Intra-session reliability of the Imagined Timed Up and Go Test: intra- and simultaneous inter-rater analyses in community-dwelling older adults.

BACKGROUND: Increased Estimation error (EE), the discrepancy between motor imagery and actual physical function, is reportedly a fall-related risk factor. The reliability of the Imagined Timed Up and Go Test (ITUG) for community-dwelling older adults remains unclear, warranting quantitative assessment before broad clinical use. PURPOSE: We aimed to evaluate the ITUG's intra-session intra-rater and inter-rater reliability. METHODS: Timed Up and Go Test (TUG) and ITUG were performed in older adults with normal cognitive function. EE was defined as ITUG-TUG and Delta time (%) as (TUG-ITUG)/TUG × 100; negative EE and positive Delta time both indicate overestimation of physical ability. Intra-rater reliability was evaluated using repeated within-session measurements and inter-rater reliability using simultaneous timing of the same performance by two examiners within one same-day session. Intra-rater and inter-rater reliability were evaluated by calculating intraclass correlation coefficients (ICCs) using a two-way mixed-effects, absolute-agreement, single-measures model for intra-rater reliability (ICCA,1) and two-way random-effects, absolute-agreement model for inter-rater reliability, reported as average-measures (ICC2,2) and single-measures (ICC2,1). Bland-Altman 95% limits of agreement (LoA) and the minimal detectable change at the 95% confidence level (MDC95) were calculated. RESULTS: Eighty-five older adults (mean age [standard deviation], 76.1 [5.4] years; 86% women) were included after 13 of 98 recruited participants were excluded. Participants tended to overestimate their physical abilities (TUG: 6.0 [0.9] s; ITUG: 4.0 [1.4] s). Intra-rater reliability was moderate (ICCA,1, 0.69-0.73); simultaneous inter-rater reliability was excellent (ICC2,2 ≈ 0.994; ICC2,1, 0.982-0.984). Intra-rater MDC95 (2.3 s; 35.1%) exceeded inter-rater values (0.3 s; 4.9%), indicating within-session variability. Intra-rater 95% LoA were -2.65 to 1.85 s (EE) and -28.2% to 39.7% (Delta time); inter-rater LoA were -0.47 to 0.39 s and -5.8% to 7.6%. CONCLUSION: ITUG-derived EE shows moderate same-day intra-rater repeatability and excellent simultaneous inter-rater agreement, supporting further study of its clinical applicability.