How to Build a Better Running PlaylistOne simple way to get swift: Turn up the tunes. Research shows that it can be a great motivator. To build a better playlist, download these music apps.PaceDJ: Have a favorite running tune, but its tempo doesn't fit your workout? No problem. This app will speed up or slow down the song to match your target pace. ($3; pacedj.com)TempoRun: Once you select your pace (speedy or snail), the app analyzes the songs in your library, then categorizes them by beats per minute. ($3; temporunapp.com)FitRadio: Choose a genre plus your target pace (for speedwork, that's between 120 and 140 beats per minute), and this app will formulate a playlist to match your taste and preferred tempo. (Free; fitradio.com)