Active Voice: Re-thinking the Universal Assumption of the MET By Robert G. McMurray, Ph.D., Fellow Emeritus ACSM Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM. Robert McMurray, Ph.D., FACSM, is the Smith-Gunter Distinguished Professor Emeritus of Exercise and Sport Science and Nutrition at the University of North Carolina at Chapel Hill, NC. His research has focused on issues relating exercise and metabolism to obesity and the development of cardiometabolic risk factors in children and adults. He received the ACSM Citation Award in 2011 in recognition for his contributions to the field. This commentary presents Dr. McMurray’s views on the topic of a research article which he and his colleagues published in the June 2014 issue of Medicine and Science in Sports and Exercise® (MSSE). We in the exercise community tend to overlook the importance of resting metabolic rate (RMR), even though it accounts for most of the daily energy expenditure of a typical adult. RMR is relevant to public health efforts intended to thwart the growing obesity and diabetes epidemics, which target groups of older and/or overweight adults for the delivery of physical activity programs. Estimates of RMR are used frequently to infer energy costs of participation in physical activity and to estimate daily energy expenditure as applied to achieving energy balance. This typically occurs via the use of the metric, the “MET,” or metabolic equivalent. To examine this issue more closely, we conducted a review and meta-analysis of previous research on RMR, using studies dating as far back as the 1920s. We reported on the results of this research in our recent article published in MSSE. Our overall finding was that, compared to the standard MET, the mean RMR typically is lower by approximately 10% for men, 15% for women, >20% for adults with BMI ≥ 30 kg.m-2 (i.e., obese), and ~25% for older adults. Also, mean RMR may be as much as 20-30% lower for combinations of these demographic and BMI groups. We concluded that no single RMR value is appropriate for all adults. Furthermore, the nearly universally accepted MET convention seems to apply almost exclusively to young, lean men, who are not representative of the typical American adult. These errors in RMR could impact public policy because the 2008 U.S. Physical Activity Guidelines are based on MET-minutes/week. Byrne and colleagues previously have shown that the conventionally-defined MET value often overestimates RMR and does not apply well to all individuals, nor to population subgroups. The yet-to-be-published review paper in MSSE by Hall et al. on older adults clearly acknowledges that the present conventional value for RMR also is unsuitable for the elderly, introducing errors when the standard MET is used to calculate energy expenditure for activities. In addition, Ainsworth et al., in their Compendium of Physical Activities, note that while their value for the MET is not absolute for all persons, the MET can still be used for estimating the intensity of physical activity for epidemiological studies. In spite of that, more and more studies are using the MET as an absolute value and applying it in situations beyond its capabilities. Because of existing public health efforts to address things like the obesity and diabetes epidemics, having better estimations of RMR, particularly for groups of women, older adults, and the obese may help better to plan and achieve intervention outcomes. Given the known errors in estimating RMR, and their expanded use in many contexts, one must carefully consider the longstanding adherence to using the conventional MET value for RMR.