4. Accuracy of Electrogoniometers and Potentiometers

 It is not uncommon for the accuracy of angular displacement of video-based motion analysis to be assessed in comparison with electrogoniometric techniques. However, for this to be useful the possible sources for error using electrogoniometers need to be considered.

Possible sources of error when assessing human motion include:

■ Movement of the end blocks of the electrogoniometer on soft tissue around a joint;

■ Placement of the electrogoniometer in the correct plane of interest to eliminate crosstalk between two planes of motion, e.g. adduction and abduction, or rotation with sagittal plane movement; or

■ The limiting mechanical properties of the strain gauge wire giving a finite accuracy of angular displacement measurements.


 When used to study the accuracy of video-based motion analysis systems, if set up carefully, all but the last source of error should be eliminated.

Nicol (1987, 1989) reported that the error in the measurement of angular displacements due to the mechanical proper-ties of the strain gauge wire was within 1°. Therefore, accurate joint angular motion may be attained with careful placement of electrogoniometers