Center of Mass Estimation Using Kinect and Postural Sway

Abstract

The Center of Mass (CM) plays an important role in balance assessments due to its physical definition. And the knowledge of its behavior provides information that may help the implementation of protocols to aid physiotherapy with a view of improving postural control capacities in some people. In this work, the kinematic method (segmental method) was used to estimate the human body CM, and this was only possible by knowing some joints locations in body. So, the Kinect device was used to provide the joints because its consistence and facility of use, also for its markerless method of recognizing human joints. After calculating all segmental CM by the anthropometric parameters and using the endpoints (joints), the total body CM was estimated. A male subject 1.67 m high and 60 kg mass participated of the initial test and a static task was performed to acquire data to the analysis. The subject remained standing still during 30 s in a comfortable standard position at about 2 m of the Kinect. The subject also performed a voluntary oscillation task. As result were obtained two graphs that represent the CM trajectory along the AP-ML plane (statokinesiogram) and the amplitude of CM displacement across time (stabilogram) and one graph representing the voluntary oscillation around the ankle. The results also showed the CM location in percentage being 57.56 ± 0.10, that can be compared to the physiological CM being 55%, what is quite good estimation. Therefore, the potential of this low-cost photogrammetric device is noticeable to compose a method of CM estimation and also for studies in balance assessments.