Assessment of Postural Stability Using an Affordable and Simple Force Platform

Stability assessment of human posture is an important part in supporting the diagnosis of doctors in the departments of medical rehabilitation, physiotherapy, and audiology. This study proposes a simple and inexpensive assessment system that can be used as an alternative to the existing commercial system by using a Wheatstone bridge with eight load cells that are placed in such a way at the bottom of a plate. Calculations of COP (Center of Pressure) and Approximate Entropy (ApEn) were used to measure the stability of the test subject's posture when standing on the platform in time series represented in the statokinesigram and stabilogram mappings as a planar trajectory of the COP when the subject controls the body balance. The test result of trajectory mapping in this study demonstrated that the test subject showed the body tendency to maintain a stable posture in the anterior-posterior (AP) and the medial-lateral (ML) directions. Approximate Entropy is then used as an indicator for assessing the COP oscillations. A consistent, greater number of ApEn values is resulted in this study with $\gamma$ value of 0.2 that indicates postural stability of quiet, standing subjects, as reported in some literatures. The developed system is capable of presenting the regularity increasing of human postural sway or stability.