Reliability and validity of the WATSMART three-dimensional optoelectric motion analysis system

Reliability and validity of the WATSMART (Waterloo Spatial Motion Analysis Recording Technique) system was evaluated under static and dynamic conditions. In experiment 1, infrared light-emitting diodes (IREDs) were placed at the axis and along the arms of a clinical goniometer. Twelve angles in 5-degree increments were each recorded 10 times at each of three spatial locations. Reliability was assessed using intraclass correlation coefficients (ICCs) and analysis-of-variance procedures to determine within-trial variability. The ICCs for all spatial locations exceeded .99. The 95% confidence interval for each angle was less than 0.5 degree in all cases. Criterion-referenced instrument validity was assessed with regression analysis. Slopes of the regression of reconstructed angle on reference angle were close to unity for each spatial location. A systematic error, however, that increased as the goniometer was rotated 45 degrees away from the cameras was evident. In experiment 2, a robotic arm was fitted with four IREDs and made to repeat a defined movement trajectory 10 times at each of three spatial locations. The ICCs for portions of each trajectory ranged from .20 to .99. The results show that reliable and valid results can be obtained from this motion analysis system if adequate precautions are taken to reduce unwanted light reflections. Reliability and validity decreased somewhat as the object was rotated further away from the plane in which the cameras were mounted.