Running Outside vs. Treadmill

My sister asked me to go run with her the other day, I am used to running on treadmills but we dont have a 2 person treadmill so we decided to go run outside. After about a mile my shins were killing me, so I just gutted it out and finished the run. This just made me apprciate how great my Nordictrack Reflex Deck is!!!! I can run for as long as I want and I have no issues with my shins or legs hurting.