It comes with a dedicated music key which allows you to play, pause or change songs without even opening the lock or taking the phone out of the pocket. (droidholic.com)
If you need motivating music, there's even an app that changes the songs on your phone to help you find a fitting tempo. (infinitelifefitness.com)
Doing so will change the song over to your song along and create a nice little explosion. (playstationlifestyle.net)