The reliability of postural sway measures using the 3space Tracker

Objective. To investigate the reliability of three-dimensional postural control sway measures, in a normal population, using an electromagnetic device. Design. A repeated measures design was used within and between sessions. Background. Electromagnetic measurement has been proposed as a method of measuring postural sway; however, reliability within a normal population has not been shown. Method. An electromagnetic device, the 3image Tracker, measured postural sway at the pelvis using sway path length and displacements in the anterior-posterior, medial-lateral and vertical direction. Ten subjects performed a postural control task involving two trials for six different sensory conditions, on two separate occasions, two weeks apart. Results. The reliability of the technique was demonstrated by the repeatability of results for individual subjects within and between sessions. Individual subjects and sensory conditions were discriminated. Sway path length was the most consistent of the measures used. Conclusions. Three dimensional measures of postural sway are reliable and discriminatory in a normal population.