Test–retest and inter-rater reliability of the incremental shuttle walk test in healthy university students

Background Although the Incremental Shuttle Walk Test (ISWT) is commonly used in clinical and research settings, data on its reliability and measurement error indices remain insufficient. Aims To investigate the test–retest and inter-rater reliability of the ISWT in healthy university students and to establish reference values for measurement error indices. Methods Forty-nine participants were recruited, of whom 45 completed all testing procedures. Each participant performed four ISWTs—two administered by Rater 1 and two by Rater 2—across two sessions conducted 2–7 days apart. Test–retest and inter-rater reliability were assessed using intraclass correlation coefficients (ICC), standard error of measurement (SEM), minimal detectable change at the 95% confidence level (MDC 95 ), and Bland–Altman analyses. Results The mean ISWT distance was 638.44 ± 103.50 m and 646.67 ± 109.44 m for Rater 1 across sessions (p=0.255), and 621.11 ± 123.33 m and 654.00 ± 142.53 m for Rater 2 ( p < 0.001). Test–retest reliability was good to excellent, with ICCs of 0.899 for Rater 1 and 0.873 for Rater 2. Corresponding SEM and MDC 95 values were 33.83 m/93.71 m and 47.43 m/131.39 m, respectively. Inter-rater reliability was also good to excellent, with ICCs of 0.869 in Session 1 and 0.899 in Session 2. Bland–Altman analyses confirmed acceptable agreement. Conclusions The ISWT demonstrated good to excellent test–retest and inter-rater reliability, providing novel reference values for measurement error indices. These findings support its use as a reliable tool for assessing functional exercise capacity in both clinical and research settings. Clinical trial registration ClinicalTrials.gov (Identifier: NCT06638281).