Accuracy of metabolic equivalents (METS) for aerobic exercise prescription from estimated and measured 1-MET values in healthy men

Abstract

Introduction: Multiples of the metabolic equivalent (MET) are widely used to prescribe exercise intensity and quantify the energy cost of physical activities. A growing body of empirical evidence, however, suggests the standardized 1-MET value, represented by a resting oxygen uptake (VO2) of 3.5 mL·kg-1·min-1, significantly overestimates observed resting VO2 in populations with lower cardiorespiratory fitness (CRF). Objective: Compare the standardized MET and resting VO2 with respect to these two applications and explore the association between CRF and resting VO2. Methods: A heterogeneous cohort of 114 healthy men, aged 18 to 38 yr, volunteered to participate in two studies. First, 100 men [lower CRF: n = 48, VO2max < 50.0 mL∙kg-1∙min-1; higher CRF: n = 52, VO2max ≥ 50.0 mL∙kg-1∙min-1] visited the laboratory twice to explore the association between directly assessed VO2max and resting VO2. Second, 14 men performed a 30-min bout of running at 8.0 km∙h-1 (8.3 METs according to the Compendium of Physical Activities) to investigate the use of the MET to quantify the energy cost of treadmill running. Results: The VO2max was positively correlated with resting VO2 (R = 0.68, P < 0.001). The mean observed resting VO2 values of 3.28 (n = 100) and 3.07 (n = 14) mL·kg-1·min-1 were significantly lower than the standardized value of 3.5 mL·kg-1·min-1 (P < 0.001 and P = 0.005, respectively). When compared to the standardized value, groups with lower CRF demonstrated significantly lower mean observed resting VO2 values of 3.06 (1st part of the study: P < 0.001) and 2.67 (2nd part of the study, P < 0.001) mL·kg-1·min-1. However, no significant difference was observed between standardized and observed resting VO2 values for the groups with higher CRF (1st part of the study: P = 0.87; 2nd part of the study: P = 0.78). Hence the observed values for METmax intensity and the energy cost of treadmill running were significantly underestimated when calculated using the standardized resting VO2 value of 3.5 mL·kg-1·min-1 (P = 0.005 to P < 0.001) only for the groups with lower CRF. Conclusion: The standardized MET value considerably overestimated observed resting VO2 in men with lower CRF. Direct determination of resting VO2 is therefore preferred to improve the accuracy of the aforementioned applications in this population.