Lifting increases the calories you burn while you're sitting on the couch. One reason: Your muscles need energy to repair and upgrade your muscle fibers after each resistance training workout. For instance, a University of Wisconsin study found that when people performed a total-body workout comprised of just three exercises, their metabolisms were elevated for 39 hours afterward. What's more, they also burned a greater percentage of their calories from fat during this time, compared with those who didn't lift.
But what about during your workout? After all, it's considered common knowledge that jogging burns more calories than weight training. Turns out, when Christopher Scott, Ph.D., an exercise physiologist at the University of Southern Maine, began using an advanced method to estimate energy expenditure during exercise, his data indicated that weight training burns more calories than originally thought—up to 71 percent more. Based on these findings, it's estimated that performing just one circuit of eight exercises—which takes about 8 minutes—can expend 159 to 231 calories. That's about the same as running at a 6-minute-mile pace for the same duration.
3. Your Clothes Will Fit Better
If you don't lift weights, you can say goodbye to your biceps. Research shows that between the ages of 30 and 50, you're likely to lose 10 percent of the total muscle on your body. And that number will double by the time you're 60.
Worse yet, it's likely that lost muscle is replaced by fat over time, according to a study in the American Journal of Clinical Nutrition. The scientists found that even people who maintained their body weight for up to 38 years lost three pounds of muscle and added three pounds of fat every decade. Not only does that make you look flabby, it increases your waist size. That's because one pound of fat takes up 18 percent more space on your body than one pound of muscle. Thankfully, regular resistance training can prevent this fate. Just remember this muscle motto: Use it, so you don't lose it. After all, nothing good comes of that.
4. You'll Keep Your Body Young
It's not just the quantity of the muscle you lose that's important, it's the quality. Research shows that your fast-twitch muscle fibers are reduced up to 50 percent as you age, while slow-twitch fibers decrease less than 25 percent. That's important because your fast-twitch fibers are the muscles largely responsible for generating power, a combined measure of strength and speed. While this attribute is key to peak sports performance, it's also the reason you can rise from your living room chair. Ever notice how the elderly often have trouble standing up? Blame fast-twitch muscles that are under-used and wasting away.
The secret to turning back the clock: Pumping iron, of course. Heavy strength training is especially effective, as is lifting light weights really fast. (Hint: Any exercise with the word "explosive" or "jump" in its name is ideal for working your fast-twitch muscle fibers.)