Characteristics of Systematic Errors in the Two-step Test for Assessing Locomotive Syndrome among Young and Older Adults.

Abstract

Objectives: The two-step test is a key component of the locomotive syndrome risk test, but few studies have examined its systematic errors, particularly in young adults. We investigated errors in young and older adults and identified the threshold for measurement errors.

Methods: This cross-sectional study included 95 university students and 40 older adults and was conducted between April 2023 and March 2025. Participants performed the two-step test twice within a 7-day interval. Bland-Altman analysis assessed fixed and proportional bias for the two-step test length (length) and value (length normalized to height), and minimal detectable change (MDC) and limit of agreement (LOA) were calculated.

Results: In young adults, the two-step test length was 279.2 ± 24.4 cm (difference: 8.4 ± 12.3 cm) and the two-step test value was 1.70 ± 0.11 cm/height (difference: 0.05 ± 0.07 cm/height); in older adults, these respective results were 140.7 ± 34.3 cm (0.0 ± 13.7 cm) and 0.89 ± 0.21 cm/height (0.00 ± 0.09 cm/height). In young adults, fixed bias was identified for length and value, whereas no systematic errors were detected in older adults. LOA ranged from -11.5 to 28.2 cm for length and from -0.07 to 0.17 cm/height for value in young adults. The MDC in older adults was 26.9 cm for length and 0.17 cm/height for value.

Conclusions: In young adults, the result for the two-step test tended to increase during retesting, requiring caution in interpreting intervention effects. An increase at retesting of more than 0.17 cm/height for the test value or 25-30 cm for test length may be a clinically useful indicator, exceeding the smallest detectable change for both young and older adults based on LOA and MDC.