EPOC, what is it and how does it affect weight loss?
The main concept here revolves around creating an oxygen debt during exercise, that later needs to be repaid. Let's start by explaining how the debt is created in the first place and to understand that I'll briefly explain our body processes energy.
Energy Transfer Systems
When you start running the first system that kicks in is the ATP/PCr system. This system uses the energy in the bonds between Creatine and Phosphate in our cells. This system will provide roughly 10 seconds of energy.
After that, your body switches over to the Glycolytic System. This system uses glycogen stores in your muscle tissue and breaks that glycogen down into glucose. That glucose is then used to regenerate ATP (our cells energy source). This system has some byproducts, pyruvate and NADH. We eventually hit what is called the anaerobic threshold (AT), because ATP generation can't keep pace with energy expended, and we need to switch to the next system which requires oxygen. A person will usually be able to exercise intensely for about 80-90 seconds before this threshold is hit. You'll notice this when you are running when you have to make a more drastic slow down in your pace and you notice a little burning in your legs.
Oxidative Phosphorylative System
Once you hit that threshold your body then kicks into the third system the Oxidative Phosphorylative System. This system needs oxygen in order to function, hence oxidative in the title that means with oxygen. This system is the real powerhouse in energy transformation and supplies our cells with a bulk of the energy they need after that initial 90 seconds or so. Activities that do most of the work in this system would be considered aerobic activities because they are done WITH oxygen.
Repaying your Debt
This is where EPOC comes into play. After you are done working out your body needs additional oxygen to do 3 main tasks:*
- Metabolize additional nutrients
- Replenish the energy stores that have been used up
- Reload the depleted oxygen stores in the muscle and blood
Therefore, exercise intensity directly relates to longer excess post-exercise oxygen consumption (EPOC). This is why we recommend the workouts that we do versus straight cardio or traditional weight lifting with longer breaks between sets. It is because of this that higher intensity workouts that involve some strength training is the best solution for fat loss. If your goal is something else, than there are other options out there.
Just one specific example of how EPOC works, in one study an individual that did circuit weight training (bench, power clean, and squats), 10 reps, 4 sets of each and completed all of that in 31 minutes, had an elevated EPOC for the next 38 HOURS!!!! They actually stopped measuring at 38 hours so it actually could have been longer. This is where the magic happens when it comes to boosting metabolisms and fat loss. It's not what happens during the workout that really matters its what our bodies do to recover from that workout that really affects body composition.
I'll end with a quote from Alan Aragon: