(18) BIOLOGICAL RELIABILITY OF A MOVEMENT ANALYSIS ASSESSMENT USING A MARKERLESS MOTION CAPTURE SYSTEM

Advances in motion capture technology include markerless systems to facilitate valid data collection. Recently, the technological reliability of this technology has been reported for human movement assessments. To further understand sources of potential error, biological reliability must also be determined.

Purpose: The aim of this study was to determine the day-to-day reliability for a three-dimensional markerless motion capture system to quantify 4 movement analysis composite scores, and 81 kinematic variables.

Methods: Twenty-two healthy men (n=11; X±SD; age=23.0±2.6 yrs, hheight=180.0±4.8 cm, weight=80.4±7.3 kg) and women (n=11; age=20.8±1.1 yrs, hheight=172.2±7.4 cm, weight=68.0±7.3 kg) participated in this study. All subjects performed 4 standardized test batteries consisting of 19 different movements on four separate days, from which 81 kinematic metrics, and 4 composite scores for overall movement assessments were obtained. These variables (with the number of variables in parentheses) included range of motion in degrees for both the right and left shoulders (12), hips (20), knees (16), ankles (16), torso rotation, flexion and extension (3), and knee valgus (4).  Distances for lunge stride length (2) and center of mass displacement (8) were also measured. A three-dimensional markerless motion capture system (DARI Motion, Lenexa, KS) using 8 cameras surrounding the testing area was used to quantify movement characteristics. 1x4 RMANOVAs determined sig. differences across days for the composite movement analysis scores, and RM-MANOVAs were used to determine test day differences for the kinematic data (p< 0.05). ICCs were reported for all variables to determine test reliability. To determine biological variability, mean absolute differences from previously reported technological variability data (Philipp et al. 2023) were subtracted from the total variability data from the present study.

Results: No differences were observed for any composite score (i.e., athleticism, explosiveness, quality, readiness; p<span style="font-family: Symbol; mso-ascii-font-family: Calibri; mso-ascii-theme-font: minor-latin; mso-hansi-font-family: Calibri; mso-hansi-theme-font: minor-latin; mso-char-type: symbol; mso-symbol-font-family: Symbol;">³0.812) or any of the 81 kinematic variables (p³0.119). Furthermore, 84 of 85 variables measured exhibited good to excellent ICCs (0.61-0.99). When compared to previously reported technological variability data, 66.9% of item variability was due to biological variability, with 66 of 85 variables exhibiting biological variability as the primary source of error (i.e., >50% total variability).

Discussion: These results indicate all of the variables measured with this particular markerless motion capture technology exhibited strong inter-day reliability. Furthermore, the primary source of error was biologic in nature, meaning most of the test variability was due to individuals not performing the movements identically, not due to error from the technology. Since all of the subjects were healthy and physically fit, all test results were relatively homogenous, thus adding to the strength of these reliability results. PRACTICAL APPLICATIONS: As with any human performance testing, when performing movement analyses with three-dimensional markerless motion capture technology, it is critical to provide accurate, consistent and understandable instructions to the subject to minimize movement variability. Furthermore, visual inspection of the movement is recommended to ensure the desired movement is being performed as instructed. Finally, markerless motion capture technology is capable of providing reliable movement analysis data when used correctly.

Acknowledgements:

This project was supported by the Clara Wu and Joseph Tsai Foundation