Cable One Arm Tricep Extension

Muscles worked

Filled = primary · Outlined = secondary

Source: Free Exercise DB (public domain)

With your right hand, grasp a single handle attached to the high-cable pulley using a supinated (underhand; palms facing up) grip. You should be standing directly in front of the weight stack.
Now pull the handle down so that your upper arm and elbow are locked in to the side of your body. Your upper arm and forearm should form an acute angle (less than 90-degrees). You can keep the other arm by the waist and you can have one leg in front of you and the other one back for better balance. This will be your starting position.
As you contract the triceps, move the single handle attachment down to your side until your arm is straight. Breathe out as you perform this movement. Tip: Only the forearms should move. Your upper arms should remain stationary at all times.
Squeeze the triceps and hold for a second in this contracted position.
Slowly return the handle to the starting position.
Repeat for the recommended amount of repetitions and then perform the same movement with the other arm.