How to get motivated to exercise

Unfortunately my busy schedule is rather overloaded with writing on the Net these days, and even one hour's exercise isn't easy to fit in. For some reason being healthy just isn't enough of an incentive to do exercise just for its own sake, particularly when, for example, to go swimming I have to get up at six am on a cold morning; or have to walk in the rain for half an hour, or go on the treadmill and have to do something to occupy my mind. However, my fingers get plenty of exercise, so that's a start!