The human body can be modeled as a linked-segment system. Here, each segment is regarded as a rigid body and the segments are linked to each other at the joints. But if the focus of the analysis is on the whole body CM kinematics, it is no different from a system of particles. In other words, depending on the analysis focus, one may view the human body in different ways.
In many motion analysis systems body modeling is just a pre-step of the marker digitizing or tracking. Although a body model in these systems contain the inertial properties (body segment parameters; BSPs) of the segments, they are often very limited. The typical BSP data allowed in the model are the BSP ratios such as the mass ratios, CM location ratios, and the ROG (radius of gyration) ratios.
In fact, body modeling is much more than a pre-step of marker tracking. It is the process to lay the foundation for the data analysis. It is the process to define the mechanical system. One needs to confine the scope of the mechanical system and to define its nature with a body model. A body model is indeed a collection of all the relevant pieces of information about the body to be analyzed. The main elements of a body model are the points, segments (rigid bodies), segment groups (systems of rigid bodies), and the joints.
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© Young-Hoo Kwon, 1998-