On post-exercise oxygen consumption. Originally published 2 August 2019. Last updated 15 October 2020.
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.
What is VO2 Max? And How Do You Improve It?
VO2 max is term commonly used in the fitness industry. It’s an abbreviation for “volume of O2 max”, where O2 refers to oxygen.
If you're wondering why oxygen is referred to as O2, when oxygen is found in the air as a gas, it is often found in pairs. If you were to look at the oxygen we breathe under a powerful microscope, you would see that really, it’s two oxygen molecules bound together
So we’ve established that the “V” in VO2 max stands for volume and the “O2” means oxygen. The term “max” is actually a bit more obvious; it stands for maximum.
VO2 max refers to the maximum amount of oxygen you can consume and use at a given time. We like to use VO2 max in the fitness industry because the amount of oxygen your body can consume and use at a given time is directly related to how healthy your heart and lungs are.
Think of it this way: you already know we need oxygen to survive, but we need more of it when we’re working out.
- Our muscles desperately need it to allow us to continue our workouts
- Your brain needs oxygen to allow you to continue to think and process
- Our hearts need oxygen to continue beating
V02 Max Values
Where does all of that oxygen come from and how does it get to all of these areas of the body?
The air we breathe contains some oxygen (along with other gases like nitrogen and hydrogen), which then goes to our lungs, and from there, enters our bloodstream. Once the oxygen enters our bloodstream, we have to rely on the heart to pump that blood that is now rich in oxygen (or O2) out to the rest of the body, like our muscles that so desperately need it when we’re finishing that last hundred meters.
The better, or more efficient, your body can do this, the longer you’ll be able to sustain your workout. This is why VO2 max is a valid and reliable measure of how well your heart and lungs are working–if your body can quickly and efficiently send oxygen rich blood to the rest of your body, then it means your heart and lungs are doing their jobs. Or, said another way, your heart and lungs are in good shape! I can say this differently using “fitness lingo”: you have a high level of cardiorespiratory fitness.
VO2 max (the maximum amount of oxygen your body can take in and consume at a given time) can actually be represented as a number. Once you know that number, you can compare it to values for your age and gender to see how fit you are compared to others within that same age and gender category.
For example, if you are a 31 years old female, and your VO2 max was over 40, your cardiorespiratory fitness is at a minimum, average. Once you get past “average,” the rankings increase to “good,” then “high,” then “athletic,” then finally topping out at “Olympic.”
I should also mention that there are different normative value tables, depending on how your VO2 max is being tested.
How Can You Increase Your VO2 Max?
The best way to do that is to incorporate variety in your training. There are many ways to go about this. Here are some examples:
- If you normally do cardio only, add some resistance training. It could be body weight exercises, lifting actual dumbbells and barbells, using resistance bands… whatever suits you. Why would this help? It forces your body to adapt to something new. This means your heart and lungs have to respond to something they are not used to. This, in turn, makes them more efficient, which is the hallmark of measuring VO2.
- If you already perform resistance training exercises, decrease the rest periods between sets. Why would this help? Again, you’re forcing your heart and lungs to adapt to something different. By giving your body less time to recover, you force your heart and lungs to work harder and become better at supplying your muscles with blood and oxygen.
- When it comes to cardio, change the intensity. If you normally walk for 30 minutes, jog instead. I don’t expect you to jog for 30 minutes straight. Even if you end up jogging for only 5 or 10 minutes and then walk the other 20, that’s fine. Why would this help? You’re forcing your heart and lungs to adapt to something different.
- Lastly, as I always say, be consistent. In this case, be consistent with inconsistency! Try to mix up your workout routines every so often. A good starting point is to change things up once every 4 weeks. For example, if for the last month or so, you’ve only been resting 30 seconds between sets of resistance training exercises, go back to a longer rest period of 2-3 minutes. Then after 4 weeks of following that protocol, change your rest period to 10 seconds between sets. Do that for 4 weeks. You get the idea. The same rules can be applied to your cardio routine. If you’ve been jogging at a medium pace for the past month, start running sprints.