Steven, Where'd you get that number of 60/40? Cause I've seen data showing anywhere from ~85/15 (an/aer) to 40/60. The funny thing...the slower the 400 is run, the more aerobic it is. At the <45 second range (where WRs will be broken), the anaerobic system is contributing >70% of the energy. Link
The faster you run, the more anaerobic energy is used. Of course, this will depend somewhat on the runner, but the bottom line is that the anaerobic system is the dominant one, especially for this caliber of 400m sprinter.
High-speed running performance is largely unaffected by hypoxic reductions in aerobic power
Despite reductions in the aerobic energy available for sprinting under hypoxic conditions, our subjects were able to run just as fast for sprints of up to 60 s and nearly as fast for sprints of up to 120 s. This was possible because rates of anaerobic energy release, estimated from oxygen deficits, increased by as much as 18%, and thus compensated for the reductions in aerobic power. We conclude that maximal metabolic power outputs during sprinting are not limited by rates of anaerobic metabolism and that human speed is largely independent of aerobic power during all-out runs of 60 s or less.
Lots of coaches have different methods of getting results...Clyde Hart, Barry Ross, Charlie Francis...all have their own ways and they all work. From what I've seen, work to increase the aerobic endurance is intended to provide better recovery in training sessions
as opposed to for in-race aerobic endurance. For a 400, the aerobic system can be trained pretty much exclusively through intensive/extensive tempo...there's little need for over-distance running.
Edit: I may, in fact, be misinterpreting what you're saying regarding how the relative contribution of the aerobic system relates to actual training methodology.
Brian, that's about right. A friend made the comment last year, "Man, halfway through the second turn, you looked like you were hating life." Yep...that's about the only way to properly run a 400. That's the point where your body goes "Hey, wait a minute...just WTF do you think you're doing?"