Running uphill slows you down more than running downhill speeds you up.
So, you can expect hilly runs to be slower than flat runs. You dont get all of the energy that you expend going uphill back when you run downhill, explains Nimbus Couzin, Ph.D., a marathon running physics instructor at Indiana University Southeast. Thats because when your feet strike the ground on a descent, a lot of energy is lost.
The Exception When you run point to point with a net elevation drop, your average pace should be faster than on a flat course.