Ok, I'm a 400/800 runner who can go 49.XX and 1:57 at the moment. I feel that I'm approaching the limit of how fast I can run the 800 on pure speed ( splits are usually (55-1:25). I'm more than willing to put in the work to run 30-40 mpw but it just seems my bodies not meant for it. I ran XC and barely finished a 21:00 5k. I try every so often to go on long runs with the distance runner but I always get left because they go 7:00 pace for 8 and I blow up terribly if I go faster than 8:00 pace for 5. Should I just fight through it and get the must needed endurance or continue to train as a sprinter.