The Joints

Something I talk to people about frequently is you only have to understand one limb to be successful in joint locks. In Brazilian Jiu Jitsu, you generally cannot attack fingers, toes, or the spine, so you are left with three breakable focuses.
Ball Joints- shoulders and hips
Hinge Joints- knees and elbows
Function Joints- wrists and ankles
Each joint has a partner in the four quadrants of the body and the attacks of one mimic the other. If you understand how to submit shoulders, elbows, and wrists, that can be translated to leg attacks. Having this information allows you to create more submission opportunities quickly, because you’re not rigidly seeking a perfect position. Focus on how the joints of one limb can be attacked and you can apply that to the other three.