Concurrent validity of wearable IMUs for sagittal plane lower-limb range of motion during walking and estimated ground reaction forces: a systematic review and meta-analysis
Azamat Bissenov, Esra Zhubi, Marie Anne Engh, Orsolya Gresits, Réka Tóth, Tamás Terebessy
Abstract
Inertial measurement units (IMUs) offer a portable, affordable alternative to optical motion capture (OMC) systems for gait analysis. This systematic review and meta-analysis evaluated the concurrent validity of IMUs against gold-standard systems (OMC and force plates) for the lower-limb sagittal plane range of motion (RoM) during walking. We also summarized evidence on estimating vertical and anterior–posterior ground reaction forces (GRFs). PubMed, Embase, Web of Science, and Cochrane Central were searched on December 10, 2023 and updated on August 26, 2025. We included studies of ambulatory human participants where IMUs were compared with optical motion capture or force plates for sagittal plane RoM or on estimating vertical and anterior–posterior GRFs. Both observational and randomized designs were eligible. Two reviewers independently screened, extracted data, and assessed study quality (QUADAS-2). Pooled root mean square error (RMSE) values were calculated using random-effects meta-analysis for RoM and GRFs. 27 studies met inclusion criteria; 22 were included in meta-analysis. IMUs showed concurrent validity (RMSE) within the commonly cited threshold ≤ 5° for ankle (RMSE = 4.62°, 95% CI 3.34–5.90) and knee (RMSE = 4.60°, 95% CI 3.60–5.60) sagittal plane RoM, especially during overground walking. Hip concurrent validity was borderline (RMSE = 5.79°, 95% CI 4.39–7.19), with errors amplified on treadmills. Variability (I2 = 90–96%) reflected differences in hardware, placement, calibration, and processing. Estimates of GRFs, particularly vertical (RMSE = 8.37%BW; 95% CI 5.14–11.61) and anterior–posterior components (RMSE = 5.50%BW; 95% CI 2.90–8.09), were less consistent. IMUs provide acceptable concurrent validity (RMSE ≤ 5°) for ankle and knee sagittal plane RoM during walking. Concurrent validity decreases for the hip and treadmill conditions. Standardized calibration, sensor placement, and processing protocols are essential for reliable clinical use, and until further validation, IMUs should be considered complementary rather than stand-alone tools.