title: Accuracy and repeatability of joint angles measured using a single camera markerless motion capture system.
abstract: Markerless motion capture systems have developed in an effort to evaluate human movement in a natural setting. However, the accuracy and reliability of these systems remain understudied. Therefore, the goals of this study were to quantify the accuracy and repeatability of joint angles using a single camera markerless motion capture system and to compare the markerless system performance with that of a marker-based system. A jig was placed in multiple static postures with marker trajectories collected using a ten camera motion analysis system. Depth and color image data were simultaneously collected from a single Microsoft Kinect camera, which was subsequently used to calculate virtual marker trajectories. A digital inclinometer provided a measure of ground-truth for sagittal and frontal plane joint angles. Joint angles were calculated with marker data from both motion capture systems using successive body-fixed rotations. The sagittal and frontal plane joint angles calculated from the marker-based and markerless system agreed with inclinometer measurements by <0.5°. The systems agreed with each other by <0.5° for sagittal and frontal plane joint angles and <2° for transverse plane rotation. Both systems showed a coefficient of reliability <0.5° for all angles. These results illustrate the feasibility of a single camera markerless motion capture system to accurately measure lower extremity kinematics and provide a first step in using this technology to discern clinically relevant differences in the joint kinematics of patient populations.
authors: Division of Physical Therapy, University of Kentucky, United States.
authors: Anne
authors: A
authors: Schmitz
authors: Department of Computer Science, University of Kentucky, United States.
authors: Mao
authors: M
authors: Ye
authors: Department of Kinesiology and Health Promotion, University of Kentucky, United States.
authors: Robert
authors: R
authors: Shapiro
authors: Department of Computer Science, University of Kentucky, United States.
authors: Ruigang
authors: R
authors: Yang
authors: Division of Physical Therapy, University of Kentucky, United States. Electronic address: b.noehren@uky.edu.
authors: Brian
authors: B
authors: Noehren
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D007596:Joints / Q000502:physiology*; D035002:Lower Extremity; D009038:Motion; D009068:Movement; D011187:Posture; D015203:Reproducibility of Results; D012399:Rotation
keywords: Accuracy and reliability; Joint angles; Microsoft Kinect; Motion capture