This is an excerpt from Jim Stoppani's Encyclopedia of Muscle & Strength-3rd Edition by Jim Stoppani.
With a slight bend in your knees, stand facing a high-pulley cable with a rope attached to it. Your feet should be about shoulder-width apart. Grasp the ends of the rope near the rubber stoppers with an overhand grip and hold the rope at chest level with your elbows tight against your sides. Pull your shoulder blades back and down and stick your chest out and up.
Keeping your elbows stationary, straighten your arms until they are fully extended. As you do so, spread the ends of the rope apart for a greater contraction. Pause at full arm extension and flex your triceps, then slowly return the bar to the starting position.
Quick Tip At the bottom of the rep, focus on pronating the forearms so the palms face back, pressing down with the thumbs, instead of keeping the forearms in a neutral position (palms facing in). This will better target the lateral head of the triceps.
Modifications and Variations
This exercise can also be done one arm at a time (one-arm rope triceps pressdown) by grabbing both sides of the rope in one hand.