Validity and Reliability of the 6-Minute Step Test in Healthy Individuals: A Cross-sectional Study

Abstract

Objective: To determine the 6-minute step test's (6MST) reliability and validity and to establish reference performance values of this test.

Design: Prospective observational cross-sectional study.

Setting: Spirometry and Respiratory Physiotherapy Laboratory, Federal University of São Carlos (institutional).

Participants: Ninety-one individuals [42 men and 49 women, mean age = 39 years (SD, 17 years)] without any diagnosed diseases and with normal exercise capacity [6-minute walk test (6MWT) >75% of the predicted normal].

Independent variables: Participants underwent two 6MST on 1 day and two 6MWT on another day in randomized order. Furthermore, age, gender, height, weight, lower limbs length, abdominal circumference, percentage of body fat, and fat-free mass were obtained.

Main outcome measures: Test-retest reliability was assessed by comparing the findings of the two 6MST using the intraclass correlation coefficient (ICC) and Bland-Altman plot. Validity was assessed by comparing outcomes of the 6MST to outcomes of 6MWT using the Pearson correlation coefficient. A multiple regression analysis was conducted using the stepwise method to develop an equation to predict reference values.

Results: The performance (mean steps ± SD) in the first and second test was 149 ± 34 and 149 ± 36 steps, respectively, which was correlated to distance (in meters) in 6MWT (r = 0.72; P < 0.05). Six-minute step test performance was reliable (ICC = 0.9; 95% confidence interval: 0.85-0.93). The equation to predict reference values for the first 6MST was significant (P < 0.001 and R = 0.48): Performance(steps) = 174 to 1.05 × Age(years) to women and Performance(steps) = 209 to 1.05 × Age(years) to men.

Conclusions: Six-minute step test is a reliable and valid test. Moreover, the number of steps may be predicted by demographic and anthropometric variables with moderate strength of prediction.

Clinical relevance: Six-minute step test is an exercise test that is easy to be conducted, more tolerable than a graded exercise test, requires fewer equipments and space, and permits better monitoring of the participants. The assessment of the reliability, validity, and reference values will provide a better interpretability for clinicians to use it, especially in primary care.