The Average American spends half his waking hours seated-on a couch, in the car, and, yes, at a desk. We're all going to die, but several new studies have found that too much sitting is killing us faster. Seated, we burn fewer calories, our muscles get weaker, and, soon enough, our metabolism slows, we burn less fat, and become especially prone to heart disease. The solution is simple: Stand up [every 20 minutes is an oft-cited rule]. But breaking a habit is hard, and can look silly.