I can't remember who, but I read of one of the world's old great running track w/o's near daily. Could've been Zatopek or more likely one of the Fins. Can't remember and not that important. My question: to the extent you're running twice daily, what's the benefit to running track w/o's during one of your sessions near daily? Specifically, 12 x 400's, w./ decent warm up, cool down. Thanks.