STARTING POSITION:
Select the appropriate resistance in the weight stack. Put a bench in front of the pulley. There should be a cable bar that is attached to a high pulley. Grab it and kneel on the floor between the bench and the pulley. You should use a prone grip. Place the elbows on the bench, the head between your shoulders and the elbows fully bent. Contract your pelvic floor and core while keeping your chest up.
MOVEMENT:
Contracting your triceps, fully extend your elbows while you exhale. Make sure you only move the forearms. Return to the starting position in a smooth movement while you inhale. The moving weights should not touch the rest of the stack.
TIPS: The exercise key is quality over quantity. The trick is to perform the exercise using proper form.