In search of the homunculus

The purpose of this paper is to create a structural framework that enables us to understand the way that gait analysis should be performed and thus how all the different processes are integrated. There are essentially two types of problems in rigid body mechanics: the Direct Dynamics Problem in which the forcing functions are known and the objective is to determine the resulting motion (this is the approach the homunculus pursues); and the Inverse Dynamics Problem in which the motion is specified and the objective is to find the forcing functions causing that motion (this is the approach the gait analyst pursues). We have developed a software package that enables those who have only an IBM PC (or compatible) computer to perform detailed 3D gait analysis. There are four input data files: electromyography; anthropometry; 3D segment displacements; and 3D ground reaction forces and the program GAITMATH is used to derive another six files. There are over 240 variables which can be viewed with the program GAITPLOT. This powerful, interactive environment allows both the novice and experienced gait analyst to explore the various interconnections between the neural, muscular, skeletal and external systems.