Mathematical analysis of errors resulting from choice of reference frame coordinates in measuring human joint motion
- Lawrence Livermore National Lab., CA (United States)
- Rancho Los Amigos Medical Center, Downey, CA (United States)
Measurements of human joint motion frequently involve the use of opto-electronic and other motion analysis systems where some type of makers are used to establish joint motion within a global reference coordinate frame. Typically, this global reference coordinate frame is chosen to be most convenient for the person carrying out the experiment in which the joint motion is measured, and Euler angles are chosen as the measure of joint motion. Results, however, may be quite arbitrary and therefore rendered meaningless if the reference frame is not properly chosen with respect to the physical joint axis. In order to make a proper choice of coordinate axes in the reference frame, one must take into consideration both the location and the orientation of die physical joint axis relative to the reference frame`s axes. In nature, joint axes can exist at any orientation and location relative to an arbitrarily chosen global reference frame. An axis that is not properly aligned with the global reference frame is therefore called an arbitrary axis. We demonstrate that errors result when measurements and calculations are made in a global reference frame that is arbitrarily placed and oriented, with little regard for the physical axis. Slight offsets of global reference frame produce significant errors in recording rotations about the joint axis. We conclude that, in order to be able to reach valid conclusions from joint motion measurements, the reference frame with respect to which all are taken must be brought to the physical axis; furthermore, one of the reference axes must be aligned with the physical axis. Any other choice of reference axes will result in misleading an often erroneous results.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 80390
- Report Number(s):
- UCRL-JC-119789; CONF-9507124-1; ON: DE95010918
- Resource Relation:
- Conference: 15. Congress of the International Society of Biomechanics, Jyvaskyla (Finland), 2-6 Jul 1995; Other Information: PBD: Feb 1995
- Country of Publication:
- United States
- Language:
- English
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