arm locks Biomechanics: Joint locks

Kinesiology of the Armbar

The armbar, arguably the most iconic technique in grappling, is a submission that involves hyperextension of the elbow joint (humeroulnar joint). While there are two other joints around the elbow region:
1. humeroradial
2. radioulnar joint

After years of grappling many martial artists may lose a bit of range, but the average person should have about 5 degrees of hyperextension.


There are a variety of structures that limit hyperextension at the elbow:
1. Muscle: Elbow flexors, wrist flexors and forearm pronators are muscles at the elbow and forearm that help to support and resist excessive motion: These muscles include biceps brachii, brachialis, brachioradialis, flexor carpi radialis, flexor carpi ulnaris, palmaris longus and pronator teres.
2. Ligaments: The primary ligament to limit excessive extension is the ulnar or medial collateral ligament (not to be confused with the MCL in the knee), particularly the anterior fibers which are the strongest and thickest fibers of the ligament. The UCL is a fairly thick ligament and is highly innervated, meaning the mechanoreceptors within the structure help detect passive tension. This is why there is a relatively moderate amount of time from when the submission begins and when damage occurs compared to a leg attack.
3. The bony articulation of the humerus and the ulna. The trochlea of the humerus inserts into to the trochlear notch of the ulna and at end-range extension the moving bone has no more room to move.
4. The joint capsule is connective tissue that wraps around all three joints and is supported by ligamentous structures.

Humeroulnar hyperextension often leads to ligament strain or rupture, however if force is continued then dislocation of the ulna from the humerus can occur. While the muscles may become strained they are not likely to tear, more likely the muscle’s attachment on the ulna will rip off the main structure, which is referred to as an avulsion fracture.

How to use science to improve your armbar

Why do instructors often tell their students to keep the opponent’s thumb up when applying an armbar?
Controlling the position of the thumb is actually forearm rotation at the radioulnar joint. Thumb position dictates the alignment of the forearm bones: radius and ulna. When the forearm is turned palm up (supination) the radius sits next to the ulna and when the forearm is turned palm down (pronation) the two bones cross. However when in neutral (ie thumbs up) the radius sits on top of the ulna. This gives the attacker the proper leverage to cause dislocation. When the attacker’s hip generates a force in the superior direction you can maximally tension the UCL, and once the ligament fails you are in the ideal position to force the trochlea of humerus out of the trochlear notch of the ulna.

Dislocation and ligament damage can still occur, specifically if the palm is up (supinated), however this changes the submission slightly. Instead of causing a hyperextension you are imparting a valgus force, which is resisted by anterior and posterior fibers of the UCL.

How to use science to improve your armbar: Ideally when attacking with the armbar the line of force from your hips should be identical to the position of the thumb to elicit the fastest tap or cause maximum damage.

What are some long term consequences of not tapping to elbow locks?

Aside from acute injuries such as ligament sprains, muscle strains or possible dislocation there are also long term damages that can occur if you continually tap late. Repetitive microtrauma of continued stress may cause formation of loose fragments of bone or cartilage to form along the elbow joint.

Why does this matter? The arthrokinematics of the humeroulnar joint for elbow extension requires the olecranon process to fit into the olecranon fossa. If there are ectopic formations or bone spurs that form inside the fossa then full extension will be limited.

Conservative treatment may help to regain the loss of motion, but often this requires surgical intervention. The best intervention is prevention.

Take care of your body so you don’t develop impairments that will interfere with your jiu jitsu.

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