So how would you cue what the arms should do, to a young athlete? Like I have said, I work with young athletes and I would think the reason people cue with 90 degrees is because it is the easiest way(that i know of)to explain to a younger athlete how to run with proper form within their own abilities. They dont have enough control of their limbs to be able to "open and close throughout" without really messing up their running form. So to prevent that from happening, you make an arbitrary number that a lot of people can relate to and understand and have them stick to that and learn how to control their arms. Later on in training once they have full control of their body, through having them cognitively think about where their arms should be, you can start to have them advance. I understand that in elite athletes you can have them run like but do you think it is bad to teach a young athlete to start that his arms to be at 'about' 90 degrees.
I know its ELITEtrack.com but not everyone here trains just the elite.