One of the all time great exercise. Still a great way to prove a power to weight ratio in strength. The major muscles used here are the lats, biceps and Brachioradialis ( forearm).There are many different variations to do this exercise and different positions will change the emphasis on the muscles used. Shown here is the traditional wide grip chin up, this variation put the emphasis on the lats. The alternate photos are of the closed grip chin up. This put more emphasis on the biceps.