Many websites, books and personal trainers claim that strength training will increase your resting metabolism, which means your body will burn calories at a higher rate even when you are not exercising. Some go so far as to say that body fat will practically melt away without dieting because of this revved-up metabolic rate. Fact or fancy?
Mostly fancy. True, strength training can boost resting metabolism somewhat, but how much and for how long depends on how intensely you train. Some studies have found that resting metabolism stays at least modestly elevated for 12 hours or longer; others show it goes back to normal within an hour after exercising. But average gymgoers don’t work out long enough or hard enough to achieve any significant calorie-burning after-effect. More significant are the calories you burn during the workout. Strength training is not unique in this: All exercise—particularly aerobic exercise—can increase metabolic rate to some degree.
It’s also true that strength training builds muscle, and that muscle burns more calories than body fat does. Still, you have to train hard and long to add a significant amount of muscle. And even then, the impact on body weight is usually small. One pound of muscle typically burns five to eight calories a day, though this depends on many variables, according to estimates by Robert Wolfe, Ph.D., professor of geriatrics at the University of Arkansas.
In contrast, a pound of fat burns about two calories. A woman who does strength training three times a week for six months, for example, may gain two to four pounds of muscle. That would result in 10 to 32 extra calories burned a day—not much, considering that you need a deficit of about 3,500 calories to lose one pound.
So it’s not totally surprising that several recent studies of overweight or obese people—including one from Duke University Medical Center, in the Journal of Applied Physiology—found that two to eight months of moderate strength training, done two or three times a week, had little or no effect on weight or body fat, though it did increase lean body mass (mostly muscle) a little.
Strength training: stronger benefits
Whether it helps you lose weight or not, strength training provides many benefits, including not only stronger muscles, but also stronger bones. You may see an improvement in athletic performance, such as in your tennis or golf swing. Stronger muscles can also improve your quality of life, making it easier, for example, to tote a bag of groceries or carry a child in your arms.
And a toned body makes you look slimmer even if you don’t lose weight (you might, in fact, gain weight if you train strenuously and add lots of muscle). What’s more, strength training can help reduce blood pressure, blood sugar and cholesterol, and may even improve cognition in older people.
Words to the wise: A balanced workout should include a cardiovascular (aerobic) workout and strength-building exercises. But if your primary goal is to lose weight, focus mainly on aerobic exercise (such as running, biking, skating or brisk walking) four or more days a week for at least 45 minutes. This burns more calories and is more likely to significantly boost your metabolic rate afterwards than strength training.