A joint lock is a submission that wins a fight by forcing a joint — usually the elbow or shoulder — past the range of motion it can safely move through. The fighter on the receiving end has one choice: tap to submit before the joint gives out, or risk a torn ligament or a break. The armbar is the most common one you'll see, but it's part of a small family of arm locks that all work on the same basic principle.
The armbar: straightening the elbow past its limit
The armbar isolates one of the opponent's arms, traps it between the attacker's legs, and hyperextends the elbow — pushing it straight past the point where it naturally stops. It can be applied from several positions: off the back after taking an opponent down, from full guard on the ground, or even standing during a scramble.
The mechanics are simple even if the setup isn't: the attacker controls the wrist with both hands, pins the opponent's torso and shoulder with their legs so the arm can't bend or rotate away, and then extends their hips to straighten the elbow joint. Because the elbow only bends one way, there's very little room between "locked in" and "hyperextended," which is why armbars can finish a fight in seconds once fully secured — and why fighters tap the instant they feel it rather than testing it.
The kimura: twisting the shoulder
The kimura, sometimes called a double wristlock, attacks the shoulder instead of the elbow. The attacker bends the opponent's arm behind their back and rotates it — forcing internal rotation at the shoulder joint that the joint isn't built to handle at that angle. It's commonly attacked from side control, from guard, or out of a clinch against the fence.
Kimuras are often used as a control tool as much as a finishing one. Even when a fighter escapes the actual submission, being caught in a kimura grip pins them in a bad position and can set up a sweep, a takedown, or a transition to a more dangerous hold — which is part of why you'll see it attempted far more often than it actually finishes a fight.
The americana: the opposite twist
The americana (sometimes called a keylock) attacks the same shoulder joint as the kimura but rotates it the other way — forcing the opponent's own hand up toward their head rather than down toward their back. It's typically applied from a top pinning position like mount or side control, where the attacker has enough control to isolate the arm against the ground.
Because the americana needs that top-control setup, it shows up far more in grappling-heavy positions than in open scrambles, and it's less commonly seen finishing a fight at the highest levels of MMA than the armbar or kimura.
How to tell them apart while watching
| Lock | Joint attacked | Direction of force | Typical position |
|---|---|---|---|
| Armbar | Elbow | Straightens the arm past full extension | Guard, mount, back, or standing |
| Kimura | Shoulder | Rotates the arm behind the back | Side control, guard, clinch |
| Americana | Shoulder | Rotates the arm up toward the head | Mount, side control |
All three fall under the broader umbrella term "arm lock," which covers any submission attacking the arm rather than the neck (a category that includes chokes, which work completely differently — cutting off blood or air instead of attacking a joint).
Defending a joint lock
Fighters rarely defend a joint lock by simply muscling their arm free — by the time an armbar or kimura is fully locked in, the attacker has too much leverage for that to work. Instead, defense is mostly about preventing the lock from ever closing: keeping the elbow bent and tucked in tight (an armbar can't hyperextend an arm that's already folded against the body), fighting the grip before it's secured, or "stacking" the attacker — driving forward into them from inside their guard to take away the angle they need to finish.
Once a lock genuinely is deep, the safer move is almost always to tap rather than try to power out of it, which is exactly why referees treat a slap of the mat, the cage, or the opponent — or a clear verbal tap — as an instant, non-negotiable stop.
A related move: the wristlock
The armbar, kimura, and americana all attack the elbow or shoulder, but there's a smaller cousin that attacks the wrist itself — bending it past its normal range the same way an armbar bends the elbow. Wristlocks are legal in the UFC but rare, because they're easier to escape early and require an opponent to leave their wrist isolated in a way skilled grapplers usually avoid.
Why fighters tap instead of fighting through it
Unlike a choke, where a fighter can sometimes recover after a brief loss of consciousness with no lasting damage, a joint lock held past the tap risks a genuine structural injury — a hyperextended elbow, a torn labrum, a dislocated shoulder. Referees are watching for exactly this: a fighter's hand slapping the mat or cage floor, a verbal tap, or visible physical distress at the joint, any of which should end the fight immediately.
That's also why you'll see fighters roll, spin, or stack their opponent to escape a lock rather than simply pulling their arm free — a joint lock only works while the attacker maintains the exact angle and control that makes it effective, so breaking that angle is usually the only way out once it's deep.
The takeaway: every joint lock in MMA works the same way — isolate a joint, then move it somewhere it isn't built to go — and the differences between an armbar, a kimura, and an americana come down to which joint is attacked and which direction the force is applied. Once you know that, you can usually tell which submission is coming before the referee even has to react.