Measurement of human back movements in three dimensions by opto-electronic devices.

Two systems for the measurement of the movement of retro-reflective markers in three-dimensional space have been used to measure rotations of the human back. Both the CODA-3 and the VICON devices used are available commercially. Both devices were shown to be capable of producing reproducible data on three-dimensional rotations. However, neither system was shown to be ideal due to the difficulty of maintaining the markers in the field of view. In particular, the CODA-3 system was found to be severely limited in this application due to the problem of cross-over conflict between the retro-reflective prisms that results in the loss of data. The VICON system was found to be more flexible but data analysis requires an interactive input from the operator and so can be very time consuming.