This exercise is used to build strength in the tricep while getting a good stretch at the bottom of the movement.
Begin by bringing a dumbbell up to shoulder height and then extended over your head. Your palm should be facing forward with your pinkie facing the ceiling, and your other hand should be at your side or holding onto a fixed object. Slowly lower the dumbbell by bending at your elbow and keeping your upper arm in place. Continue to lower the dumbbell until it is behind your head; hold this position to fully stretch the tricep. Then, contract your tricep and push the dumbbell back to the starting position. Repeat until you have completed the amount of repetitions in your set, then switch arms and do it again.
Start with your weaker arm so you know that you will not do more repetitions with one arm than the other. This ensures that you will be able to work each arm the same and build the weaker arm.