Repeatability studies of a television/computer system for measuring spinal and pelvic movements.

Repeatability of a television/computer system for measuring spinal and pelvic movements has been studied using both a movement simulator and human subjects. The movement simulator was capable of reproducing independent movements of either pelvis or spine about any one of three mutually perpendicular axes. When the system was tested using this simulator, the least accurate measurement was of the transverse plane movements of the spine. The scatter of the samples about the zero position in each plane for the condition of no movement was also measured using the movement simulator. The standard deviation of the measurements from the mean zero was 1.09 percent in the worst case. The scatter was greatest for transverse plane measurements. Repeatability of measurements using human subjects showed the greatest variation in sagittal plane movement of the pelvis (mean = 3.4 degrees, s.d. = 0.90).