Extensor muscles are a group of muscles responsible for extending or straightening a joint. They are primarily found in the arms and legs, allowing movements such as straightening the elbow or knee. When these muscles contract, they pull on the bones, increasing the angle between them. In the human body, extensor muscles are located on the posterior side of the limbs. For example, the triceps brachii is an extensor muscle in the arm that helps extend the elbow, while the quadriceps group in the thigh extends the knee. These muscles play a crucial role in various physical activities and movements.