Burn, baby, burn! One of America's top exercise scientists tells you how to keep the metabolic fires stoked

Muscle & Fitness/Hers, March, 2004 by William Kraemer

lIKE MOST PEOPLE, you probably love the idea of "buy one, get one free." So you'll probably love the concept of exercise afterburn, or as we scientists call it, excess post-exercise oxygen consumption--EPOC, for short. Afterburn, which we've been studying at my lab at the University of Connecticut, refers to the extra calories you burn once you stop exercising. Theoretically, your metabolic fires stay stoked for a period of time after you've unlaced your workout shoes and headed for the showers.

What a concept. But is it real? Can we measure it?

You'll always burn the majority of your workout calories while you're actually moving, but my research does show that exercise can provide an afterburn effect. Here are some tips for burning the most calories after--and during--your workout.

GET OUT OF THE "FAT-BURNING" ZONE

For years, fitness instructors told their clients that the best way to lose weight was to do longer, slower workouts, keeping your heart rate at the low end of its training range. You still see this "fat-burning zone" referred to on some heart-rate charts and cardio-machine programs, and you still hear a few unenlightened trainers quote this theory as gospel.

It is true that you burn a greater percentage of your calories from fat when you keep your pace slow and steady than when you really get your heart pumping. (During high-intensity workouts, you burn more carbohydrates as fuel.) However, here's the mathematical reality: Your total calorie burn--the number that really matters for weight loss--will be higher if you push yourself a bit. Let's say you walk for 20 minutes and burn 120 calories, 90 of them from fat; this doesn't compare to running at a fast clip for 20 minutes and burning 240 calories, 120 of them from fat. What's more, research shows that unlike tougher workouts, low-intensity exercise offers virtually no additional caloric afterburn. Your metabolism returns to normal within minutes after completing a leisurely workout session.

That's not to say that long, easy workouts don't have a place in your routine. Any calories you burn can help with weight control. Plus, if you're injured, doing a recovery workout or getting back to working out after a layoff, slow and steady is probably the way to go for a while.

PUSH INTO THE MODERATE ZONE

Once you begin exercising at 60 to 75 percent of your maximum effort, you'll see a significant bump up in calories burned per minute during exercise. My studies show that this exercise intensity also seems to be the threshold at which you begin burning those bonus calories. Exercising at this level can provide an afterburn period of several hours. The actual number of extra calories you burn depends on your body weight and fitness level, but it can be up to 50 calories or more. This is the intensity at which you probably want to do the bulk of your cardio training.

SPEND TIME IN THE HIGH-INTENSITY ZONE

My research shows that you'll burn the greatest number of calories during and after aerobic exercise when you exercise at 75 percent of your maximum effort or above. If you do very high intensity training, like sprints or intervals, your metabolism can stay elevated for days. Some of my studies show you can burn up to 200 additional calories this way. However, harder workouts are harder on your body. If you overdo them, you may wind up overtired, overtrained, chronically injured or all of the above. For this reason, it's best to limit your very high intensity workouts to once or twice a week.

HIT THE WEIGHT ROOM

Muscle tissue is a very active, metabolically demanding tissue, especially compared to slow and sluggish fat. If you want to increase your body's ability to burn calories, even while at rest, you need to pack on some lean muscle mass. How significantly you can pump your metabolism is a matter of much debate in current research--some studies show each extra pound of muscle can burn as many as 50 calories a day, while others show as few as 15 extra calories per pound. However, we experts agree that even if the number of extra calories burned is small, every little boost helps when you're trying to lose weight and maintain weight loss. My lab, as well as others, has also found some evidence that hardcore weight-training workouts deliver a decent afterburn, as well.

The most efficient way to pack on some sexy, healthy extra muscle is by pumping iron. I've found that you'll get the best results if you do at least two total-body resistance workouts a week, working all your major muscle groups, and if you lift weights that are heavy enough to make your muscles fatigue within eight to 12 repetitions per set. To build more muscle faster, you can include one heavy weight-training workout a week, using weights that only allow you to push out three to five reps per set. A beginner may pack on about three pounds of muscle after three months of consistent weight training, although gains tend to come more slowly for advanced lifters.

BY WILLIAM KRAEMER, PHD, CSCS, FACSM