Good functional arms are not flat and straight. The hands should always be in front of the body and the elbows should be slightly flexed. This would resemble a hug pose.
To improve the coordination between shoulder, arm and hand, start by positioning the brush on the base of your skull, on the occiptal bone. Use the opposite hand of the side you are brushing. Keep your head aligned as much as possible, this should require a small pressure of the head against the brush.
Brush down the path of Upper Trapezium muscle, behind the shoulder over the posterior deltoid muscle, then follow down the triceps muscle.
Always give heed to the coaptation of the should in it’s socket, by utilizing your muscles to keep a good positioning.
Continue down the hairless part of your forearm until you reach the palm of the hand. Keep the hand spherical and the fingers long. Keep the hand aligned with the middle line of your body, around your navel.
Start the brushing on the thumb area, following the hairy part of your arm, up the biceps muscle all the way up to your clavicle. On the pectorals brush in the shape of a horizontal figure of 8 (infinite), adding width to the shoulders.
From the collarbone and sternum brush up your ECM towards the mastoid process on the base of your skull, behind your ear.
Repeat the action a few times. Remember the objective is to comb the muscular fibers, hence the brush strokes being strong and precise.
Compare both sides before you brush the other side.