Then, last summer, I gained more than 10 pounds. The weight gain was perfectly explicable: I had a new job, came home each evening ravenous and depleted and regularly needed a cheese plate and a tequila beverage to revive before dinner. This time, my beloved gynecologist issued a gentler warning. Weight training, she reminded me, is one of the best ways to combat the weight gain that often accompanies aging. In addition to building muscle strength and bone density, it can also boost metabolism.