Giacomantonio, N, Morrison, P, Rasmussen, R, and MacKay-Lyons, MJ. Reliability and validity of the 6-minute step test for clinical assessment of cardiorespiratory fitness in people at risk of cardiovascular disease. J Strength Cond Res 34(5): 1376-1382, 2020-The purpose of this study was to determine the test-retest reliability and validity of the 6-minute step test (6MST) as a potential assessment of cardiorespiratory fitness (CRF) of people at risk of cardiovascular disease (CVD). A prospective, cross-sectional, correlational study design was used. A single cohort of 30 adults with 2 or more risk factors for CVD was recruited. Exercise tests were scheduled on 2 days, separated by 1 week. Validity was determined by comparing 6MST results with those obtained in a symptom-limited treadmill test and the 6-minute walk test (6MWT). Main outcome variables were peak heart rate (HRpeak) and peak oxygen consumption (V[Combining Dot Above]O2peak) measured during the 6MST, treadmill test, and 6MWT. Test-retest reliability of HRpeak and V[Combining Dot Above]O2peak during the 6MST was very strong (intraclass correlation coefficient [ICC], 0.92; 95% confidence interval [CI], 0.83-0.97 and ICC, 0.93; 95% CI, 0.84-0.97, respectively). Correlations were also very strong between 6MST and treadmill test HRpeak (r = 0.81) and between 6MST and treadmill test V[Combining Dot Above]O2peak (r = 0.88). Correlations were moderate between 6MST HRpeak and 6MWT steady-state HR (r = 0.57) and strong between 6MST V[Combining Dot Above]O2peak and 6MWT steady-state V[Combining Dot Above]O2 (r = 0.70). The 6MST seems to be a reliable, valid option for assessing CRF of people at risk of CVD in a broad range of clinical settings. Providing practical, accessible tests will help facilitate the goal of establishing CRF as a clinical vital sign. The next step in the development of the 6MST should be to identify the most appropriate 6MST predictor variables to estimate V[Combining Dot Above]O2max.