You read the headlines, like “interval training has an afterburn effect, so after you finish your workout, you’re still burning calories.” Or you’ve heard a personal trainer at your gym maybe say the same thing. And exercise programs have even come out over the last 20 years, with interval training as the centrepiece of the entire program.
So in this article, we’ll cover:
- A definition of the afterburn effect
- Whether it happens or not
- Real-life considerations
What this article will not cover is the debate between interval training and steady state (continuous) training. I covered that in this article.
Original source: here.
What is the Afterburn Effect
The afterburn effect is the idea that you continue burning calories even after your workout is finished. However, for the afterburn effect to occur, the exercise must be of a sufficient intensity. In other words, just going for a walk doesn’t cut it. The scientific term for the afterburn effect is Excess Postexercise Oxygen Consumption (or EPOC).
The theory goes that by creating a “metabolic disturbance” (doesn’t that term sound great?) through sufficiently intense exercise, you create enough microtrauma to the body that it elevates the metabolism for hours (and some say, days) after the workout.
Sounds great from a marketing perspective. “Eat whatever you like, just as long as you exercise intensely enough, you’ll be able to burn off those calories.” Too bad it doesn’t work that way.
Is the Afterburn Effect Real?
So the truth is that yes, the afterburn effect really does exist. There’s no debate about that. The real question is the magnitude of the effect. How many calories do you really burn after (not during) intense exercise? While there’s no general agreement on the exact number, there is agreement on one thing: you don’t burn that many calories after an intense workout.
In one study, participants were divided into 3 groups:
- Group 1 exercised at 29% of their VO2max (their aerobic capacity)
- Group 2 exercised at 50% of their VO2max
- Group 3 exercised at 75% of their VO2max
All 3 groups did it for 80 minutes.
And group 3 did burn 150.5 calories after their workout. But remember 2 things:
- Their workout was intense (75% of max)
- Their workout was long (80 minutes)
Another study found that EPOC ranged from 6% for moderate intensity, and up to 15% for high intensity.
So let’s put some numbers to this. Let’s say you burn 400 calories during your workout. If that workout was of moderate intensity, you will burn 6% more calories after the workout. Six percent of 400 is 24. Now, if the workout was of a high intensity, you will burn an additional 15% after the workout. But 15% of 400 is 60. So the difference between a moderate and a high intensity workout is only…. 36 calories? Yep. This allows you to have an extra spinach leaf. Enjoy 🙂
But wait… just imagine the headlines. If you just manipulate the statistics a little bit, you’ll see that 15% is 150% BIGGER than 6%. What would the headlines say?
Interval training burns 150% more calories after exercise!
As Mark Twain once said, “there are lies, damn lies, and statistics.”
A third study compared high intensity to very high intensity. In that study, there were 3 groups:
- Group 1: did nothing, they were the control group
- Group 2: exercise for 30 minutes at an intensity of 70%
- Group 3: did 20 intervals of 1 minute, with 2 minutes rest between intervals, at an intensity of 105% (so they were exercising above their anaerobic threshold)
And the results:
- Group 2 had an EPOC of 7.1%
- Group 3 had an EPOC of 13.8%
Impressive… not!
Real-life Considerations
So in real-life, we really see that the difference between steady state and interval training is waaay overblown. And besides that, there are a few things to consider:
Consideration #1
In most studies, time between interval and continuous groups is equal. But in the real world, that’s not the case. In the real world, the more intense the exercise, the shorter the duration. After all, you can’t sprint a marathon. So to compare 20 minutes of intervals to 20 minutes of continuous exercise is not totally a valid comparison. Twenty minutes of intervals is a very difficult workout. But 20 minutes of continuous exercise is not that difficult, so people do it longer… 40 minutes… 60 minutes, etc. But to do 40 or 60 minutes of interval training is damn near impossible.
Also, frequency and intensity are inversely related. Whereas you can do low or moderate intensity exercise every day, high intensity can’t be done every day (not long-term, anyway).
Consideration #2: NEAT
NEAT stands for “non-exercise activity thermogenesis.” That is all the things you do in your day that aren’t formal exercise that add up to calories burned. These are things like fidgeting, doing work-related activities, like walking from one floor of your building, to another, etc.
These are not really things you do consciously, so it’s hard to keep track of, but NEAT can add up to crazy amounts. To the tune of 900 calories per day. And yet, for some people, if they really exhaust themselves during exercise, NEAT goes down. You fidget less, you move less, etc. And yet, for other people NEAT is not that affected. There is large person-to-person variation in how exercise affects NEAT.
Consideration #3: Appetite
For a lot of people, exercise stimulates their appetite. For a lot of other people, it doesn’t stimulate their appetite, but they psychologically feel like they can justify eating more because of their difficult workout. Even though the workout burned 500 calories, but they’re eating 800 calories more.
The best thing to do is to go by hunger. Don’t factor exercise into your equation. If you’re hungry, eat. And eat until you feel satisfied. Not stuffed/bloated, but satisfied.
The Bottom Line
So now that we’ve busted the myth (or the “part truth”) about the afterburn effect, does that mean that interval training is worthless? No, far from it. That’s not at all the argument I’m making in this article. Interval training has many things that it does that continuous training doesn’t do (and the opposite is true as well). But when talking strictly about fat loss, and calorie burn, the differences between interval training, and steady state exercise are seriously overblown. In a nutshell: it’s not that big a deal, and there’s really not that much of a difference between the two.
Yes, there are large differences between the two when it comes to improvements in aerobic and anaerobic capacity. But not fat loss.
