Flexion

Overview
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal (bones, cartilage, and ligaments) and muscular (muscles and tendons) systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder. The trunk may be flexed toward the legs or the neck to the chest.

The opposite term is extension, or straightening. Flexion decreases the angle between the bones of the limb at a joint, and extension increases it.

Note that specific flexion activities may occur only along the sagittal plane, i.e. from the forward to backward direction, and not side-to-side direction, which is further discussed in abduction.

Exercises
Active range of motion exercises include movements such as flexion and extension. These exercises are used after an injury or surgery. They are done by a physical therapist or nurse initially, and may be continued by the patient.

In the healing process, active range of motion exercises, should avoid forcing the appendage into the extension or flexion position. The stress induced may re-injure the affected appendage (limb).

Upper limb

 * of arm, at shoulder
 * Anterior compartment of the arm
 * Coracobrachialis
 * Biceps brachii


 * of forearm, at elbow
 * Anterior compartment of the arm
 * Biceps brachii
 * Brachialis
 * Brachioradialis
 * Anterior compartment of the forearm
 * Pronator teres
 * Flexor carpi radialis
 * Palmaris longus
 * Flexor carpi ulnaris
 * Flexor digitorum superficialis


 * of hand, at wrist
 * Anterior compartment of the forearm
 * Flexor carpi radialis
 * Palmaris longus
 * Flexor carpi ulnaris
 * Flexor digitorum superficialis
 * Flexor digitorum profundus


 * of proximal phalanges, at metacarpophalangeal joint
 * Lumbricals of the hand
 * Dorsal interossei of the hand
 * Palmar interossei
 * Flexor digiti minimi brevis (little finger only)


 * of intermediate phalanges, at proximal interphalangeal joints
 * Flexor digitorum superficialis


 * of distal phalanges, at distal interphalangeal joints
 * Flexor digitorum profundus


 * of thumb
 * Flexor pollicis longus
 * Flexor pollicis brevis

Lower limb

 * of femur/thigh at hip (L1-L2)
 * Iliopsoas
 * Tensor fasciae latae
 * Rectus femoris
 * (additional minor contributions from other hip flexors)


 * of leg at knee (L5-S2)
 * Posterior compartment of thigh/Hamstrings
 * Biceps femoris
 * Semitendinosus
 * Semimembranosus
 * Gracilis
 * Sartorius
 * Tensor fasciae latae
 * Gastrocnemius
 * Popliteus
 * Plantaris (negligible)


 * of toes
 * Posterior compartment of leg
 * Flexor hallucis longus
 * Flexor digitorum longus
 * Flexor digitorum brevis
 * Quadratus plantae
 * Flexor hallucis brevis
 * Flexor digiti minimi brevis


 * of proximal phalanges at metatarsophalangeal joint
 * Lumbrical muscle (foot)
 * Plantar interossei
 * Dorsal interossei

Other

 * torso/lumbar vertebrae
 * Rectus abdominis muscle


 * neck at atlanto-occipital joint
 * Longus capitis muscle