Where does fat go?

Fat loss if one of the main reason people exercise, but how many people know how the process of fat loss happens. The video below explains how it occurs.

So after fat is broken down, we ultimately breathe it out. This explains, why high intensity exercise – HITT, Crossfit etc have been shown to more beneficial to fat loss than steady state exercise – jogging. This can be explained by excess post-exercise oxygen consumption (EPOC) or oxygen debt.

Our bodies have two energy systems

aerobic system, uses oxygen to generate the energy molecule ATP.

anaerobic system, doesn’t use oxygen to generate ATP.

The intensity of the exercise decides which energy system is used. The anaerobic system generates ATP for high intensity exercise (HTT, Crossfit, etc)  while the aerobic system generates ATP for low intensity exercise (jogging). The aerobic system is more efficient at generating ATP.

During the recovery period after exercise, oxygen is used

⦁ to produce ATP and to replenish the ATP stores, that were used when exercising.

⦁ to restore oxygen levels in the blood.

⦁ to repair damaged muscles.


The oxygen debt is the difference between the volume of oxygen consumed to meet the energy demands during exercise ( anaerobic + aerobic systems) compared to the volume of oxygen consumed if the energy demands were met only by the aerobic system.


Therefore high intensity exercise creates a large oxygen debt. A large oxygen debt, requires a increased volume of oxygen consumption post exercise. It has been measured that to consume 1L of oxygen, 5 calories are burned.  So an increased volume of oxygen consumption means an increased number of calories burned.

In theory the more intense we exercise, the higher and longer the EPOC, which leads to an increase in calories burned and therefore lead to an increase in fat loss.

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