Lean on the bench with your leg and a fully extended arm while holding a dumbbell in your other arm underneath your shoulder with an inward facing grip.
Exhale and drive your elbow backward, keeping your torso and other arm from moving.
Continue driving your elbow backward to lift the dumbbell until your elbow passes your torso.
Inhale and lower the dumbbell, straightening out your arm to return 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).