An audio player comprises a means of dynamically sensing the rate of repetitive motion of the user, a means for storing digital music files, a means for retrieving and dynamically playing at least one of said music files at a rate approximately equal to the sensed rate of repetitive motion of the user, and a means for dynamically calculating and displaying information and/or statistics regarding at least one of the music file and the user. Such a device can play music, or other audio content with a repetitive beat, in substantial synchrony with the repetitive motion of the user. The device also allows the user to dynamically choose or change the music file playing. The device may detect, calculate, and display to the user various information.