Whole Body Center of Mass Estimation with Portable Sensors: Using the Statically Equivalent Serial Chain and a Kinect

Abstract

The trajectory of the whole body center of mass (CoM) is useful as a reliable metric of postural stability. If the evaluation of a subject-specific CoM were available outside of the laboratory environment, it would improve the assessment of the effects of physical rehabilitation. This paper develops a method that enables tracking CoM position using low-cost sensors that can be moved around by a therapist or easily installed inside a patient's home. Here, we compare the accuracy of a personalized CoM estimation using the statically equivalent serial chain (SESC) method and measurements obtained with the Kinect to the case of a SESC obtained with high-end equipment (Vicon). We also compare these estimates to literature-based ones for both sensors. The method was validated with seven able-bodied volunteers for whom the SESC was identified using 40 static postures. The literature-based estimation with Vicon measurements had a average error 24.9 ± 3.7 mm; this error was reduced to 12.8 ± 9.1 mm with the SESC identification. When using Kinect measurements, the literature-based estimate had an error of 118.4 ± 50.0 mm, while the SESC error was 26.6 ± 6.0 mm. The subject-specific SESC estimate using low-cost sensors has an equivalent performance as the literature-based one with high-end sensors. The SESC method can improve CoM estimation of elderly and neurologically impaired subjects by considering variations in their mass distribution.

Biomechanical Analysis of Rehabilitation Exercises Performed During Serious Games Exercises

“…Concerning the Kinect there are studies exploring the possibilities of this device for posture assessment [6], gait analysis [7], functional evaluation [8] … The Kinect is a markerless motion capture system that provides a simple skeleton model allowing full body analysis [9]. Such kind of system seems to be accurate enough to track and monitor patients body movements during simple rehabilitation exercises.…”

Uso del Centro de Masa Personalizado para la Evaluaci´on del Equilibrio

“…Asimismo, la calidad de la estimación personalizada del CoM depende de la capacidad del sujeto para realizar la identificación SESC. Aún si esta técnica ha sido validada anteriormente [10][11][12] el presente estudio marca la primera vez que se aplica a una población con problemas de equilibrio lo que dificultó la obtención CoM satisfactorio. Sin embargo, como se observa en la Fig.…”

“…Los errores que esto origina son evidentes en poblaciones para las que existen pocos estudios antropométricos, por ejemplo, la tercera edad, o con discapacidades motoras [17]. Uno de los métodos que permiten la obtención de un CoM personalizado es la técnica SESC [9,12] …”

“…1a. Detalles adicionales acerca de la definición e identificación de estos parámetros se encuentran en [9,12].…”

“…En trabajos anteriores, hemos muestrado que el método Statically Equivalent Serial Chain (SESC) es eficaz para la creación de un modelo personalizado del CoM libre de las restricciones antes mencionadas [9,10]. Anteriormente, el uso de la SESC ha sido validado para individuos de la tercera edad sin problemas de equilibrio [11] y para individuos jóvenes [10,12]; así mismo, la posición y aceleración del CoM personalizado han sido usadas para estimar la el equilibrio de una persona durante movimientos libres [13]. Este presenta la primera aplicación del SESC a pacientes neurológicos, buscando explorar los usos clínicos del método (efectividad, facilidad de aplicación, etc).…”