Assigning personal theme music to earbuds for exercise encouragement

I want my earbuds to play when I move as an encouragement to exercise. Any idea how to do this? I deliver mail and I want my earbud to play some sort of music each time I jump out to deliver a package. It would be totally awesome! We all probably have work to perform that is less than desirable……setting the music would be so empowering.

[Re-Titled by Moderator]

Original Title: Personal theme music