Mechanical testing for three-dimensional motion analysis reliability

• Mechanical tests were used to evaluate the reliability of motion analysis systems.
• Three tests were conducted at four labs with varying equipment and configurations.
• Results demonstrate system accuracy and reliability can be obtained across labs.
• Testing is important for multi-center studies to assure data consistency.

The purpose of this study was to use simple mechanical tests to evaluate the reliability of three-dimensional motion analysis systems and biomechanical models. Three different tests were conducted at four motion analysis laboratories where clinical care and research studies are routinely performed. The laboratories had different motion capture systems, different types and number of cameras, different types and numbers of force plates and different biomechanical models. These mechanical tests evaluated the accuracy of the motion capture system, the integration of the force plate and the motion capture system, and the strength of the biomechanical model used to calculate rotational kinematics. Results of motion capture system accuracy tests showed that, for all labs, the error between the measured and calculated distances between markers was less than 2 mm and 1 ° for marker separations which ranged from 24 mm to 500 mm. Results from the force plate integration tests demonstrated errors in center of pressure calculation of less than 4 mm across all labs, despite varied force plate and motion system configurations. Finally, errors across labs for single joint rotations and for combined rotations at the hip and knee were less than 2 ° at the hip and less than 10 ° at the knee. These results demonstrate that system accuracy and reliability can be obtained allowing the collection of comparable data across different motion analysis laboratories with varying configurations and equipment. This testing is particularly important when multi-center studies are planned in order to assure data consistency across labs.