Validity and reliability of trunk and lower-limb kinematics during squatting, hopping, jumping and side-stepping using OpenCap markerless motion capture application

• Published in: Journal of sports sciences Vol. 42; no. 19; pp. 1847 - 1858
• Main Authors: Lima, Yuri Lopes, Collings, Tyler, Hall, Michelle, Bourne, Matthew N., Diamond, Laura E.
• Format: Journal Article
• Language: English
• Published: England Routledge 01-10-2024; Taylor & Francis Ltd
• Subjects: Accuracy; biomechanics; Jumping; Kinematics; measurement; Motion capture; repeatability; Validity; repeatability; Accuracy; biomechanics; measurement
• ISSN: 0264-0414; 1466-447X; 1466-447X
• DOI: 10.1080/02640414.2024.2415233

OpenCap is a web-based markerless motion capture platform that estimates 3D kinematics from videos recorded from at least two iOS devices. This study aimed to determine the concurrent validity and inter-session reliability of OpenCap for measuring trunk and lower-limb kinematics during squatting, hopping, countermovement jumping, and cutting. Nineteen participants (10 males, 9 females; age 27.7 ± 4.1 years) were included. Countermovement jump, single-leg triple vertical hop, single-leg squat, sidestep cutting and side hop tasks were assessed. For validity, OpenCap was compared to a marker-based motion capture system using root-mean-square error. Test-retest reliability of OpenCap was determined using intraclass correlations and minimum detectable change (MDC) from two testing sessions. The squat had the lowest RMSE across joint angles (mean = 7.0°, range = 2.9° to 13.6°). For peak angles, the countermovement jump (jump phase) (ICC = 0.62-0.93) and the squat (ICC = 0.60-0.92) had the best reliability across all joints. For initial contact, the side hop had the best inter-session reliability (ICC = 0.70-0.94) across all joint angles. As such, OpenCap validity and reliability are joint and task specific.