Now for wrist flex (think wrist curl up) -
flexes
Neutral position:
Extended:
Now forearm rotation (think turning a door knob) -
pronates
Neutral
Extended
Do this with both palm up and palm down. Also you can invert the guitar (body up) to work the biceps brachi. Again 3 sets of 8-10 reps to failure. Choke up or down to change load.
Hugh