Is it true that your body continues to burn extra calories for 12 hours after you've worked out?
Yes. "After vigorous exercise, we've seen caloric expenditure increase for up to 48 hours," says exercise physiologist Tom R. Thomas, Ph.D., director of the exercise physiology program at the University of Missouri in Columbia. The longer and harder you work out, the greater the post-workout metabolism increase and the longer it lasts. Subjects in Thomas' research burned 600-700 calories during one hour of running at about 80 percent of their maximum heart rate. During the next 48 hours, they burned about 15 percent more calories -- 90-105 extra -- than they otherwise would have. About 75 percent of the post-workout metabolism increase occurs in the first 12 hours after exercise, according to Thomas.
Weight training does not appear to offer as significant a post-workout metabolism increase as intense aerobic exercise, Thomas says, probably because of the rest between sets. A number of studies suggest that, after a 45-minute weight-training session -- three sets of 10 reps per exercise -- resting metabolic rate is increased for 60-90 minutes, burning an extra 20-50 calories. However, keep in mind that strength training is an excellent way to boost your resting metabolic rate (the number of calories your body burns at rest). While aerobics appears to offer more of a post-workout spike in metabolism, strength training enables you to develop muscle mass, which, in turn, increases metabolism overall.