Triceps make up 2/3 of your arm mass. In addition to filling out shirt sleeves, they're also important for locking out big ol' benches.  You'll want to make sure your triceps get their due punishment in the gym, and these overhead extensions with a rope are a great way to do it. In the video, Justin Harris knocks out a huge set of extensions. To do this exercise, get into a split stance with the weight extended in front of you and begin the extensions. Be sure you keep your back straight and maintain a good torso angle, as Justin does.