Concurrent validity and TEST-RETEST reliability of the incremental shuttle walk TEST in patients with type 2 diabetes mellitus

Background: Type 2 diabetes mellitus (T2DM) is a chronic metabolic-endocrine disorder characterized by insulin resistance and relative insulin deficiency. Functional capacity is considered a key determinant of the ability to perform activities of daily living and maintain quality of life, and it is frequently impaired in individuals with T2DM. The Incremental Shuttle Walk Test (ISWT) is a low-cost, externally paced field test used to assess maximal exercise capacity; however, evidence regarding its validity and reliability in individuals with T2DM remains limited. Objective: Investigate the concurrent validity of the ISWT against the Six-Minute Walk Test (6MWT) and determine its test-retest reliability in individuals with T2DM. Methods: Twenty-six individuals with T2DM (16 females, 10 males; mean age 56.0 ± 12.02 years) were included. Concurrent validity of the ISWT was assessed by comparison with the 6MWT. Test-retest reliability was evaluated by repeating the measurements after 7 days, provided that participants' clinical condition remained stable. Statistical analyses were performed using SPSS Statistics version 31. Results: The ISWT demonstrated acceptable-to-good test-retest reliability, with an intraclass correlation coefficient ICC3,1 of 0.778 (95% confidence interval: 0.568-0.893; p < .001). No significant difference was found between the first and second measurements (336.54 ± 102.53 m vs. 323.85 ± 84.95 m; t(25) = 1.032; p = .312), indicating that no statistically significant systematic change was observed between the test and retest assessments. The standard error of measurement (SEM) was 48.3 m, and the minimal detectable change at the 95% confidence level (MDC95) was 134.0 m. Conclusion: The ISWT demonstrated acceptable concurrent validity with the 6MWT and good test-retest reliability in individuals with T2DM. Therefore, it may be a useful tool for assessing functional exercise capacity and objectively evaluating functional status in clinical practice. However, SEM and MDC values should be carefully considered when interpreting individual changes in this population.Clinical Trials Number NCT06519318.