanding Fat Oxidation in Endurance Sports I
A very misunderstood topic is fat oxidation. Either it's “keto/fasting/low carb", "trust me bro" advice out there, or a misinterpretation of the role of fat burning in performance with endurance sport. This article is going to explain the basics of fat oxidation. The hope is to provide broader brush strokes around the nuances of fat oxidation, and the definitions of the concepts in the field at the moment, and empower the athlete to new performance levels.
Let's answer the following questions:
Where does Fat Oxidation take place in the muscle cell?
What is the CrossOver Point in fat metabolism?
What are Peak Fat Oxidation and FatMax?
Practical Steps to Calculate Peak Fat Oxidation outside a laboratory setting.

Where does fat oxidation take place in the muscle cell?
Fat is primarily stored in adipose tissue and once acted upon by certain hormone signals, is liberated into free fatty acids and glycerol. In Fig 1 below, the free fatty acid pathway is to be activated into (fatty) acyl-CoA (yes that's the correct spelling) where through a process called Beta Oxidation, the important intermediary called Acetyl- CoA is formed that can then enter the Krebs Cycle (see Fig 2). Acetyl CoA fuels the Krebs cycle and allows the production of ATP (the body's energy currency) via the Electron Transport Chain.


Now that we understand energy metabolism to a greater extent, let's move to understand key specific terminology
Crossover Point in Fat Metabolism
Originally a phrase coined by Brooks and Mercier, the Crossover point is a model that shows how the body increasingly shifts from primarily fat metabolism at low