Bonus calories or fitness myth? The truth about afterburn

Whether you’re just getting into exercise or you’re already scrupulous about fitness, you may have heard the term “afterburn.” Also called excess post-exercise oxygen consumption (EPOC), afterburn refers to a period of time after you exercise when your body uses extra oxygen. It may last for hours or even longer than a day, depending on the type of exercise. You do. During that time, metabolism is believed to speed up, burning additional calories.

For over a century, the afterburn phenomenon has been intensely debated in the fitness and medical communities, with countless studies attempting to explain and measure it. But questions remain: How many calories are we talking about? And can they contribute to weight loss?

Expert opinions vary, as study results have contradicted each other due to differences among participants like weight, sex, and training levels.

But most reliable studies do agree on one thing: There’s a relationship between exercise intensity and afterburn. After a certain intensity level is reached, that relationship turns into a direct correlation—meaning the harder you work out, the greater the afterburn.

What’s the right level of intensity?

To activate afterburn, research suggests that the target exercise intensity level should be around 50 to 70 percent of a person’s VO2max, or the maximum amount of oxygen used by an athlete while performing an activity. You can tell you’re at around 70 percent VO2max when it’s too difficult to both breathe and carry on a conversation at the same time.

In a 2011 study published in Medicine & Science in Sports & Exercise, researchers at Appalachian State University and UNC Chapel Hill used methods that avoided many of the weaknesses of prior studies. Their work helped to shed new light on afterburn.

The study took place in a controlled environment called a metabolic chamber—a room that can monitor the calories burned by a person inside. Young male participants were asked to spend two 24-hour days in the chamber. On the first day, to measure their calorie use at baseline, they performed the bare minimum of activities of daily living. On the second day, they repeated their routine, but added a 45-minute session on a stationary bike. They cycled at about 70 percent VO2max and initially burned around 519 calories. Then, remarkably, over the next 14 hours, they continued to burn an additional 190 calories.

How hard you push is key

The intensity of exercise is important to increase afterburn, with more vigorous exercise leading to greater and longer-lasting EPOC in the hours and even days after the workout. Intermittent aerobic training—like pushing hard for 30 seconds repeatedly during an otherwise moderate exercise session, also known as interval training—also seems to provoke EPOC more powerfully.

Research demonstrates that intensity level has a greater effect on calorie usage than how long a workout lasts. In fact, one study attributed five times more EPOC to intensity level than to both workout duration and total work performed. This is consistent with evidence that shows longer afterburn periods after interval training.

The same appears to be true for resistance training (such as working with dumbbells, weight machines, or rock climbing): the higher the difficulty level, the greater the afterburn.

So if you’re looking to harness afterburn with your next cardio session, consider alternating between moderate-intensity exercise and intense sprints, rather than moving at a consistent pace. And remember to hit the weights, too, which can not only help you burn calories but also help you build and maintain muscle, crucial for your body over the long haul.