Abstract
The problem of motor redundancy has been known as the Bernstein problem. This paper investigates the problem in motor control from the viewpoint of functional cooperativeness of muscles through a novel concept so called the “A-A ratio” and “A-A sum”. The former is defined as a normalized electromyogrphic (EMG) ratio of agonist-antagonist muscle pairs, whereas their nomalized EMG sum. We then apply a muscle synergy extraction method based on a physical model to EMG signals during human lower movements such as walking and running. The muscle synergy analysis specifies that muscle activities during these human lower movements can be described as a superposition of two muscle synergies invariant across subjects and across tasks. Furthermore we characterized the kinematic motor functions of the extracted muscle synergies. These findings indicate flexibility of muscle synergies across various tasks.
