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The Power of EPOC & Metabolic Pathways

Last week’s blog post we discussed metabolism and several ways to make our metabolism work more efficiently with actions that anyone can take to improve overall calories being burned through out the day. This week let us stay in the same direction and talk about what exactly is our energy sources that we use and how “E.P.O.C”; Excess post exercise oxygen consumption work.

Where does our energy come from within the body and how does our bodies convert food to energy?

Our bodies need a constant supply of energy to maintain the bodies natural level of homeostasis, (internal balance). When exercise places stress on the body, this places a unique demand on the body ability to supply energy and remove metabolic by- products that is produced during exercise.

We eat food to replace the energy used through out the day to survive and function. Before using this energy source our body must break down substrates (Fats, Protein, Carbohydrates) down to its smallest form These are converted to substrate molecules that are chemically released into our cells and stored for later.

This energy is known as adenosine triphosphate” or “A.T.P.”, when the chemical bonds that hold ATP together are broken, energy I released for your cells to do work, for example muscle contraction when doing a bicep curl. Once ATP is broken down what is left behind is another molecule called adenosine diphosphate or “A.D.P”. Once all the free energy is replenished our cells reattach the phosphate group to ADP and restores ATP levels back to normal.

We recycle our own energy and convert this ADP back to ATP to be used to perform more work. We need energy to convert; that is why we need make sure we are eating when we need too, getting enough sleep to have our hormones properly function to signal to body when energy is released and when we need to consume more to restore the energy, getting enough protein with each meal as well with help keep you fuller longer to assist with maintaining a balance in the body.

If our hormones are not balanced, our energy output is not balanced, we will be tired, less efficient, and consume more calories per meal due to a higher heart rate and insulin levels during sleep. Resulting in an overall consumption of more calories. Metabolism is referred to the chemical reaction that we spoke if earlier when broken down into its smallest form to be used as energy, now that we understand how energy is converted into the smallest form, let us dive right into EPOC.

Oxygen debt or “EPOC”, is the amount of oxygen required to restore the body back to its normal resting level. Just as a vehicle is at rest after use, the engine is still warm for a period until is slowly cooled; this would be the same if applied to the human body. We produce a higher amount oxygen after a workout, our body must work keeping our metabolism at a higher rate until the body returns to homeostasis.

Our bodies enter several metabolic pathways when generating ATP (our energy supply); The ATP-PC system, The Glycolytic system, and The Oxidative system. Our body will start in these three metabolic pathways as soon as you start moving and warming up.

The first system ATP-PC stored energy is used up instantly within 15- 20 seconds recovery for this system takes up to 90 seconds. This would be an equivalent if you do a sprint, but small portion of the ATP-CP is still anaerobic & aerobic metabolism. When exercise and movement is increasing our body switches over to another energy system up to 2 minutes; The Glycolytic system; this system takes several minutes, to convert into the final pathway the oxidative system where this becomes the final system would be used into long steady jogs or bike rides, this is where oxidation of glucose (sugar) and fat (lipids) are the primary energy source.

Our fat storage is unlimited, but all the other energy source are not, that is why it is a good recommendation to only exercised up to 90 minutes if you are a beginner or intermediate; to help with restoration of muscle glycogen.

Our energy will be slow as the primary energy supply turns to fat. That is why its smart to always have a carbohydrate replacement if you training sessions go longer than 90 minutes; most athletes will train for a longer period. Proper supplementation is suggested if you are training for more athletic purposes. Having electrolyte drink or Branch chain amino acid to help replenish the carbohydrates and amino acids during the training session.

How do we achieve this and apply this to our training?

A few specific types of training modalities will influence EPOC. Performing strength training or any form of resistance training is paired with circuit training and small rest periods will have a big effect of EPOC. Keeping all the movements multi-joint, switching from upper body to lower body during exercises will involve more muscle contractions. Heavier training loads and shorter recovery intervals increases the demand on the anaerobic pathways during exercise, which will have a greater EPOC effect during post exercise recovery.

EPOC is also influenced by the intensity of a workout not so much the time duration. Higher intensity will dip into the anaerobic pathways. When EPOC occurs, the body uses oxygen to restore muscle glycogen and rebuild muscle protein damage during physical activity.

HIIT training is considered the best way to get the most stimulation from EPOC, even when your work out is over the body continues to use aerobic energy pathway to replace ATP consumed during your work out, creating a greater EPOC effect. The intervals of work and rest allow the body to replenish the ATP that was used, that is why HIIT training is considered the best way to influence EPOC.

Overall to get the best EPOC for your buck; perform heavy weight training or HIIT training with shorter rest periods, or high intensity intervals with cardio will be well worth the work. I hope this blog has given you a better understanding on how our energy systems interact with body and what we can do during our training sessions and after to help perform better every time we step into the gym!


1. C.A Micheal. DPT, MS ,CES, PES. et al (2018) NASM Essential of Personal Fitness Training. Jone & Barllett Learning.

2. P. MCcall . MS, CSCS.(2014) " 7 Things to Know About Access Post- Exercise Oxygen Consumption". Article from American Counsel of Exercise.

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