Aim\ ① To study the numerical solution of established dynamic equations of the human upper extremity as simplified tworigidbody system for adduction/abduction motion.② To study the feasibility of calculating the muscular force through the motion parameters. Methods\ The Mathematica software is used

and literatures on motion parameters of human upper limb are referenced to solve the equations under the two conditions of knowing the motion parameters for evaluating the primary active forces and knowing the primary active forces for evaluating motion parameters. Results\ Through the calculations of the abovementioned two conditions

it is shown that the dynamic equations are determined.The parameters (Cardan angles)evaluating from knowing the primary active force are consistent with the given parameters. The singularity phenomenon is found in calculation of the second condtion. Conclusions\ The abovementioned dynamic equations can be solved in numerical method by Mathematica. It is feasible. To predict the muscular force by determining the motion parameters of human upper limb. For the singularity

a proper interval can be chosen in solving it.