Wear sunglasses. You’ll not only look cool, you’ll stop squinting and relax your face. Doing that will set off a chain reaction… and you’ll end up relaxing your neck, shoulders and upper body. That’s according to marathon running coach Andrew Kastor. He says that even a tiny bit of tension in your upper body can throw off your form, which means you won’t stride as powerfully. And tight muscles work harder and use more energy than relaxed ones – so you’ll burn out more quickly. So wear some shades and leave everyone in your dust.