Intra and inter-system reliability of a markerless motion capture system in different configurations during...

Markerless motion capture is faster than a traditional marker-based method, but its reliability is not well established. The limitations of this new technology must be understood to ensure its appropriate utilization.

Does a markerless motion capture system exhibit intra-device and inter-device reliability with an Intraclass Correlation Coefficient (ICC) > 0.70 during functional tasks?

Twenty test subjects were asked to squat and walk three times to compute the test-retest (repeated task with the same scaled skeletal model applied) and remove-replace (repeated task with two independently generated skeletal models applied) intra-device reliability for each of three devices and the inter-device reliability between the devices. Two devices were configured in a standard volume, and one device was configured sub-optimally in a larger volume.

For intra-device reliability, the average squat range of motion (ROM) test-retest ICC was 0.86 and average squat remove-replace ICC was 0.74. The average walk ROM test-retest ICC was 0.70 and the average walk remove-replace ICC was 0.72. For inter-device reliability between the two devices in the standard volume, the average ICC was 0.82 for squat and 0.72 for walk. With the sub-optimally configured device included for a three-device analysis the average inter-device reliability ICC dropped to 0.55 for squat and 0.46 for walk.

Larger field of view, suboptimal camera placement and tasks performed away from the center of the field of view presented challenges to the DARI markerless mocap system. Intra-device and inter-device reliability can achieve a level of ICC > 0.7 using DARI markerless mocap technology using an optimized setup, but the transverse plane kinematics exhibit the weakest performance. Optimal camera placement (i.e., field of view) is critical for reliable results.