THREE-DIMENSIONAL KINEMATICS AND KINETICS - Biomechanics and Motor Control of Human Movement - page 176

THREE-DIMENSIONAL
KINEMATICS AND KINETICS

7.0 INTRODUCTION

Over the past 20 years, there have been major commercial developments in
three-dimensional (3D) hardware and software. Chapter 3 included descrip-
tions of some of the 3D imaging systems that have been introduced. The
majority of the systems are television-based, with multiple-camera arrange-
ments requiring passive reflective markers, while other systems use active
infrared emitting diodes (IRED) markers and infrared sensors. Regardless of
the system used, the output of the data collection stage is a file of x , y , z
coordinates of each of the markers at each sample point in time. These coor-
dinates are in the global reference system (GRS) that is fixed in the laboratory
or data collection space. The purpose of this chapter is to go through the steps
where these coordinate data are transformed into the anatomical axes of the
body segments so that a kinetic analysis can be done in a similar manner, as
has been detailed for two-dimensional (2D) analyses in Chapters 3, 5, and 6.

7.1 AXES SYSTEMS

There are several axes reference systems that must be introduced in addition
to the GRS already introduced. The markers that are placed on each segment
provide a marker axis system that is a local reference system (LRS) for each
individual segment. A second LRS is the axis system that defines the principal
axis of each segment. Because skeletal landmarks are used to define these
axes, this system is referred to as the anatomical axis system.