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1.4 Choices

APAS/Gait represents a flexible tool for the analysis of gait. It is primarily intended for walking but it may be used for running as well.

Depending on the equipment of the actual gait lab the following scenarios could be imagined:

One camera and no force platform.

This will allow a 2D-analysis of kinematics, i.e. joint angles, angular velocity, step length and step frequency. Note that 2D analysis is not currently supported by APAS/Gait.

One camera and one force platform.

Besides kinematics this setup opens for calculation of net joint moments on one leg in two dimensions. Note that 2D analysis is not currently supported by APAS/Gait.

Three cameras and one force platform.

This allows kinematics and 3D inverse dynamics for one leg. However, four cameras would make things easier, since all markers must be seen by at least two cameras.

Four, five or six cameras and two force platforms.

Five cameras are considered optimal for a full blown three-dimensional gait analysis. This setup will allow 3D kinematics and 3D inverse dynamics of both legs.

If only the sagittal plane and only one leg is of interest for inverse dynamics, it is sufficient to go with a two-dimensional approach. The joint moments have been shown to be highly identical for flexion/extension when analyzed by a two- or three-dimensional method, respectively.

In general a kinetic analysis of walking is by far superior to an analysis of kinematics only. The inverse dynamics method provides highly sophisticated information about muscle forces and contraction form. Also muscle power and muscle work may be calculated by inverse dynamics. With a pure analysis of kinematics, one will often end up with no information at all regarding the function of a patient before or after surgery. The differences may very well be "hidden" in the kinetics. For example, it is only possible to tell which joint is loaded the most by use of inverse dynamics.

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