Abstract: BACKGROUND: The optical three-dimensional motion capture system is widely used in physiology or pathology, in vitro or in vivo experiments, medical treatment or life, but there is no objective analysis of the accuracy of the system and its influencing factors.  
OBJECTIVE: To establish optical three-dimensional motion capture system to analyze its accuracy and influencing factors for biomechanical testing.
METHODS:  First, the optical three-dimensional motion capture system camera was installed to a semi-arc wave position to capture 18 sets of coordinate data of static marker points, each set of 400 coordinate values. The system precision was calculated. The robot arm was used to complete the movement along the coordinate axis X, Y and Z axis, and the obtained coordinate data were processed by MATLAB to calculate the movement distance (measured value). Second, the accuracy of the motion capture system was calculated based on the actual value of the electronic micrometer. Finally, according to the aforementioned precision and accuracy test method, one-way analysis of variance was used to analyze whether there were differences in the precision and accuracy of the system under different motion directions, various coordinate axes, indoor lighting, different camera numbers, different Marker sizes and materials, and different camera position variables.  
RESULTS AND CONCLUSION: (1) When the optical three-dimensional motion capture system camera was placed in a semi-arc wave, the X, Y and Z axis coordinate precisions were 5.00, 10.26, and 5.50 μm, respectively, and the accuracies of the movement along the X, Y and Z axes were: 15.58, 20.69, and 12.24 μm. (2) As the camera changed from a single-sided shape to a ring shape, the accuracy gradually increased, and the accuracy was optimal when placed in a ring. (3) The presence or absence of starting lighting in the room had no significant impact on the accuracy of the system. (4) As the number of cameras increased, the precision of the capture system rised, but when the number reached a certain level, the precision would approach its limit. (5) In this system, there was no difference in the precision of the Marker points of plastic rigid 12.7, 14.0, 15.9 mm and rubber material with a diameter of 14.0 mm. (6) Therefore, the number of cameras and the placement position of the optical 3D motion capture system have an impact on the accuracy of the system. The size and material of the Marker, the direction of movement, and the indoor lighting have no significant impact on the accuracy of the system. The precision and accuracy of the system meet the needs of biomechanical testing.

Key words: motion capture, optical three-dimensional motion capture system, precision and accuracy, biomechanics