flexor

Flexor is a term used in anatomy to describe muscles or tendons that cause flexion, or bending, of a joint. The opposite group is extensor. The word derives from the Latin flectere, to bend. Flexors are organized into regional groups; in the upper limb, most flexors lie on the anterior (ventral) forearm and act to bend the wrist and fingers.

Prominent flexor muscles of the forearm include the flexor digitorum superficialis and profundus, flexor pollicis longus, flexor carpi radialis, and flexor carpi ulnaris. Their tendons pass through the carpal tunnel under the flexor retinaculum and are wrapped in tendon sheaths. In the digits, the flexor tendons bend the finger joints; the flexor pollicis longus bends the thumb. In the leg, the term is used for muscles such as flexor digitorum longus and flexor hallucis longus, which flex the toes and assist in plantarflexion and inversion.

Flexors work antagonistically with extensors to enable a range of motions. Clinically, flexor tendons are a common source of hand injury and may require surgical repair. Nerve or tendon pathology affecting flexors can impair grip and finger motion, while conditions such as carpal tunnel syndrome involve the nerve supply to many flexor muscles.