You help your heart and lungs get stronger and healthier by doing mind-body exercises — a little or a lot depending on what you do and how you do it. But you won't, or at least you shouldn't, hurt. No grinding knees, complaining backs, pulled hamstrings, or any of those other miseries often brought on by high-impact exercise. And, here's that nice plus again: Being more fit can mean more calorie-burn, too, since toned and fit muscles demand more calories than fat does.