Stand upright with one hand behind your back and the other hand gripping the handle at shoulder-width with an underhand grip in front of your shoulder.
Exhale and extend your arm while keeping your upper arm in place.
Continue until your arm is straight.
Inhale and allow your arm to raise, returning it to the starting position.
After all reps are completed, switch sides and repeat the movement. 10 reps prescribed means you should perform 10 reps on each side (20 total).