1) I am a creature of habit, so music does not factor high in my training equation unless it is running on a treadmill or riding a stationary-bike.
2) Spartan training is absent of the niceties of modern day technology. It is just I, the sound of my footfalls, and the lovely scenery that keeps me company.
3) The sound of my footsteps indicates to me if I am landing heavily, getting fatigued, or losing my form.
4) The sound of footsteps is a metronome of sorts, and allows me to moderate my pace (as I mainly run alone).
5) I am attuned to the sound of my breathing. If I breathe too hard, or am panting, I am exceeding my lactate threshold.
6) Without music, I can focus on other things: other runners, the seaside scenery, background sounds, my heartrate, and my internal state.
7) Competition events disallow the use of iPods and other digital music devices, so train according to racing conditions.