Concurrent Validity of a Belt-Type IMU for Postural Sway Measurement: A Pilot Comparison with a Force Plate and Vision-Based System

Postural sway analysis is a widely used biomechanical indicator to assess balance control and fall risk in the elderly and patients with neuromuscular disorders. Although force plates are considered the gold standard for measuring the center of pressure (COP), their high cost and limited portability hinder clinical and community-based use. Recently, IMU sensors have been adopted as compact and wearable alternatives, but the concurrent validity of IMU-derived postural sway remains to be clarified. This pilot study aimed to preliminarily assess concurrent relationships between a belt-type IMU system (100 Hz) and reference systems for postural sway measurement by comparing its outcomes with those of a force plate and a vision-based system. Three healthy adults participated in static standing tests under eyes-open and eyes-closed conditions. Postural sway parameters, including COP displacement and mean velocity, were simultane-ously recorded by all three systems. Pearson correlation, linear regression, and intraclass correlation coefficients (ICC [2,1]) were used to assess correlation and inter-device agreement. The IMU-derived sway parameters showed strong correlations with both the force plate (r = 0.869-0.904) and the vision system (r = 0.882-0.939). Linear regression anal-yses demonstrated coefficients of determination ranging from R 2 = 0.75 to 0.88. The ICC results indicated moderate agreement with the force plate and moderate-to-good agreement with the vision-based system, and should be interpret-ed cautiously given the pilot sample size. These preliminary findings suggest that the belt-type IMU system yields pos-tural sway metrics that are strongly correlated with laboratory-based systems, with varying levels of agreement de-pending on the reference device. Larger-scale studies are warranted to confirm agreement and clinical utility in diverse populations and tasks.