What is Post-Exercise Oxygen Consumption?
Let me start by talking about what excess post-exercise oxygen consumption (or EPOC) actually is. Sometimes excess post-exercise oxygen consumption is called the “afterburn effect.”
Believe it or not, this concept is not new… it goes back to the early 1900s!
Back in 1910, researchers actually had the technology to measure how many calories a person was burning. In case you want to nerd out on this, I’ll tell you what this machine is called: a calorimeter. Personally, I didn’t even know this technology existed back then!
Anyhoo, back then, researchers suspected that there was something going on. After someone exercised, their bodies had to return back to normal and doing that probably took some energy.
It turns out their suspicions were correct. But even to this day, we don’t truly know what’s going on.
What Causes Excess Post-Exercise Oxygen Consumption?
Here’s the theory according to most researchers: after we exercise, the body does indeed have to adapt and try to return to pre-exercise levels. For example, after we cool down, the body has to replace the oxygen that was used in the blood and muscles. This is where the “oxygen consumption” comes from in the term “excess post-exercise oxygen consumption.”
The body also has to replenish its energy stores. It needs to cool down and excrete toxins that may have accumulated during the workout, like lactic acid. Lactic acid is what causes that burning sensation in your muscles when you’re working out really hard. All of these processes take energy. Much of this happens BECAUSE you exercised.
For example, you wouldn’t have too much lactic acid building up in your muscles naturally (unless, of course, there was underlying unrelated health problem). This happened because you exercised. Then, there are the hormones that get secreted during and after your workout which can also influence the number of calories burned. These excess calories are being burned after exercise, but we don’t know which of these processes most contribute to this afterburn effect.
Do Exercise Intensity and Duration Affect EPOC?
We may not know why some experience this afterburn effect and for how long the effect lasts, but most researchers agree that exercise intensity seems to be very important.
It's hard to say how long you need to spend working out and the types of activities you need to perform to maximize this effect.
For example, it’s possible that splitting up your routine into “split sessions” may increase this afterburn effect. Let’s say you normally work out for 50 minutes all at once. A split session might mean you work out for 25 minutes in the morning, then 25 minutes in the evening. Some studies have found that this may increase the number of extra calories you burn after both sessions. Researchers have also found that resistance training may increase post-exercise oxygen consumption more than doing cardio. In fact, lifting heavy weights may increase this afterburn effect more than lifting lighter weights for more reps.
The common theme seems to be to increase the intensity somehow, some way. If it’s safe for you to do so, increase the intensity of your workouts to the point where you fail the “talk test.” Failing the talk test is the goal.
Here’s what I mean: imagine you’re in the middle of your workout and someone walks up to you and asks you if you’re done using that dumbbell. Are you able to respond to them? Or are you breathing so heavily that even muttering a yes or no would be nearly impossible? If you are unable to answer the question, you failed the “talk test.” This means you are working at a high intensity. This seems to be important for maximizing the afterburn effect.
How Long Will the Afterburn Effect Last?
No one can say for sure. If someone claims that after doing their workout you’re going to experience excess post-exercise oxygen consumption for 5 hours, 24 hours, 36 hours, or whatever, they’re lying. This is because it’s nearly impossible to know for sure.
Many studies don’t account for other factors that may influence excess post-exercise oxygen consumption.
These factors include things like:
- time of day
- other unstructured activities folks participate in throughout the day
- food consumption
- caffeine intake
- ambient temperature
There may be differences between each person when it comes to how many calories are burned after exercise and for how long. But the research and consensus seems to be that this afterburn effect may last anywhere from 1 hour after exercise up to 48 hours, depending on the person.
If you want to potentially experience this effect, think about increasing the intensity of your workouts.