BJJ Joint Lock Mechanics: How Armbars, Kimuras and Leglocks Work
BJJBJJ App Team·⏱️ 1 min read·🔄 Mar 31, 2026
☰Contents
Understand BJJ joint lock mechanics: how armbars, kimuras, heel hooks and shoulder locks apply force and why they cause tap-outs.
Understanding how joint locks apply force makes you better at finishing them and better at defending them. This guide explains the biomechanics of the major BJJ joint attacks.
Contents
Armlock Biomechanics
| Lock | Joint | Force Direction | Tap Indicator |
|---|---|---|---|
| Armbar | Elbow | Hyperextension | Elbow straightens, pressure felt |
| Kimura | Shoulder | External rotation | Shoulder twisting sensation |
| Americana | Shoulder | Internal rotation | Front shoulder pressure |
| Omoplata | Shoulder | Forward rotation | Top of shoulder pressure |
Leg Lock Biomechanics
- Straight ankle lock: Compression on the Achilles tendon and ankle extension. Predictable, lower injury risk.
- Kneebar: Hyperextension of the knee joint. Similar to armbar but on the knee.
- Heel hook: Rotational force on the knee ligaments (ACL/MCL). High injury risk — tap early.
When to Tap — The Mechanical Rule
- Tap when you feel the technique being applied correctly — before maximum force.
- For heel hooks: tap at first feeling of rotation — don't wait for pain.
- For armbars: tap before elbow locks fully — early tap prevents hyperextension injury.
Frequently Asked Questions
How does an armbar work?
An armbar hyperextends the elbow joint. The attacker uses their hips as a fulcrum, applying upward force to the wrist while the elbow is locked in place, forcing the joint past its natural range.
How does a kimura work?
The kimura is a shoulder lock using a figure-four grip. Rotating the forearm upward and behind the shoulder compresses and rotates the shoulder joint past its natural range of external rotation.
Why do heel hooks tap faster than ankle locks?
Heel hooks apply rotational force to the knee, targeting the ACL and MCL. The ligament damage happens before pain is felt — by the time you feel pain, damage may have already occurred. Ankle locks apply more predictable compression with earlier pain signals.