Interesting post. Speed doesn't seem to be the issue. I coach an 800m runner with a 400m pb of 51.05. In order to build more aerobic strength I world recommend 400's at 3k pace, threshold running, and hills. At this time of the year our fast stuff is in the shape of 150 accelerations. Hill reps range between 60m-300m. Our lactate tolerance sessions are hills at this time of the year w/nationals in late March. I had a 17 year old come to me in May and off this training he has already run 1:53 and 3:56 for 800/1500 he runs about 30 miles per week.
So it's more of a strength thing? What exactly does strength mean in terms of running the 800? I know theres speed, endurance, and strength but I'm not too sure on what strength is.