Agreement Between Six-Minute Walk Test-Based Equations and Bruce-Derived Aerobic-Fitness Estimates in Adults with Metabolic Syndrome: A Single-City Cross-Sectional Method-Comparison Study

Abstract

Accessible assessment of aerobic fitness is important for adults with metabolic syndrome when cardiopulmonary exercise testing is unavailable. This study aimed to evaluate participant-level agreement between Six-Minute Walk Test (6MWT)-based equations and estimates derived from total Bruce treadmill duration. Using a single-city cross-sectional method-comparison design, 105 newly recruited adults, comprising 67 women and 38 men, completed standardized 6MWT and graded treadmill assessments. Agreement was evaluated using mean bias, mean absolute error (MAE), root mean square error (RMSE), Pearson correlation, calibration, proportional-bias regression, and Bland–Altman limits of agreement. Mean Bruce-derived estimated peak oxygen uptake (VO2peak) was 23.42±1.87 mL·kg−1·min−1. Model 1 produced 15.90±1.72, with a mean bias of −7.53, an RMSE of 7.77, and limits of agreement from −11.29 to −3.76. Model 3 produced 16.78±3.28, with a mean bias of −6.65, an RMSE of 7.11, and limits from −11.60 to −1.70. Both models systematically underestimated Bruce-derived values, and Model 3 showed proportional bias. Model 2 produced 99.31±4.82% on its original age- and sex-adjusted percentage-predicted scale. It was not converted to mass-specific units because the participant-specific reference values required for a valid back-conversion were unavailable. The observed bias and limits of agreement indicated that Models 1 and 3 did not achieve close participant-level agreement with the Bruce-derived approach. Validation against directly measured oxygen uptake remains necessary before clinical or public-health use.