Extension (kinesiology)

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File:Human anatomy planes.svg

Anatomical planes in a human. Extension usually occurs in the sagittal plane when the body is in the anatomical position

File:LegExtensionMachineExercise.JPG

The leg extension is an isolation exercise.

In kinesiology, extension is a movement of a joint that results in increased angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed (bent) elbow. Straightening of the arm would require extension at the elbow joint. If the head is tilted all the way back, the neck is said to be extended.

In some anatomical muscle names, particularly with muscles of the forearm and the Cnemis, the term occurs explicitly as the second word in the Latin spelling of the name (for example, Musculus extensor carpi ulnaris).

While extension is a movement, the terms "extend" versus "flexed" refer to the final position of a body part with reference to the anatomical position of the body. For example, if an arm fully bent at the elbow is slightly extended, it will still be called "flexed" or "semiflexed", and will be called "extended" only upon complete straightening of the arm.

The movement in the opposite directions is called flexion. Flexion decreases the angle between the bones of the limb at a joint, while extension increases it.

With the foot, extension is usually called plantarflexion.

Hyperextension

If a part of the body such as a joint is overstretched or "bent backwards" because of exaggerated extension motion, then one speaks of a hyperextension (as with the knee). This puts a lot of stress on the ligaments of the joint, and need not always be a voluntary movement, but may occur as part of accidents, falls, or other causes of trauma.

Hyperextension is also sometimes defined as normal movement into the space posterior to the anatomical position.

Muscles of extension

Upper limb

• of arm at shoulder
  • Axilla and Shoulder
    • Latissimus Dorsi
    • Posterior Fibres of Deltoid
    • Teres Major

• of forearm at elbow
  • Posterior compartment of the arm
    • Triceps
    • Anconeus

• of hand at wrist
  • Posterior compartment of the forearm
    • Extensor carpi radialis longus
    • Extensor carpi radialis brevis
    • Extensor carpi ulnaris
    • Extensor digitorum

• of phalanges, at all joints
  • Posterior compartment of the forearm
    • Extensor digitorum
    • Extensor digiti minimi (little finger only)
    • Extensor indicis (index finger only)

• of phalanges, at interphalangeal joints
  • Lumbricals of the hand
  • Dorsal interossei of the hand
  • Palmar interossei

• of thumb
  • Extensor pollicis brevis (proximal phalange)
  • Extensor pollicis longus (distal phalange)

Lower limb

• of thigh/femur at hip
  • Gluteus maximus
  • Posterior compartment of thigh
    • Biceps femoris
    • Semitendinosus
    • Semimembranosus

• of leg at knee (L3-L4)
  • Quadriceps
    • Rectus femoris muscle
    • Vastus medialis
    • Vastus lateralis
    • Vastus intermedius

• of toes
  • Extensor hallucis longus
  • Extensor digitorum longus
  • Extensor digitorum brevis
  • Extensor hallucis brevis

Back

• Extensor spinae
• Range of motion

External links

• Dictionary at eMedicine Extension