The biceps brachaii is a muscle in the upper arm spanning from the shoulder down to the elbow. It’s called the biceps because it is split into two muscle bellies at the upper end that attach in two separate places in the shoulder. It has only one attachment at the elbow. The biceps are primarily responsible for bending the elbow, for example, bringing your fists to your mouth, and supinating the forearm, such as turning a screwdriver. There’s another muscle under the biceps called the brachialis, which provides even more strength bending the elbow.