David Nieman

Vigorous exercise produces ‘afterburn’ bonus

May 08, 2012

One of the obvious rewards of exercising hard is that you burn up calories while you’re doing it. That added calorie combustion helps you stay trim and may even help you lose weight, although you also have to watch the number of calories you put into your body.

Exercise scientists have found that vigorous exercise has an added bonus: an ‘afterburn’ of revved-up metabolism — and the calorie-burning needed to supply it — that continues after the huffing and puffing are over. Some studies have indicated that this lasts 20 to 30 minutes and burns 30 or so calories, which is fine but really not all that impressive. But researchers in North Carolina have reported some results that are.

They recruited 10 young, healthy male volunteers and used a sophisticated metabolic chamber the size of a small bedroom to measure their oxygen consumption before, during, and after exercise. Oxygen consumption is a reliable indicator of metabolic rate and calorie expenditure. Not unexpectedly, the young men burned up an average of about 500 extra calories during 45 minutes of hard pedaling on a stationary bike. What was surprising was that their metabolisms remained elevated for the next 14 hours, even though they were inactive and even as they slept during the last three and a half hours. The study subjects each burned an average of 190 extra calories during those 14 hours, which is 40 per cent of the extra calories they burned up while cycling.

How fast did they have to pedal to achieve this afterburn? Fast enough to use 70 per cent of their maximal oxygen uptake, which exercise scientists call VO2max. We asked one of the researchers, David Nieman, to put that in more concrete terms, and he told us most people would describe it as pedaling “hard or somewhat hard,” although the better shape you’re in, the easier it is to achieve and maintain 70 per cent VO2max. So maybe like a spin class? Only if there aren’t any rest intervals, Nieman said, because to produce that long of an afterburn, it has to be a vigorous workout of “unrelenting intensity.”

Still, the take-home message here is that metabolism stays revved up after a hard workout, and that extra calories get burned as a result. Lately, exercise advice has emphasised the health benefits of moderate exercise, like brisk walking. But there’s a lot to be gained from pushing yourself a little bit harder if you can, especially when it comes to burning calories and controlling your weight

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