During the week, I do incline speedwalking to build up my calf muscles and improve cardio. This helps save my knees, which would take a beating if I tried to run every day.
But, on Saturdays, I drive to the gym (it's still winter here in Michigan) to do a run on the treadmill at a 15-minute/mile pace.
I realized this past Saturday as I was driving in that I was nervous about the run! Would I be able to do last week's miles plus another quarter mile, would my shoe be tied too tight, did I eat the right morning food, would I be low on energy, when I hit the wall would I be able to get through it?!!
Then it struck me that I would feel this way times ten on my way to the real race! And that dealing with my Saturday nerves every week was going to be good practice for race day.
So I encourage you to challenge yourself with a weekly test of miles/pace. It's good practice for dealing with nerves, pacing, hitting walls, and feet pounding!
(And if you're wondering, I did run 3.5 miles at a 15-minute mile pace. It wasn't easy, but it wasn't as hard I imagined it would be. Next week, 3.75 miles ... I don't know ... I'm already getting nervous!)