So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. ... For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor.
Muscles move the body by contracting against the skeleton. When muscles contract, they get shorter. By contracting, muscles pull on bones and allow the body to move. For example, the biceps and triceps muscles work together to allow you to bend and straighten your elbow.
