Flexor carpi ulnaris
The wrist flexor on the little-finger side, and the strongest of them.
- Type
- Muscle
- Region
- Forearm
- Standard name
- m. flexor carpi ulnaris
- Origin
- Medial epicondyle of the humerus and the olecranon and posterior border of the ulna
- Insertion
- Pisiform, hook of the hamate, and the base of the fifth metacarpal
- Actions
- wrist flexionwrist ulnar deviation
- Verify
- TA2 2483 TA98 A04.6.02.030
What it is
The most medial of the superficial forearm flexors, running from the inner elbow and the ulna down to the little-finger side of the wrist. Its tendon is easily felt on the front of the wrist, nearest the little finger.
It attaches to the pisiform, a small pea-shaped sesamoid bone in the wrist, and continues from there to the hamate and the fifth metacarpal.
The ulnar nerve passes between its two heads of origin at the elbow and then runs alongside it down the forearm — which is why the muscle appears constantly in discussions of ulnar nerve problems.
What it does
Flexes the wrist and deviates it towards the little finger. It is generally the strongest of the wrist flexors.
What loads it
Gripping, wrist curls, and any load carried in the hand. Movements deviating the wrist towards the little finger against resistance, such as swinging a hammer or a racquet.
What is commonly got wrong about it
"Funny bone" as a bone. The sensation comes from striking the ulnar nerve where it passes behind the inner elbow, immediately before it dives between this muscle's two heads. It is a nerve, not a bone, and not this muscle.
Cubital tunnel problems as an elbow joint problem. Compression of the ulnar nerve at the elbow produces numbness in the ring and little fingers. It is a nerve issue and it needs assessment — persistent numbness in a hand is not a training question.
That the wrist flexors need heavy dedicated work. They are loaded in every carry, every deadlift and every pull-up. Dedicated work is optional rather than foundational.