Estimating endurance training intensity prescription from the 6-minute stepper test in people with chronic obstructive pulmonary disease - a multicenter cross-sectional study with external validation

Abstract

Background: Home-based pulmonary rehabilitation (PR) can enhance accessibility to PR, but no at-home field exercise test has been validated for individualized endurance training prescriptions.

Research question: What is the accuracy of the six-minute stepper test (6MST) in estimating endurance training intensity as determined during cardiopulmonary exercise testing (CPET)?

Study design and method: This multicenter (N = 3) cross-sectional study included individuals with COPD. Participants performed CPET and two 6MSTs to evaluate the 6MST's ability to estimate endurance training intensity based on CPET-derived heart rate at the first ventilatory threshold (HRvt₁), the corresponding power output (Pvt₁), and peak power output (Ppeak). Predictive equations were tested for external validity using data from two prior studies.

Results: 105 patients were included (mean age 61 (SD 9) years; mean FEV1 61 (SD 21) %). Predictive equations moderately predicted HRvt₁ (r² = 0.38), strongly predicted Pvt₁ (r² = 0.63) and very strongly predicted Ppeak (r² = 0.75). External validity was small to moderate for HRvt₁ and Pvt₁ but was strong for 60% of Ppeak (mean absolute difference: 10W, 95% CI 5 to 10). Passing and Bablok regression confirmed interchangeability for Pvt₁ and 60% of Ppeak.

Interpretation: The 6MST offers a reliable method to set initial training intensity when CPET is unavailable.

Clinical trial registration: NCT02842463.

Keywords: Chronic obstructive pulmonary disease; cardiopulmonary exercise testing; exercise test; pulmonary rehabilitation; six-minute stepper test.