After a long hiatus I've started to run again and am training for a marathon relay in May. I've done long races in the past and had success adding speedwork and tempo runs to my training. However, it's all been outside (I live next to a great, flat path that's marked). Has anyone done speedwork on a treadmill? Any tips or workouts to share? I was thinking of trying a few short distance intervals like 400s with a 2 min rest in between. Thanks so much!