Assessing Concurrent Validity and Reliability of the S-Gait Insole: A Novel Tool for Measuring Weight Bearing

Objectives: Accurate measurement of weight-bearing (WB) is critical in musculoskeletal and neurological rehabilitation, yet current systems are often costly and impractical for routine use. This study investigated the concurrent validity of the S-GAIT insole, a low-cost and portable tool, compared with the Digital Biometry Scanning System and Milletrix Software (DIASU, Italy). Materials and Methods: A cross-sectional, within-subject comparative design was applied to compare S-GAIT and DIASU. Twenty-one healthy individuals (mean age 32.6 ± 7.3 years) participated. WB of both lower extremities was assessed during quiet standing using both devices in a single laboratory session. Data were collected under standardized static conditions, and outcomes were statistically analyzed. Results: No significant differences were found between S-GAIT and DIASU in WB measures (p > 0.05). Strong Pearson correlations (r = 0.832–0.838, p < 0.001) and high intraclass correlation coefficients (ICC = 0.89–0.94, 95% CI: 0.73–0.95) were obtained. Bland–Altman analysis indicated low standard error of the mean for differences, confirming agreement between systems. Conclusions: The S-GAIT insole provided valid WB measurements when compared with DIASU under static conditions. Its strong psychometric properties and low cost support its potential as an economical, accessible, and clinically useful tool for objective WB quantification. By enabling portable WB assessment and real-time feedback that can be integrated into home-based or remote rehabilitation, the S-GAIT may facilitate patient compliance, telemonitoring, and more individualized therapeutic decision-making in musculoskeletal and neurological care.