There are a few key muscles in the chest that are responsible for its strength and function. The pectoralis major is the largest muscle in the chest and is responsible for pulling the arm down and across the body. The pectoralis minor is a small, triangular muscle that lies underneath the pectoralis major and helps to raise the shoulder up and forward. The serratus anterior is a long, thin muscle that runs along the side of the chest and helps to stabilize the shoulder blade.
