For years it’s been assumed that you eliminate more lipids in the magical fat-burning zone—exercising between 68 and 79 percent of your maximum heart rate—than when you really exert yourself. Why? Because, the theory went, low-intensity exercise allows the body to fuel itself from the midsection rather than from readily available food calories.
But a report by David Nieman, a professor in the Human Performance Laboratory at Appalachian State University in North Carolina, showed that strenuous exercise burns more calories per minute than easy sessions. Which isn’t surprising: higher intensity equals more calories. But that study also determined that intense exercise increases your metabolism for up to 14 hours afterward. In other studies, light-duty exercise produced no such caloric afterburn. “We’ve become a nation of exercise wimps,” Nieman says. “Too many people don’t bother or are afraid of exercising hard. But intensity is probably the only way to lose weight with exercise.”
Get over it: Start sprinkling high-speed intervals into your slow runs. Do hill repeats on your bike. Try to maintain a heart rate at or above 80 percent of your max for about 45 minutes several times a week.