I have been wondering about this for a little while. I was looking at Runner's World on-line and saw one of their suggestions for a tempo run is warming up for 15 min. then running faster than your normal pace for 20 mins. then cooling down for 15 mins. The purpose being to teach your muscles how to use oxygen differently. I do interverals (4 mins faster w/ 4 mins. recovery 3 or 4 times) and want to change it up with some tempo runs but all my running routes have hills in them. My question is should tempo runs be done on a track? It seems counter productive if I encounter hills and my speed drops.