What is EPOC?
EPOC stands for Excess Post Workout Oxygen Consumption. But what does this really mean?
To answer this question, we need to take a step back. Let’s first clarify how our body fuels its biological processes,
without delving too deeply into physiology, so these concepts remain accessible to everyone.
Energy Systems
Our body constantly needs energy, both to keep us alive and to carry out all our daily activities. Hence, it must never run out of energy, and it primarily relies on a molecule called ATP (adenosine triphosphate).
ATP is the foundation of all our energy metabolism, like saying an atom is the fundamental unit of matter.
Why is ATP so important? ATP is crucial because it serves as a readily available energy store for our body.
By breaking certain chemical bonds in this molecule, our body can extract the energy required to perform various chemical reactions,
whether for muscle contraction or other processes.
To always have ATP reserves ready, our body has three main energy systems: anaerobic alactic, anaerobic lactic, and aerobic. These three systems, which we will briefly examine, differ in many ways, but the main difference lies in the speed with
which they synthesize ATP molecules.
Anaerobic Alactic System
This is the fastest energy system. It provides energy almost instantaneously, but ATP reserves deplete quickly. This system is predominantly used by sprinters, for example, who run at maximum speed for about 10 seconds.
It is estimated that the anaerobic alactic system can produce energy for no more than 10-12 seconds.
ATP production here occurs without oxygen, through a reaction involving two molecules: ADP (adenosine diphosphate, a precursor of ATP) and phosphocreatine.
Anaerobic Lactic System
To simplify, this energy system offers intermediate characteristics between the anaerobic alactic and aerobic systems.
It is primarily involved in physical activities lasting up to 120 seconds. It uses glucose as an energy source to produce ATP, and one of the by-products of these chemical processes is lactate.
Lactate is the substance that makes us feel fatigue. When we run too hard, for instance, our legs may feel heavy,
losing their ability to contract effectively. This happens because the muscle fibers in our legs become saturated with lactate, preventing normal contraction.
Aerobic System
This is the last energy system and also the slowest. It provides a limited amount of energy, but theoretically, it can do so indefinitely, as long as there are glucose, proteins, or lipids to burn.
The aerobic system is used by marathon runners, for instance, and, as the name suggests, it operates in the presence of oxygen.
It kicks in after 120 seconds of activity and can be seen as a continuation of the anaerobic lactic system. It’s also the energy system that our body uses when at rest.
Without physical exertion, our body prefers to use lipids for energy, leveraging this system.
EPOC
Now we can finally discuss EPOC. The three energy systems described above actually work simultaneously during physical exertion.
Of course, the contribution of each system varies depending on the type of effort made. However, it is always the aerobic system that takes on the task of replenishing the anaerobic energy systems.
– For the anaerobic alactic system: The aerobic system restores baseline levels of ATP and phosphocreatine used.
– For the anaerobic lactic system: The aerobic system helps eliminate the lactate produced.
This is where the concept of “oxygen debt” comes into play. The more significant the exertion and the involvement of the first two energy systems during physical activity, the greater the amount of oxygen needed to restore baseline levels of the anaerobic systems.
This results in the so-called oxygen debt, which the aerobic system must address.
Conclusions
Why does EPOC matter? EPOC is crucial because it is the key to weight loss.
After all the discussion above, it is clear that the greater the effort during a workout, the more the anaerobic energy systems are activated.
This leads to a higher oxygen debt that the aerobic system must compensate for by burning fat!
Yes, you read that correctly: fat is burned at rest after intense exercise.
Getting up early for a morning walk to lose weight is futile. This way, you only burn fat during the walk itself. However, since walking is a low-intensity effort, very little fat will be burned.
To truly become a fat-burning machine, you need to push your body beyond the baseline levels of the anaerobic energy systems, increasing EPOC.
This, in turn, forces the aerobic system to burn fat as the body rests after completing the workout. Just think about it: studies have shown that a well-done workout can result in EPOC lasting up to 12 hours.
So, hypothetically, you could burn fat for 12 consecutive hours after the workout. Not bad, right?