Validity of wearable inertial measurement units for monitoring lower-limb running biomechanics: a comparison with optical motion capture

Wearable inertial measurement units (IMU) provide a portable alternative to optical motion capture (OMC) systems for assessing running biomechanics. However, whether IMU-derived lower-limb kinematics demonstrate consistent agreement with OMC across different joints and kinematic outcomes remains unclear. Twelve recreational runners (5 males and 7 females) completed treadmill running at a fixed (12.0 km·h -1 ) and self-selected (10.5±1.6 km·h -1 ) speeds. Lower-limb sagittal-plane kinematics were obtained using a unified OpenSim musculoskeletal modeling framework. Normality of the waveform data was assessed using the D’Agostino-Pearson K2 test. Statistical parametric mapping (SPM) paired t -tests were used to compare IMU- and OMC-derived joint-angle waveforms across the gait cycle. Agreement between the IMU and OMC systems was evaluated using the coefficient of multiple correlation (CMC), root mean square difference (RMSD), intraclass correlation coefficients (ICC), and Bland-Altman analysis. IMU-derived joint angle waveforms demonstrated excellent waveform similarity with OMC measurements across all joints and running speeds (0.96 ≤ CMC ≤ 0.99). RMSD values ranged from 5.25° to 10.96°, with the smallest differences observed at the knee joint. SPM revealed joint- and phase-dependent differences, primarily at the hip and ankle joints, while minimal differences were observed for the knee. Agreement for discrete variables was weaker than waveform similarity. However, knee range of motion demonstrated excellent agreement across both running conditions (0.93 ≤ ICC ≤ 0.95). Similar agreement patterns were observed between fixed-speed and self-selected running. Wearable IMUs demonstrated excellent waveform similarity with OMC for capturing lower-limb movement patterns during running but showed variable agreement for discrete joint kinematic measures. These findings support the use of IMU systems for monitoring running biomechanics, while specific kinematic variables should be interpreted considering their quantitative measurement limitations.