Reliability and validity of a smart insole incorporating inertial measurement unit and pressure sensors for spatiotemporal gait parameters

Background: Although smart insoles have emerged as promising tools for long-term gait analysis, these devices face a trade-off between wearability (where sensor modules are fully accommodated within a compact insole) and data quality (where sensor modules cannot be accommodated within the insole). Integrating an inertial measurement unit (IMU) with pressure sensors and fully embedding all modules may resolve this trade-off; however, the reliability and validity of such a smart insole remain unverified. Research question: Can a smart insole with an IMU and pressure sensors provide reliable and valid spatiotemporal gait parameters comparable to an instrumented walkway? Methods: Twenty-six healthy volunteers (mean age 26.0 ± 5.6 years) performed walking tasks while wearing the smart insole. Reliability was assessed by comparing spatiotemporal parameters between two sessions of walking trials. Validity was evaluated against a gold-standard instrumented walkway positioned along the path. Data were analyzed using intraclass correlation coefficients (ICCs) and Bland–Altman analysis. Results: ICC values indicated good to excellent reliability (0.93–0.95) and validity against the instrumented walkway (0.70–0.99). Although Bland–Altman analysis revealed systematic differences, these deviations were acceptable (<4% of mean difference), with 95% limits of agreement ratios under 8% for all parameters. Significance: The smart insole incorporating IMU and pressure sensors, characterized by a highly wearable and cable-free design, provides reliable and valid spatiotemporal gait parameters. Future studies involving broader populations and real-world settings are warranted to further validate its applicability.