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).

# Muscles of flexion

## Upper limb
- of arm, at shoulder
Anterior compartment of the arm
Coracobrachialis
Biceps brachii
- Anterior compartment of the arm
Coracobrachialis
Biceps brachii
- 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
- Anterior compartment of the arm
Biceps brachii
Brachialis
Brachioradialis
- Biceps brachii
- Brachialis
- Brachioradialis
- Anterior compartment of the forearm
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Flexor digitorum superficialis
- 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
- Anterior compartment of the forearm
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Flexor digitorum superficialis
Flexor digitorum profundus
- 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)
- 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
- Flexor digitorum superficialis
- of distal phalanges, at distal interphalangeal joints
Flexor digitorum profundus
- Flexor digitorum profundus
- of thumb
Flexor pollicis longus
Flexor pollicis brevis
- 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)
- 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)
- Posterior compartment of thigh/Hamstrings
Biceps femoris
Semitendinosus
Semimembranosus
- 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
- Posterior compartment of leg
Flexor hallucis longus
Flexor digitorum longus
- 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
- Lumbrical muscle (foot)
- Plantar interossei
- Dorsal interossei

## Other
- torso/lumbar vertebrae
Rectus abdominis muscle
- Rectus abdominis muscle
- neck at atlanto-occipital joint
Longus capitis muscle
- Longus capitis muscle