@lamnhi This reply demonstrates something you don't mention as much in your post (or are just pretty humble about): superhuman motivation. I was running with a friend tonight and we're in relatively similar shape (comparable heart rate at the same pace, run together often, etc.) but he flat-out smokes me at the very end when we're sprinting the last few blocks home. I'm sure it has something to do with lactate threshold and other stuff but more than anything he just has an insane drive that helps him push past the pain. It seems you do, too, and that's really not a small factor in getting shredded in such a short amount of time.