Abstract
In Aikido, the use of a body motion called the &quto;unbendable arm&quto; has been proposed. We studied the difference between Ki (unbendable arm performance) and the muscle force in a flexing elbow joint from an electromyography (EMG) viewpoint. From our EMG study, we found that the EMG value of the triceps brachii muscle was significantly lower in the unbending arm, and the EMG value of the deltoid muscle was significantly higher in experienced subjects. This EMG change might explain the subjects' subjective observation that the "unbendable arm" was less difficult to resist than physical muscle force.
