What do muscle mass and strength have to do with how well we age?
After 30, your muscle mass dwindles some 3-8 percent each decade. Once you hit 60, these losses accelerate even more quickly. The consequences are far more serious than a change in your appearance. Declining muscle mass doesn't simply mean your shoulders are less toned or that you can't achieve the same results in sports that you did as a teenager. These muscle changes have implications that are much bigger than your new pant size. The effects are serious and far-reaching. They determine how healthy and active you'll remain for the rest of your life.
Decreased muscle mass means you'll burn far fewer calories. If you take in the same amount that you did when you were younger, you'll start accumulating body fat. Your muscles require a lot of calories to maintain: Think of them as a bunch of high-strung, active family members visiting your home. They're always up, moving around. As a result, they're hungry and require a lot of food.
Imagine that these demanding visitors gradually leave, one by one, and the remaining folks start lying on the couch. This is like your muscles becoming smaller and weaker. These relaxed visitors don't need as much food, but you keep buying the same amount of groceries that you bought when you had a big group of active guests. This is like eating the same amount of calories you did when you had more muscle. Gradually, your cupboards and refrigerator overflow with unused food. This is like storing up fat from those unnecessary calories.