400 training

do 400 meter runners( especially in high school) need to train in the 75-95%range or should they train below that range to get strength and then focus on speed, speed endurance and special endurance?

i didn’t realize people were so sensitive on this site. i’m talking about the beginning of the season, during the general prep period. do you do specifically low intensity work or do it combined with pure speed or speed endurance work. what should the ratio be? why read 400 posts when i can possibly get a specific answer.