The biceps are classified as skeletal muscles because they attach directly to the skeleton. According to Healthy Living, they are attached to the skeleton by tendons and are controlled voluntarily. As explained by education.com, skeletal muscles generally work in pairs; one muscle works in combination with an antagonistic muscle to move a joint such as the elbow or knee.
According to the BBC, antagonistic muscles work in pairs to allow the bone to move back and forth to its original position. For example, as the biceps muscle contracts, the triceps muscle relaxes or stretches out and the arm moves up. When the reverse happens, with the triceps contracting and the biceps relaxing, the arm moves down.
The BBC explains that there are three types of muscles in the body: skeletal, cardiac and smooth. Skeletal muscles cause diverse movements of the skeleton and can be controlled voluntarily. Cardiac muscle is only located in walls of the heart and is controlled involuntary. Smooth muscle is found in hollow organs and blood vessels and is also controlled involuntary. According to the Worlds of David Darling, a muscle may work as a prime mover, antagonist, fixator or synergist. Any muscle that opposes the movement of a prime mover is classified as an antagonist. Fixators contract to stabilize the origin of the prime mover, and synergists serve to contract and stabilize the intermediate joints.