Exercise Afterburn: Calories keep churnin’ and burnin’ after the sweating stops

Your workout is over. You’re back at your desk or at home carrying on with life, you know, making dinner, pushing papers, or trying to get the kids to eat their broccoli.

However, your body — silently, efficiently, perhaps slyly — is still burning calories. Even after most exercise is over, calories continue to get gobbled – a fact proved again in a study published in September 2011. Some call it “afterburn.” For the record, exercise scientists call it “excess post-exercise oxygen consumption,” or EPOC. OK, we’ll stick to afterburn.

Pretty cool you can do nothing and still keep the fires burning. But the level, type and length of a workout have a big effect on the quantity of afterburn. Adventure Network+Total Fitness Network has updated this column, originally penned more than a decade ago, with the findings from a September 2011 study in the American College of Sport Medicine’s journal, Medicine and Science in Sports & Exercise. In this 2011 study, participants spent a day doing utterly nothing in a sealed chamber that measures every last fragment of what the body uses and produces to gain an exacting calorie consumption reading for the day (researchers call it simply “resting”). Then the participants – in this case, 10 men, ages 22-33 — spent another day in the chamber. This time they exercised for 45 minutes, and then they just sat around – resting. Researchers could trace the calorie use during and after exercise and compare totals to the earlier day just resting.

Here’s the nitty gritty:

How intense must activity be to get an afterburn? — The latest research shows that you’ll get a substantial bang for that exercise buck if your activity is pretty intense or about 85 percent of your maximum heart rate (for the tech hounds, the study noted its subjects had a mean VO2 max of close to 73 percent, which is approximately equal to the 85 percent max heart rate). That’s pretty intense and not for beginners, for sure. Past research has shown that you’ll get some afterburn at a lesser intensity but not enough to jump in glee unless it’s about 75-80 percent of your max heart rate. In other words, you can’t stop and smell the flowers during your workout; you need to be sweating, breathing hard, and getting your heart pumping. If you rely on a rating of your perceived exertion using a 1-10 scale instead of heart rate, the 85 percent reading would be about 6-7, while 75-80 percent would be about  5-6 on the scale.

How long does it have to be? — Even 20-40-minute workouts can earn you some extra calorie use, but not huge amounts. Past studies showed you’ll get the most out of a session that’s at least 60 minutes. In the most recent study, participants did 45 minutes of intense cycling. Researchers indicated the findings would likely apply to any type of intense and continuous workout of 45 minutes, including soccer or running.

How much extra burn do you earn? –Past research indicated that 60 minutes of moderate to vigorous activity would nearly double the afterburn compared to a 20- or 40-minute session. Past studies had found the post-exercise burn could account for an extra 80-100 calories over the first three hours afterward. Now that doesn’t sound like much, but if you gain an extra 90-calorie expenditure, four times a week, that’s 360 calories. Keep that up for a year and you’ve lost an extra 5 pounds or so.

The newest findings show even more benefits in the calories-out part of the formula: The men in this study chowed through an additional 190 calories (+/- 71.4) during the 14 hours after exercise. Considering they used 519 (+/- 60.9) calories during exercise, the total came to 709. In other words, the post-exercise burn added more than another third (37 percent) of that used during the exercise itself. That’s a lot more substantial than earlier studies have found.

Could the afterburn last longer? — One study published in 1999 showed that fit people continued to burn more calories at least 39 hours after they stopped exercise, and that their bodies chose to use nearly double the fat during that time than in inactive people. Whatever the exact length, you can assume the more intense and longer the activity, the longer the afterburn will last. In all cases, it will start higher and slowly taper off over at least several hours. (see chart, right, that showed the timeline of calorie consumption in the September 2011 study)

What if I workout twice in one day? – You’ll probably burn more than if you workout just once, even if the sessions are shorter. That’s because your inner fires use up the most right after you’re done, then slowly die out. So you’ll get that immediate hotter burn twice before it turns into a slowly dying smolder.

What if I’m bigger or smaller or have more or less muscle? The men in this study weren’t all skinny pro cyclists. Yes, they had to be able to complete an intense 45 minutes of cycling but size didn’t play a role. They weighed from as little as 137 pounds up to 325 pounds, with a percent body fat ranging from 9.4 percent to 39 percent (note that more than about 32 percent is considered obese). That probably accounts for the range in calories used in the study, i.e. the bigger you are, the more you normally use. Study author David Nieman also noted that although the study participants were men, the results should also apply to women, who are often smaller in stature.

Oh, and … well … why? — They don’t know. At least not exactly. They speculate that it has something to do with increased levels of certain hormones circulating in the system, changes in the way the body uses fat or how it recovers from decreased muscle glycogen, or changes in body temperature. They also don’t really know if the body chronically adapts to this or simply kicks in the effect after individual workouts.

But, hey, who are we to complain. Keep it vigorous, the longer the better, and cash in for hours after the sweating’s done.

-Therese Iknoian

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The “Coach,” Therese Iknoian, has her Master’s degree in kinesiology with an emphasis in exercise physiology and is an American College of Sports Medicine-certified instructor. To read more about Therese’s coaching, outdoor and fitness background, click here.