Basically, my mile PR is 5:03 but for three 2 milers in a row, my first mile was as follows: 4:59 (10:23 2 mile),5:02 (10:23 2 mile), 5:07 (10:27 2mile). Now I understand that all of these are big positive split races, but I'm wondering why I've broken 5 for my first mile in the two mile, but yet I've never actually gone sub 5 in a regular mile race.