i believe that alot of aerobic work is needed, even as a kid, but it doesn't all have to be running; soccer, basketball, circuits etc can let the kid aerobically develop without making them a slow twitch machine. el g and aouita were soccer players. juantorena was a basketball player. mottram did triathlons. alan webb.
i think, for the 800 specifically, that all the supplemental work is what is going to give us the superior running economy witnessed by the kenyans. aerobic running is important, don't get me wrong, but we need to get efficient at race pace. running alot at race pace is one way, weights/circuits/plyo's/mobility/core work is another.
Anthony may know this, but in many sports outside of running, the periodization they use is in this order; Get strong, Get fast, Get fit. That is, develop the strutcure of the body in a way that can handle fututre training, then develop speed, then attempt to hold that speed. This can be applied over the years too; ages ?-15 lots of other sports and general strengthening // ages 16-18 develop 400m speed with fast speed sessions, plyo's etc // ages 19-? attempt to hold that speed for longer distances. any thoughts?