This will be part of a series of shoulder mobility exercises.
As always, move within a range that does not cause pain.
Brachium is Latin for arm. Brachiation refers to swinging movement of the arm, usually pertaining to the way primates move from branch to branch.
Surfers in particular need to have good shoulder mobility. When I paddle laying down, (prone) the most tiring part is lifting my arm up for the next stroke.
Hours seated at keyboards, tend to make our shoulders round forwards, this is further compounded by tight hip flexors from sitting and driving.
Oh Yeah..Got to keep on moving....