(18) TECHNOLOGICAL RELIABILITY OF A THREE-DIMENSIONAL MARKERLESS MOTION CAPTURE SYSTEM FOR ASSESSING KINEMATIC DATA

Advances in motion capture technology include markerless systems to facilitate valid data collection. Reliability of this technology includes both biological and technological variability.

Purpose: The aim of this study was to determine the inter-device technological reliability for a 3-dimensional markerless motion capture system to quantify 214 basic kinematic variables.

Methods: Twenty healthy men (n = 11, hgt = 181.0±7.2 cm, body mass = 87.7±11.1 kg, age = 26.8±6.8 yrs) and women (n = 9, height = 167.0±6.6 cm, body mass = 62.7±6.9 kg, age = 24.2±7.3 yrs) participated in this study. All subjects performed a standardized test battery consisting of 29 different movements, from which 214 different kinematic metrics were derived. These variables (with the number of variables in parentheses) included range of motion in degrees for both the right and left the shoulder (28), hip (40), knee (26), and ankle (26). Also torso rotation, flexion and extension (28), lower limb summery flexion (26), knee valgus (26), pelvis rotation (6), and lunge stride length (4). Cameras for two three-dimensional markerless motion capture systems (DARI Motion, Lenexa, KS) located immediately adjacent (3 cm apart) to each other were utilized to quantify movement characteristics. Independent sample t-tests with selected reliability statistics (i.e., intraclass correlation coefficient, effect sizes, mean absolute differences) were used to evaluate agreement between the two systems (p< .05).

Results: Results indicated that 95.7% of all metrics analyzed revealed negligible or small between-device effect sizes (ES £ 0.50). Further, 91.6% of all metrics analyzed showed moderate or better agreement based on ICC values (ICC ³ 0.50), while 32.2% of all metrics showed excellent agreement (ICC ³ 0.90). For the 198 metrics measuring joint angles, the mean difference between systems was 2.9 degrees, while for metrics investigating distance measures (16 metrics; e.g., center of mass depth, stride length), the mean difference between systems was 0.62 cm. Only 1.9% of all variables (4/214) were significantly different.

Discussion: These results indicate almost all of the kinematic variables measured demonstrated technical reliability. Readers should be cognizant that this technological reliability is in part movement and metric dependent, and is independent of movement variability (biological) from when a subject performs repeated testing. Caution is advised when trying to generalize study findings beyond the specific technology and software used in this investigation. Practical Applications: Given the technological reliability reported in this study, as well as the logistical and time-related limitations associated with marker-based motion capture systems, these data support the use of markerless motion capture technology to reliably measure movement characteristics of athletes and patients with greater ease.

Acknowledgements:

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