Do You Keep Burning Calories When the Exercise Stops?
Vigorous exercise can keep our bodies warm for hours after we stop. But does the afterglow come from burning more calories or something else?
The Institute of Medicine (IOM) was so convinced it was because of a post workout boost to the metabolism that they proposed increasing the amount of calories burned from any exercise by 15%. Using the IOM suggestion, if you did an exercise that burned 500 calories, you would get to deduct an additional 75 calories from the afterglow.
In 2008 tests were conducted to confirm the boost, but the numbers didn't match up. Some subjects saw their metabolism jump up and burn significantly more calories, while others saw no post workout benefit at all. We wanted to find out why the huge difference, so we decided to dig a little deeper into the studies and the numbers. We found two things that burn more calories and two theories why you stay warm, even when the calorie burning stops.
The first factor in burning calories after exercise is how fit you currently are. When young, physically fit subjects in their 20s and 30s did 45 minutes of vigorous cycling, they burned about 519 calories. Over the next 24 hours, they burned an additional 190 calories (37% more) from their elevated metabolism.
When less physically fit subjects were tested, the results were significantly lower. In some studies the metabolic boost was under 5%, lasted less than five minutes or in some cases was non-existent. The more fit you are, the more calories you're going to continue burning when you finish your workout.
That's not all you have to consider, intensity is another factor. When subjects were put on a simple resistance training routine, they were divided into two groups. The first did one set of ten exercises. The second did three sets of ten exercises. After the workouts, both groups burned an additional 100 calories per day. Even though the second group had three times the volume of exercises, the calories burned afterwards were the same.
It was a different story when the intensity was increased. High intensity workouts that significantly increased heart rate, also tended to keep burning more calories once the exercise stopped. The lesson is, if you're trying to burn more calories you need to increase the intensity.
(Increasing the volume of a program will burn more calories DURING the workout, but both high and low volume workouts tend to burn the same amount AFTER the exercise.)
There was still a problem. What about those subjects who didn't see any significant calorie burn when they stopped exercising, but were still giving off heat? What was causing the elevated temperature? In some cases the excess heat lasted for hours.
Glenn Kenny, a professor in the School of Human Kinetics at the University of Ottawa decided to find out why. So he built a million dollar machine (the only one of its kind in the world) that measures changes in a body's heat loss, minute-by-minute.
Using this machine, Dr. Kenny learned that when a body's core temperature goes up during exercise, it has a hard time getting rid of the heat. There are two leading theories why.
One, when you stop exercising, your circulation goes down and heat dissipation drops. You still feel hot, but you're not actually burning any extra calories. Your body is just moving the warm blood to the surface venting excess warmth. Unfortunately you won't lose extra weight. The heat is just a sign your core is reducing its temperature.
The second theory is that when the body's immune systems kick in to repair muscles, they generate heat-producing energy. The more muscle that's torn down, the more heat all those warm repair cells produce.
What does all this mean for the average person exercising? If you're trying to lose weight, concentrate on higher intensity workouts to burn more calories. Then as you get in better shape, the afterglow following a workout will increase.
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