There were some requests to get some more info on my interval specifics. I use a treadmill because it is so much easier to set speed and time than running out in the real world constantly glancing at your GPS watch.

This heart rate data includes my warm up (3 min walk then run 1 min at 5, 6, & 7 mph with 1 min walk between) and cool down (3 min walk) and 3 miles of actual interval running (3 min at 7 mph and 2 min walking both at 0.5% incline).