Whether you call it strength training, weight training or resistance training, research now shows that building and maintaining your body’s muscle mass is the key to a staying fit for life. The average 35-year-old man has 18% body fat, but by age 65, he has 38% fat. And the body fat percentage change is even more striking in women. In fact, every decade from age 40, you may lose up to 6 lbs of muscle. You might not have noticed, since the size of your arms and legs often remain the same as when you were younger. But they’re the same size because fat has replaced the muscle.

In fact, your body’s metabolism will likely drop approximately 2-3% each decade after you turn 20. But this doesn’t have to happen! Researchers now believe that reduced muscle size is almost entirely responsible for the gradual decline in your basal metabolic rate. So by maintaining your body’s muscles, you can actually reverse this trend and increase your metabolism.

Strength training is the key to lifelong weight control. Muscle is active tissue, and it burns calories even at rest. Fat doesn’t. Fat stores calories as energy for future use. But dieting alone will cause you to lose muscle first, and then fat. After you’ve lost the weight, your body has less muscle, so your metabolism decreases. Because your metabolism has decreased, it’s harder to keep the weight off, and you may find yourself gaining the weight back, plus a few more pounds. Doctors call this weight cycling, but you may know it as “yo-yo dieting.” You can prevent this vicious cycle by building and maintaining your body’s muscles to keep your metabolism high.