why at penn do they run in lane 4

it's lane 5 (which is measured at the 400m), because the shorter lanes (1-4)were added, so more relays could be run at once, on an inside stagger.

The stadium is very old and when it was built there were 4 lanes. To add more lanes for the shorter races (100 - 400) they couldn't add them on the outside because of the preexisting brick wall that surrounds the track, so they added the lane on the inside of lane 1.

When I was in college there were freshmen every year that would go down to the track run a 400 in lane 1 and brag about the fast time he just ran. They would never believe you when you told them that they ran less than 400 meters.