The Clermont College Biology Department lists examples of flexor muscles as the biceps brachii and the hamstrings, and some examples of extensor muscles are the triceps brachii, the quadriceps femoris and the gastrocnemius. One of the most well-known extensor muscles is the Achilles tendon.
Muscles can only contract or pull and not push. Because of this, the Clermont College Biology Department explains that many of the body’s major muscles come in sets, known as antagonists, which perform opposite jobs. Flexor and extensor muscles are one example of such opposites. A flexor muscle bends a joint, whereas an extensor muscle straightens a joint.
For example, the muscle at the top and front of the arm, the biceps brachii, flexes or bends the arm at the elbow, whereas the muscle at the back of the arm, the triceps brachii, straightens it back out, extending it. Accordingly, the Clermont College Biology Department explains that the biceps brachii is the flexor muscle on the front of the arm, and the triceps brachii is the extensor muscle on the back of the arm.
The Clermont College Biology Department describes that the quadriceps femoris is the main extensor muscle on the front of the femur, whereas the hamstrings are the flexor muscles on the back of the thigh. Additionally, the biceps femoris is the outer hamstring muscle, and the semitendinosus is the inner hamstring muscle. The calf muscle, which is the gastrocnemius, is also an extensor muscle. It works together with the Achilles tendon to extend the foot.