It's interesting how strongly music affects mood, specifically in regards to working out.  Certain songs can make me push my body past its comfort level, though I'll usually feel the effects later or the next day.  But what's most interesting is that once a song becomes a workout song, it can't be undone.  That song is forever a workout song.  Even if I hear it in a non-workout setting, it'll increase my heart rate and make me start sweating a little.  And since I dabble in kickboxing, pretty much all my workouts involve hitting things.  So watch out.