Aerobic v Anaerobic work
Study that i read was 54% aerobic/ 46% anaerobic
you get 12 seconds of "free" anaerobic from the energy stored in a rested state in your muscles, so you might as well get out hard and not waste it.
in my experience, the race is aerobic from then until about 250m to go....you have to train to feel "comfortable" even at face pace so that you can reacts to the two kicks that occur in every elit 800m race.
250m to go or so the pace changes usually be someone forcing the issue and you have to react in one to two strides, you start to feel the burn but your strength work lets you power through and keep your basic stride.
With 120 to go the race begins, either you are there or you are off the pace, but at this point it is completely anaerobic and you are flat out...most runners will shift and sit like a sprinter and see if they have more energy in the muscles, but at this point you have 15 seconds or so until the monkey is on your back and you rig up. So dont start the flat out too early!
I agree that the anaerobic system is much more endocrine related (ie enzymatic) and you can tune it up in 6-8 weeks...you also get stale REALLY fast once you are peeking (4 weeks and it is tough to keep super sharp).
Aerobic work is more physiological, capillary development, cellular, oxygen transport, etc..improve your power/body weight ratio so that you are increasing "horsepower". At the end of the day you have the motor (legs) moving the luggage (upper body). You can REALLY keep improving this at least into your late 20s if you train consistantly and stay healthy on your feet.
Peter Coe also address improving power for stride length with hills/circuits, and as we discussed before nervous system by running slight downhills fast with turnover. in the 800m a 1 percent improvement is 1 second, so you might make a 1:43 guy run 1:41 this way, and Coe certainty did.
Also, ALOT easier if you are working with someone with an enormous amount of natural talent. In the running group I worked out with our High School times were 1:51 (me), 1:50, 1:49, and 1:48.