Originally Posted by TheCheese
Trying to brush up while extending results in lower acceleration that comes from the shoulder. If you brush across you are pulling your arm in by bending at the elbow and this generates much more acceleration.
No. you are not trying to extend but also not bending. the across comes from internal rotation of the humerus and forearm. the arm angle remains mainly constant.
I agree that you should not try to force a linear path but you should not try to swing across abruptly. just a natural circular path around the body.
here is the vid: