Comparison of scapular kinematics from optical motion capture and inertial measurement units during a work-related and functional task protocol

Understanding scapular motion during everyday tasks is essential for adequate return-to-work and intervention programming, yet most scapular assessments involve restricted motion analysis within a laboratory setting. Inertial measurement units (IMUs) have been used to track scapular motion, but their validity compared to "gold standard" optical motion capture is not well defined. Further, it is unclear how different IMU sensor placements could affect scapular kinematic outcomes during a functional task protocol. To assess the reliability of scapular motion measurements with the use of the "gold standard" optical motion capture and IMUs, and to compare scapular IMU placement to assess which location (acromion or spine) was best for reliability of scapular motion, participants completed two testing sessions. During each lab visit, participant torso, humeri, and scapulae motion was tracked during 3 trials of 8 dynamic tasks and two elevation movements. Scapular angles were extracted during each task. To assess intra-session reliability, intra-class correlation coefficients (ICCs), and root mean square errors (RMSEs) were calculated. Results showed ICCs and RMSEs were acceptable. Although there appeared offsets between the two motion capture system scapular kinematics outcomes based on the plotted waveforms, the movement patterns appeared consistent between both motion capture methods. Data also showed that acromion IMU placement produced slightly more reliable outcomes than placement on the spine. Two placements of scapular tracking IMUs were tested with identical procedures.