Burn More Calories in Less Time

An hour of play keeps the pounds away. That's the word from a Harvard study that seeks to finally settle just how much daily exercise it takes to fend off weight gain. But here's the fine print: Scientists found that the secret to staying slim for the 30,000-plus women they followed was more about calories burned, not time clocked. In other words, do a tougher workout -- like running at a 10-minute-mile pace -- and you'll need only about two hours total a week to melt enough calories (1,280, based on a 140-pound woman) to save your size, compared with the roughly seven weekly hours it would take at a 20-minute-mile walking pace.

The women in a recent Harvard study who successfully maintained a healthy weight completed a certain total of weekly exercise that was tallied in METs (metabolic equivalents), a scientific measure -- used to calculate calories burned -- of how much effort is involved in any given physical activity. To reach the magic number of 21.5 METs a week, you could do a 7 MET activity, like playing soccer, about three hours a week or a 10 MET activity, like swimming fast freestyle laps, about two hours a week. Use the METs chart below to tab up your weekly pastimes.

Originally published on FitnessMagazine.com, June 2010.