Step 2: Get Stronger
Let's be clear: You do not have to be a meathead to have a healthy metabolism. You can keep yours fired by doing enough resistance work to hold on to the muscle you've got, says David Nieman, an exercise physiologist at Appalachian State University, in Boone, North Carolina. "The whole idea is to maintain as much muscle mass as possible as late in life as possible," he says. "Your metabolism will hang in there as a result." That said, you can speed your metabolic rate a little by putting on a few pounds of muscle now. Doing so will never be easier (your natural levels of testosterone and growth hormone are higher today than they'll be in, say, five years), and the added size will act as insurance for later. "A critical factor for muscle aging is reaching your peak possible development when you're younger," says University of Pittsburgh epidemiologist Anne Newman. In other words, create and maintain muscle mass now and you'll have more to lose when age-related muscle loss starts in your sixties and seventies.
There is another reason to dial up strength training sooner rather than later: to maintain the number of muscle fibers. Marcas Bamman, the director of the University of Alabama at Birmingham's Center for Exercise Medicine, has had success building the size of muscle fibers with his 60-and-older research subjects in several clinical trials. ("I can train a 65-year-old for four months and his fiber sizes match people 35 years younger.") But he's had no such luck boosting the number of muscle fibers, the other component of muscle mass. That's because muscles are a "demand-based system," Bamman says. If you're not stressing and training the fibers, some of them will begin to atrophy, disappear, and never come back. So if you've got 800,000 muscle fibers in a quadricep at age 30 (the number experts estimate) and you never strength-train, that number could fall 30 to 50 percent, potentially putting you at 400,000 fibers by the time you're 70. At that point, you can still build a stronger leg with the remaining fibers, as Bamman has demonstrated with his seniors. But your quad will never be as strong as it could have been — or burn glucose quite as efficiently — as if you'd strength-trained through your thirties, forties, and fifties.