Imogen Heap is awesome. Not only is she a great musician, she is also working on an app called Run Time that customises a run. It takes ambient sounds like breathing, footsteps, traffic and even birds and layers them with a pre-recorded electronic track. The best thing is that the runner can adjust the tempo of the music according to stages of a run: slow warm up, walking, running, acceleration and deceleration. She demonstrates this perfectly in her video.
The app is still in development. Depending on how much it is, I will likely get it. Although, I won’t lope around NYC like a crazy person the way she did.