For generations, runners have followed the same rituals to warm up before races or workouts: Start with some jogging, move on to a little bit of stretching, then perform a series of 'strides'—short sprints lasting about 10 seconds that get your heart pumping and kick-start the delivery of oxygen to your running muscles. But do these timeworn rituals really help us perform better? Jack Daniels, Ph.D., isn't convinced. 'What I most often see at races is a bunch of runners striding up and down at a speed that is clearly faster than the coming race pace,' he says. Since these strides are the last thing runners do before starting the event, that inappropriate pace is fresh in their minds. 'And when the gun finally sounds, they 'stride' or sprint right out.' The result: a way-too-fast start followed by an inevitable crash.