Using vicon bodybuilder and plug-in-gait to generate L5/S1 angles, forces and moments

Currently the most widely used and accepted Vicon model is the Plug-in-Gait (PIG). Unfortunately, the PIG output value for the lumbar section only provides the angle difference between the thorax and the pelvis. Because the PIG is so widely used by advanced biomechanical analysts for defining body segment kinematics for aerospace and other industries, it would be a great advantage to be able to enhance the fidelity of the PIG model outputs by attaching body regions, such as spinal sections. Thus, the work explained in this paper describes how a virtual lumbar segment which generates model angle output values for the L5/S1 can be easily added to the PIG body segment definition, using the BodyBuilder (BB) for Biomechanics programming language. The methodology described in this paper utilizes the original PIG marker set and does not require any additional markers. Furthermore, the same method and model can provide L5/S1 forces and moments.