It has been reported that the three pairs of antagonistic muscles including the mono- and bi-articular muscles in human limbs showed the perfectly coordinating activity pattern, and contributed to the output force control and force direction control at the wrist or ankle joint. This paper deals with a method of the functional evaluation of effective muscle strengths in the muscle coordinate system based on the functional role of the muscles contributing to the output force distribution. The output force distribution demonstrated a hexagonal shape, and the effective strengths of the functionally individual muscles could be calculated from the characteristics of this hexagonal shape. This will lead a human model into much more reality than the model operating in the conventional joint coordinate system.