Test-Retest Reliability and Minimal Detectable Changes for Wearable Sensor-Derived Gait Stability, Symmetry, and Smoothness in Individuals with Severe Traumatic Brain Injury

Severe traumatic brain injury (sTBI) often results in significant impairments in gait stability, symmetry, and smoothness. Inertial measurement units (IMUs) have emerged as powerful tools to quantify these aspects of gait, but their clinometric properties in sTBI populations remain underexplored. This study aimed to assess the test-retest reliability and minimal detectable change (MDC) of three IMU-derived indices—normalized Root Mean Square (nRMS), improved Harmonic Ratio (iHR), and Log Dimensionless Jerk (LDLJ)—during a 10 m walking test for sTBI survivors. Forty-nine participants with sTBI completed the walking test, with IMUs placed on key body segments to capture accelerations and angular velocities. Test-retest analyses revealed moderate to excellent reliability for nRMS and iHR in anteroposterior (ICC: 0.78–0.95 and 0.94, respectively) and craniocaudal directions (ICC: 0.95), with small MDC values, supporting their clinical applicability (MDC: 0.04–0.3). However, iHR in the mediolateral direction exhibited greater variability (ICC: 0.80; MDC: 9.74), highlighting potential sensitivity challenges. LDLJ metrics showed moderate reliability (ICC: 0.57–0.77) and higher MDC values (0.55–0.75), suggesting the need for further validation. These findings underscore the reliability and sensitivity of specific IMU-derived indices in detecting meaningful gait changes in sTBI survivors, paving the way for refined assessments and monitoring the rehabilitation process of sTBI survivors. Future research should explore these indices’ responsiveness to interventions and their correlation with functional outcomes.