Forearm Extensors

arms

The forearm extensors are the muscles on the back of your forearm that straighten your fingers and bend your wrist backward. Their main job during lifting is holding the wrist steady so your grip can work.

Forearm Extensors highlighted on an anatomical figure, from behind.
Where it sits, from behind.

This is the muscle mass on the top of the forearm — the side you see when your palm faces down. Grouped here are the two radial wrist extensors, the extensor of the fingers, the extensor of the little finger, the ulnar wrist extensor, and anconeus. Most of them start from a shared tendon on the bump on the outer side of the elbow and run down to the back of the hand.

Their obvious job is opening the hand and bending the wrist backward. Their more important job during lifting is less visible: when you grip something hard, the finger flexors would pull your wrist into flexion if nothing resisted them, so the extensors contract to hold the wrist straight. Almost all of their work under a heavy bar is that, not movement.

They are considerably weaker than the flexors on the other side, and this is normal rather than an imbalance — the hand is built to close harder than it opens. What is not normal is the ratio that develops from training only one side, since pulling, carrying and gripping all load the flexors and nothing in a typical program loads the extensors on purpose.

One member of this grouping does not belong to the forearm at all. Anconeus is a small triangular muscle at the elbow that assists elbow extension and stabilises the joint during forearm rotation; it is included because of where it sits, not because it extends the wrist.

Training notes

This is the side of the forearm worth training directly, precisely because nothing else trains it. Reverse wrist curls and reverse curls are the direct movements, and both work at weights that will look small.

Reverse curls are the more efficient choice because they load the wrist extensors isometrically while training the brachioradialis and brachialis through a range. One movement covering three useful things is a better use of a slot than a dedicated wrist exercise.

Their function during heavy pulling is isometric — holding the wrist straight — so training them with holds and with controlled reverse curls suits the job better than fast repetitions.

Grip work benefits indirectly. A wrist that collapses into flexion under load reduces the length available to the finger flexors, so extensor strength contributes to holding on even though it contributes nothing to closing the hand.

Anatomy

Origin
  • A common extensor tendon on the lateral epicondyle of the humerus, shared by most of this grouping
  • Extensor carpi radialis longus arises higher, from the lower third of the lateral supracondylar ridge
  • Extensor carpi ulnaris takes a second head from the posterior border of the ulna; anconeus arises from the lateral epicondyle independently
Insertion
  • A range rather than one point: the base of the second metacarpal (extensor carpi radialis longus), the base of the third metacarpal (extensor carpi radialis brevis), the base of the fifth metacarpal (extensor carpi ulnaris), and the extensor hoods of the digits (extensor digitorum, extensor digiti minimi)
  • Anconeus is the exception and does not reach the wrist — it inserts on the olecranon and the upper posterior surface of the ulna
Actions
  • Extend the wrist
  • Extend the fingers at the knuckles
  • Deviate the hand toward the thumb or the little finger side
  • Stabilise the wrist against the pull of the finger flexors during gripping
  • Assist elbow extension and stabilise the elbow during forearm rotation (anconeus)
Innervation
Radial nerve and its deep posterior interosseous branch (C6–C8)

This page covers extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris and anconeus. As with the flexor grouping it is a convenience rather than an anatomical entity, and no reference uses the name.

Origin and insertion are therefore stated as ranges. The origin is largely shared — the common extensor tendon on the lateral epicondyle — with two documented departures: extensor carpi radialis longus arises above it on the supracondylar ridge, and extensor carpi ulnaris takes an additional ulnar head. The insertions span the bases of the metacarpals and the extensor hoods of the fingers.

Anconeus is the odd inclusion and is worth naming explicitly. It is an elbow muscle, not a wrist muscle: it assists triceps in extending the elbow and stabilises the joint during pronation and supination. It is grouped here because it sits immediately alongside the extensor mass, rather than because it shares their function.

The deep extensor layer — the three muscles of the thumb and extensor indicis — and supinator are not included. Innervation of the whole compartment is radial, with the deeper muscles supplied by the posterior interosseous branch.

Under load

Direct loading is by wrist extension and by gripping in a pronated position, where the extensors work isometrically against the flexors.

The compartment is under far less incidental load than the flexor compartment, since ordinary use and most training involve closing the hand rather than opening it.

Anconeus is loaded by elbow extension rather than by anything done at the wrist, so the grouping's exercises do not train all of its members equally.

Exercises

Antagonists

Synergists