The cable tricep extension—also known as the cable rope triceps pushdown—is an effective triceps exercise. The triceps extension is an exercise you can do with a weight machine to work the muscle in the back of the upper arm. As the name implies, the triceps extension targets the triceps muscle, located here in the back of the upper arm. Properly done, the triceps extension helps strengthen and tone the back of your upper arm. If you use a cable system, you can also work your core muscles and improve your stability.