what role do arms play at top speed???
if they control things during acceleration, than what do they do at top speed??
I´m not an expert , but I understand that arms should not be so tense during top speed phase so the better thing to do is just perfome a correct motion in a relaxed manner not forcing their action.
For what I´ve observed in myself,when I pump my arms during top speed phase trying to make the correct motion in a forced manner (with powerful pumping action) what I´ve finally got is be more slow 
and loose energy more easily.
Well I hope it could help , but remenber that I´m not an expert lol 
Maintainance of form and leg speed.
so the focus changes from arms, to the legs???
To be honest with you im a “Do” runner. Some things just happen and I can’t professionally explain what are the roles, purpose etc. I can only give you common sense answers. The role of the arms at top speed? To maintain your form and leg cadence.
well this might not be the answer to your question, but if you didn’t use your arms, imagine what would happen!
I guess their role is to balance out the leg action and keep you from turning side to side… i’m sure someone will come along and give the real answer soon enough
Once again…
ARM ACTION
The arms CAN control the legs when things are going right but they CAN’T help when mechanics go south (pushing out the back) With good arm action the “pull” is down not back, just as the action is with the legs. A constant angle is seldom maintained with the arms usually moving from around 85degrees in front to about 95 to 100degrees on the back-swing, which is within the acceptable range (arms too close to the torso in front may limit hip rotation and too open in the back may change the center of balance, delay the return, and diminish the elastic response around the shoulder) . It shouldn’t take a lot of arm strength to maintain the proper arm angles or even the rate. The main contribution of upper body strength is to the general strength of the entire organism. The hand comes up to face level in front, and you pull down from there.
The arms will come towards the mid line (but not cross it) with good mechanics, as this initiates the shoulder rotation required to compensate for the counter-rotation of the hip. The mechanics must be checked on two planes- front and side to see what’s really going on.
An incomplete arm action must limit hip rotation by failing to provide sufficient counter-rotation.
The arms can be held at 90 degrees but as speed goes up the forces at work do the opening up without any conscious input. (At a lower velocity, it works as you see with Tommy above, but at the new 100 m velocities, there are greater forces at work) If you deliberately “break” at the elbow, you’ll loose the elastic rebound around the shoulder joint which facilitates the return, and dissipate energy from the upper arm action.
If the angle gets too small in front, it prevents full rotation at the hips by limiting compensatory rotation at the shoulder, moves the CG back slightly, forcing forward movement at the shoulders, interfering with force delivery (extension) through the hip and interfering with the natural rebound/return action of the arm at the shoulder at the completion of the back-swing, and so on and so on… (CF)
Thanks to TheOne!
ok, so the focus is on the arms for the whole race, or just the acceleration phase 0-30m???
Whole Race I guess, at least thats what I do.
what I have noticed is that if I due my sprinters to drive the hands down within the last 5 meters (100m) they don’t deacellerate as much; matter of fact it pushes them into a lean much more easily.