What's the Unbendable Arm and how can you use it
Updated: Feb 19, 2019
Here we have one of those mysteries of aikido. A mystery which many folk would say is extremely important to correct technique. “Unbendable arm”, is as common refrain from many teachers of aikido as “keep centre”.
Firstly the unbendable arm is most definitely not a muscular, rigidly held straight arm. It has a certain amount of give at the elbow and it remains "relaxed" yet extended and capable of withstanding considerable bending force.
It is probable that the unbendable arm is merely an example of the stretch reflex. This reflex is more often associated with the legs than the arm, but the same anatomical arrangements exist in the arms as well.
The stretch reflex keeps us standing without conscious thought or doing a huge amount of muscular activity. Our legs after all support all our weight yet they seem to do it without effort. This is achieved by a nervous pathway which senses any stretching of muscles fibres and causes a nerve to fire to contract the fibres (at the same time it causes fibres in the opposing muscle to relax). The pathway passes from the muscle, through the spinal cord and back into the muscle, so the brain is not involved and the response is very quick. As the control is exercised at the level of muscle fibres rather than the whole muscle it does not necessarily create any gross movement but it does mean that our muscle fibres are in a state of constant flux while maintaining posture but they are only doing enough work to maintain a steady state. As the brain is not involved we are not aware of any effort and as the muscle only does just enough to maintain stability we only tire gradually.
The important thing with the stretch reflex is that any conscious engagement of muscle will over-ride it. In other words it only works by consciously disengaging any physical intention apart from the desire that the arm should simply maintain its extension without effort. Any pushing or pulling immediately interrupts the stretch reflex and also creates an opposing reaction in our partner. The relaxed but extended unbendable arm is a key component of the higher levels of aikido. When combined with integrated movement from the centre it becomes very difficult to resist because the opponent cannot "read" any intention that would be telegraphed by the conscious use of muscular strength. Learning to just let the arm maintain extension while completing a technique means suspending the desire of the ego to force itself upon the opponent in an attempt to throw them to the ground.