Estimation and performance evaluation of Speed-to-MET conversion methods using the 6-Minute Walk Distance

Metabolic Equivalent of Task (MET) is a key measure of exercise intensity and a patient's functional capacity. In clinical practice, MET is typically derived from direct measurements of oxygen consumption (VO₂) or estimated using formulas based on walking speed. The 6-Minute Walk Distance (6MWD) is one of the most commonly used submaximal tests for assessing functional capacity; however, no rigorously developed model currently allows precise estimation of MET based solely on this test. The aim of this study was to evaluate commonly used formulas and to develop a model enabling estimation of MET from the distance covered during the 6MWD. We analyzed established formulas recommended by the American College of Sports Medicine (ACSM) as well as simplified relationships applied in the 6MWD. Based on empirical VO₂ data, we proposed a regression model that accounts for the nonlinear relationship between walking distance and energy expenditure, combining mathematical optimization with physiological plausibility. Using this approach, we developed a practical conversion table of MET values for distances typical of the 6MWD (100-800 meters). The existing estimation formulas demonstrated limited applicability in clinical populations, particularly at higher distances. In contrast, the proposed nonlinear model captures the distance-MET relationship and enables assignment of MET values based on 6MWD results without the need for treadmill testing or respiratory gas analysis. This tool can support the qualification of patients for rehabilitation and enable more precise planning of individualized training recommendations in clinical settings, contributing to improved clinical decision-making and comparability across studies.