The One Arm Dumbbell Tricep Extension is an exercise that works the triceps brachii; the muscles of the back of the arm.
1. Stand up straight with your feet shoulder-width apart. Your one arm is stretched out slightly behind your head, holding a dumbbell, and is positioned close to your head.
2. Now, lower the dumbbell behind your head in a semicircular motion. Lower the dumbbell until your forearms touch your biceps.