The six-minute step test as a predictor of cardiorespiratory fitness in obese women

Abstract

Background: The impaired cardiorespiratory fitness (CRF) status is a hallmark in obese individuals, especially in women around the world. Some field tests have been proposed to evaluate functional capacity in this population. The Six-Minute Step Test (6MST) could be a feasible alternative to cardiopulmonary exercise testing (CPX) if the resources and space are limited. However, an optimal performance cutoff using the 6MST as well as predictive equations of metabolic and cardiovascular responses to CPX from 6MST data have to not been established.

Aim: To assess the 6MST accuracy to determinate CRF and its ability to predict peak oxygen consumption (VO2) and heart rate (HR) achieved during CPX in sedentary obese women.

Design: Observational and cross-sectional study.

Setting: The study was performed at a Physiotherapy Department of a public University and enrolled individuals from the community.

Population: Fifty-six obese women (35±7 years old).

Methods: Subjects underwent a clinical evaluation, CPX, and the 6MST. We applied Bland-Altman plots to assess concurrent validity between exercise tests regarding peak VO2 and HR. Receiver operating characteristic curve analysis and stepwise multiple linear regression analysis assessed the predictive accuracy of the 6MST; specifically the ability to predict peak VO2 and HR achieved during CPX. Significance level was P<0.05.

Results: There was a satisfactory concurrent validity between the CPX and 6MST, with a mean difference of 5.1±3.6 mL·kg-1·min-1 and 23±13 bpm in relation to peak VO2 and HR, respectively. The 6MST demonstrated moderate accuracy in predicting CPX responses (area under the curve: 0.72, 95% CI: 0.59-0.83). The number of step cycles and peak HR during the 6MST explained 31% and 39% of the total variance in peak VO2 and HR obtained during CPX, respectively.

Conclusion: The 6MST is accurate to discriminate obese women with an adequate CRF from women with a poor status and it can predict metabolic and cardiovascular maximal exercise values.

Clinical rehabilitation impact: Our findings indicate the 6MST is a simple and inexpensive functional evaluation tool and may be a valid means of assessing CRF in sedentary obese women, particularly in clinical settings where space and resources are limited.