"When your body starts to betray you and you feel totally defeated mentally, remember this: You are not this body. You are not these thoughts. You are a beautiful and perfect soul deeply connected to a much larger universe. And running five loops at Barkley is but a drop in the ocean of all of the Self's potential achievements. So. You will keep going.
Try, as best you can, not to identify with the body or with the thoughts. Get connected to something much, much bigger than the small self. Let the mind empty of everything else."