Evaluation of human body balance ability through geometric solution based on an equivalent model using an RGB camera

Many studies have reported that human body balance ability was essential in the early detection and self-management of chronic diseases. However, the methods to measure balance, such as motion capture and force plates, are so expensive and require space for setting up the system. Furthermore, the evaluation results are too difficult to understand without specialized knowledge. Thus, there is a need for a low-cost device and an evaluating method that anyone can easily understand. This study proposed evaluating human body balance ability through a geometric solution based on an equivalent model using a single low-cost RGB camera. When each ratio of body weight was assigned to human-pose-estimation-based key points, the user's center of mass (COM) could be estimated. An equivalent model, the inverted pendulum on the wobble balance board (WBB), consisted of two joints: the joint as the human body made the body movement for the stable condition, and the other as the WBB was the free joint. The algorithm to utilize the geometric solution of the equivalent model with Perpendicular Projection Point (PPP) enabled us to evaluate the human body balance ability on the board. The experimental results confirmed that the proposed approach was easy to understand even without professional knowledge. Although it was known that the general method was to use the COM, it was discussed that our proposal with PPP was more effective because the WBB plane was movable. And we can demonstrate the factors which affected the balance ability on the WBB in this study.