This paper proposes methodologies for analyzing the motions of a human arm during specific work activities. First, a musculoskeletal model of a human upper limb is constructed. Next, assuming that a muscle consists of a contractile element and an elastic element, the energy consumed by the muscles is formulated as a function of the muscular forces and the contraction velocities of the muscles. Then, the muscular force sharing is predicted by solving an optimization problemin which the summation of the energy consumed in all of the muscles of the upperlimb model is minimized. Finally, the optimal motion of a human body is defined as that where energy consumed in the muscles during working processes is minimized. Then a method to determine the optimal motion of the upper limb model is presented for fundamental work activities.