Validity And Reliability Of Inertial Measurement Units For Pelvic Orientation Assessment: A Systematic Review.

Pelvic orientation assessment is fundamental for gait, posture, and sport biomechanics; however, using laboratory-based motion-capture systems is costly and restricted to controlled environments. Inertial measurement units (IMUs) offer a portable alternative to traditional laboratories but differ in placement, calibration, and sensor-fusion settings/protocols, which could complicate interpretation in clinical practice. Therefore, this systematic review examined the validity and reliability of IMU-based pelvic orientation during functional and sport-specific tasks. PubMed, Web of Science, and IEEE Xplore were searched for relevant studies that assessed pelvic orientation (e.g., tilt, obliquity, or rotation) using IMUs, and the findings were reported using PRISMA guidelines. Eligible studies included those reporting data from human participants and reporting either the validity or reliability of IMUs against optical motion-capture systems. Twelve studies met the inclusion criteria and were checked using a 12-item methodological quality tool. Our IMU validity findings varied across the included studies; pelvic tilt demonstrated the highest accuracy, with root-mean-square error (RMSE) values typically between 0.2° and 4.9° and minimal mean differences in recent studies. Obliquity and rotation showed greater variability, with RMSE values reaching 6°-11° during high-speed running. Our IMU reliability findings indicated good-to-excellent repeatability even during continuous functional activity (intraclass correlation coefficient (ICC) 0.87-1.00). Conversely, reliability was poor for pelvic tilt in individuals following total hip arthroplasty (ICC = 0.08). IMUs appear to provide useful pelvic orientation measurements, particularly in controlled tasks and when sacrum-based placement is used. However, validity is more variable for pelvic obliquity and rotation, during high-speed or complex movements, and in clinical populations. Further research is required to standardize protocols, improve reporting, and clarify performance across different applications.