The arm muscle term ARM MUSCLE consists of four parts: TRICEPS (7 letters), BICEP (5 letters), BICEPS (6 letters), and LAT (3 letters). The triceps is a large three-headed muscle located at the back of the upper arm. It is responsible for extending the elbow joint. The bicep is a two-headed muscle located at the front of the upper arm. It is responsible for flexing the elbow joint. The BICEPS is a two-headed muscle located at the front of the upper arm. It is responsible for flexing the shoulder joint. The latissimus dorsi, or LAT, is a large, flat muscle located on the back. It is responsible for adduction and extension of the shoulder joint.