I. Introduction
Extensive experimental studies have been carried out to identify biological control strategies of human arms and hands. Humans can perform a variety of dexterous movements by adjusting dynamic characteristics of the musculoskeletal system in motion. For example, a volleyball player can serve an extraordinarily fast ball through controlling his arm dynamics and creating an arc-shaped movement of his arm. The momentum of the ball depends not only on the strong muscle power of the player, but also on the ability to freely control his arm dynamics and learned skills. Much research has been done on human movements and often described with mechanical impedance parameters; stiffness, viscosity, and inertia [1] [2]. Gomi et al. [3] and Tsuji et al. [4] included arm movement and examined human hand characteristics, including inertia, viscosity and stiffness in multi-joint arm movements.