An Estimation Method of Muscle Force by using Variable Moment Arm Vector

This paper presents an estimation method of muscle force which is considered variation of muscle force direction. We define a moment arm vector of muscle in musculoskeletal model. Its direction represents a rotational axis of the joint torque which is generated by contraction of the muscle. The direction of moment arm vector is redefined repeatedly according to joint torque calculated by inverse dynamical analysis. Muscle forces are estimated by optimization with the modified moment arm vector being employed in constraint condition which represents equilibrium between muscle forces and joint torques. We applied this method to analyzing braking motion. Resultant patterns of muscle forces match measured electromyogram. Consequently, it is verified that the variation of muscle force direction is necessary to estimate muscle force accurately.