Assessment of reliability and concurrent validity of a single trunk-based IMU system to quantify spatiotemporal parameters in healthy individuals

Background: Commercially available Inertial Measurement Units (IMU) are gaining popularity in clinical gait analysis. Compared to standard optoelectronic motion capture systems (OMCs), IMUs offer advantages such as lower cost, greater time efficiency, and the ability to be used outside of laboratory settings. IMUs can be attached to various body parts and have already been tested in numerous clinical studies. This study aimed to assess the intra-session reliability and concurrent validity of a trunk-based IMU system (BTS G-Walk®) in healthy individuals compared to an OMC system (VICON®). Methods: To test the intra-session reliability and concurrent validity of the BTS-G-Walk®, 27 healthy participants were recruited for gait analysis. Both the IMU and OMC systems were used simultaneously to record spatiotemporal gait parameters under a standardized laboratory protocol. Eight spatiotemporal parameters were analyzed, using the Intraclass Correlation Coefficient (ICC 2,k) and Bland–Altman analysis to evaluate the reliability and concurrent validity. Results: The IMU demonstrated excellent intra-session reliability across all parameters (ICC: 0.952–0.995). Concurrent validity was good to excellent for cadence, speed, stride length, and stride duration (ICC: 0.807–0.999), but poor for stance phase, single support, double support, and swing phase (ICC: 0.036–0.136). Bland–Altman analysis showed the lowest mean percentage bias for cadence (− 0.18%) and the highest for double support phase (23.45%). Conclusion: The BTS-G-Walk® delivers reliable values in healthy individuals. Regarding concurrent validity, stride duration and cadence demonstrated the highest agreement with the reference system. Caution is advised when using the IMU in clinical practice, particularly for interpreting parameters dependent on toe-off events, such as gait phase durations.