I'm 36 and have quite a few years of mileage and distance work under my belt. I always considered myself a middle distance to distance runner (800-3200 or so). In some recent past seasons I would run the 400 and even the 200 at some early season meets and switch over to the 800 near the end. I had some relative success with this and figured the speed made me sharp and thus made 800 pace feel "easy." I began to wonder if the success that came from racing this way could also come from training this way. If I took a few seasons and basically trained like a 400 runner could this ultimately make me a better 800 runner down the road?