Sprints to mid-distance. That's the question here. How and when do you determine that a 400m runner needs to move up to 800m? If a 400m is running slow(er) times, but is built bigger, he can't go up to the 800m. Smaller framed runners like Jeremy Wariner have almost that prototype 800m build but he never went up to that distance officially (1:53 was his PR). So how do coaches make that decision?