Hello PJ, and thank-you for keeping the dialog going here. I have been camping for a week, and just got back this morning, so I have a lot of email and forum dialog to catch up on.
I believe the best person to respond to your inquiry is Stu, as he has been an athlete most of his life. I have had several conversations with him about the "runner's high" or the "zone." From reading and hearing from athletes about this experience it is clear to me that the the "runner's high" or the "zone" is essentially the experience of no-mind which is a characteristic of the second stage of the religious experience.
To support your experience of finding increased depth in meditation following a run; from spending more than 4 decades developing the 8 stages of the religious experience it has become clear to me that to traverse these stages of the religious experience one must learn to relax deeply.