Hill Running
As was stated earlier, a useful tool in training can be to run on different surfaces, as it relieves the constant pressure of one kind of surface on the individual.
Hill running is an extension of this as it allows for running on a different surface and also teaches a slightly modified technique that is more aggressive and requires more knee lift.
Hills is something that can be an asset to anyone, whether for the duration of a sprint race or for a finishing kick in a distance race. It has more obvious benefits for those who are going to do road races or cross-country as it is very unlikely that any of these races will be entirely flat.