Figure 3.

Base compliance alters the measured force in the over constrained case. The scale bar for force is 0.3 N in all directions and for moments 0.01 N-m in all directions. A balanced transducer compliance is used throughout this figure (diagonal terms of S_t are 10⁷). Column 1 shows generalized forces measured with matched force constraints and joint dofs. Column 2 shows forces from the overconstrained case. Row A shows results from the inverse and pseudoinverse. This is identical to Row A in Fig. 2. Row B depicts forces using a high base stiffness. As the base becomes less stiff larger force and torques are measured. See B, C, and D. Row E shows the force and moment calculated with the femur removed, that is, the tibia is assumed to be attached to the force transducer but there is no reaction force from the femur at the knee. Force from the muscle is pulling directly on the tibia. Note that column 2, D and E, are identical—if the base becomes compliant enough the tibia is completely constrained by the force transducer—no force is transmitted through the femur.