Check out what Dr Phil Maffetone and his partner Dr Coralee Thompson have to say about the brain, stress and music as they were featured on the Renegade Health Show recently.
I reckon listening to my iPod while running might contribute to my health as much as the running itself. It's the exercise that makes me fit of course, but if I go too hard it might actually add to the stress levels in a harmful way. I've certainly been there, done that!
By the way, the fifth edition of Phil's old book In Fitness And In Health should be coming out at the end of this month. I bought my copy about 15 years ago, and even back then it was advertised as the new and revised edition! The book is still highly recommended, so keep your old eyes peeled on it.