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Measurement properties of the SARC-T: test-retest reliability, agreement and minimal detectable change in older
Blanca Pedauyé-Rueda1,2, José Luis Maté-Muñoz3, Juan Hernández-Lougedo1,2
1HM Faculty of Health Sciences, Camilo José Cela University, Madrid, Spain.
Background:
The Sarcopenia Optoelectronic Chair-Rise Velocity Test (SARC-T) has been proposed as an instrumented chair-rise measure related to physical function in sarcopenia; however, its test-retest measurement properties have not been established. This study evaluated the test-retest reliability, agreement, measurement error and minimal detectable change at the 95% confidence level (MDC95) of the SARC-T in older adults with sarcopenia.
Methods:
An observational methodological test-retest study was conducted in 55 institutionalized older adults with sarcopenia diagnosed according to EWGSOP2 criteria. The SARC-T was assessed in two sessions separated by 5 days under standardized conditions. The primary outcome was the best mean propulsive velocity recorded during the concentric phase. Test-retest reliability was assessed using ICC (3,1), Lin's concordance correlation coefficient (CCC), standard error of measurement (SEM), MDC95, Bland-Altman analysis, and a linear mixed-effects model.
Results:
Test-retest reliability was high (ICC = 0.93, 95% CI 0.88-0.96; CCC = 0.93, 95% CI 0.86-0.96). Measurement error was low (SEM = 0.017 m/s), and MDC95 was 0.05 m/s. Bland-Altman analysis showed a small but statistically significant mean bias of +0.008 m/s (p = 0.015), with 95% limits of agreement from -0.042 to +0.058 m/s, and additional analysis showed statistically significant proportional bias (slope = 0.161; p = 0.009). A small systematic session effect was also observed in the mixed-effects model (β = +0.008 m/s; 95% CI 0.002-0.018; p = 0.012).
Conclusion:
Under the standardized conditions of the present protocol, the SARC-T showed high test-retest reliability and low measurement error; however, the presence of statistically significant mean and proportional bias indicates that agreement is not fully uniform across the measurement range and should be interpreted with caution, particularly at the individual level. The MDC95 may help interpret whether longitudinal changes in mean propulsive velocity are likely to exceed measurement-related fluctuation. These findings should be considered within the context of this specific population of institutionalized older adults with sarcopenia.
