Feasibility, Test-Retest Reliability and Convergent Validity of the Two-Minute Step Test in Older Adults With Intellectual Disabilities

BACKGROUND: Cardiorespiratory fitness is a crucial component for health. However, measuring cardiorespiratory fitness in older adults with intellectual disabilities (ID) in practice and in large-scale studies remains challenging. The Two-Minute Step Test (2MST) is a submaximal cardiorespiratory fitness test that is brief, relatively easy to perform, and does not require any expensive materials. However, the clinimetric properties of the 2MST for older adults with ID are unknown. Therefore, this study aimed to determine the feasibility, reliability and convergent validity of the 2MST in older adults with ID.

METHOD: This was a cross-sectional study within the 'Healthy Ageing and Intellectual Disabilities' (HA-ID) cohort study. Participants (n = 180, 70.6 [66-75] years) that participated in the physical fitness assessment were included in this study. Feasibility was defined as a successful completion according to protocol. Test-retest reliability was assessed over two measurements, on the same day, with the intraclass correlation coefficient (ICC). Convergent validity was assessed relative to other fitness components (static balance, muscular endurance, comfortable and fast gait speed), with Pearson's and Spearman's correlation coefficients.

RESULTS: The 2MST showed moderate feasibility for the first (49.4%) and second (48.3%) measurement. Feasibility was good in participants with borderline, mild and moderate ID (57.1%-80%), but low in participants with severe (15.2%) and profound ID (7.7%). Test-retest reliability was excellent (ICC = 0.88). The 2MST had a moderate correlation with static balance (r = 0.46) and comfortable (r = 0.42) and fast (r = 0.51) gait speed, and a good correlation with muscular endurance (r = 0.63). Based on predefined criteria, all correlations were at least moderate (r > 0.30), supporting good convergent validity (categorised as good if three or more out of four correlations were at least moderate).

CONCLUSIONS: The 2MST is a feasible, reliable and valid test to use in older adults with ID. Feasibility was especially good in older adults with borderline to moderate ID; however, it was low in adults with more severe ID. The excellent test-retest reliability and good indications for convergent validity show this test is a suitable field test for cardiorespiratory fitness to use in older adults with ID.