One of the fundamental concepts we use in aikido is the “unbendable arm”. This is used in other martial arts as well, such as tai chi. The unbendable arm can be a difficult concept to grasp at first, but it is a very important one.
To demonstrate unbendable arm, let your arms hang naturally at your sides. Now bring them straight up to your center line in front of you. Your arm should be outstretched with a slight bend in the elbow. You do NOT want to lock or collapse the elbow.
Unbendable arm can be used for balance breaks, releases, and many other aikido techniques. It is one of the fundamental building blocks of the art. This video demonstrates the concept of unbendable arm.