If you're looking to work your triceps in particular, you'll find skull crushers are a good way to do it. This exercise uses gravity to specifically work this area, so start by learning the basic technique. You can switch things up a bit to work your lateral or long head muscle in your triceps. Are you ready to make your tricep workout even better? Look no further than the well-known exercise called skull crushers . Skull crushers , also known as lying triceps extensions, are isolation exercises that work the triceps brachii muscle. Learn how to do skull crushers (also called lying triceps extensions ) with perfect form in order to build strong triceps. Plus, find out the common skull crusher form mistakes, the exercise's main benefits, and modifications and progressions to try. The dumbbell skull crusher exercise (or the Triceps Extension) is a tried-and-true triceps exercise intended to develop that horseshoe-shaped muscle on the back of the arm.