Flexion

Flexion is a term used in both anatomy and linguistics to describe bending or inflection, respectively. In anatomy, flexion refers to a movement that decreases the angle between two adjacent body parts, typically in the sagittal plane. It contrasts with extension, which increases that angle. Flexion is produced by flexor muscles and antagonized by extensor muscles. Common examples include elbow flexion (bringing the forearm toward the upper arm), knee flexion (bending the leg), and wrist flexion (bending the hand toward the forearm). At the ankle, plantar flexion and dorsiflexion are specialized movements that adjust the angle between the foot and leg. Clinically, the range of flexion is assessed to evaluate joint mobility; restrictions or excessive flexion can reflect injury, arthritis, or postoperative stiffness and may be addressed with rehabilitation.

In linguistics, flexion denotes inflectional changes to a word to express grammatical categories such as tense, number, case, mood, or person. This process alters a word’s form without creating a new lexical item. Examples include English verbs adding -s for third-person singular (she walks) or -ed for past tense (walked), and pronoun case changes (he vs him). Some languages exhibit more extensive inflection, with nouns, adjectives, and verbs carrying multiple endings or internal vowel changes to signal their grammatical role.

Etymology traces both senses to the Latin flexio, meaning bending. In everyday use, flexion commonly refers to joint bending, while in linguistic contexts it refers to the systematic modification of word forms to convey grammatical meaning.