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1 School of Human Movement Studies, Queensland University of Technology, Brisbane, Queensland, Australia; Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama, USA
2 School of Human Movement Studies, Queensland University of Technology, Brisbane, Queensland, Australia
3 Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama, USA; Department of Human Studies, Univeristy of Alabama at Birmingham, Birmingham, Alabama, USA
4 Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama, USA
5 Institute of Physiology, University of Lausanne, Lausanne, Switzerland
* To whom correspondence should be addressed. E-mail: n.byrme{at}qut.edu.au.
The metabolic equivalent (MET) is a widely used physiological concept that represents a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate (RMR). The value equating 1-MET (3.5 mlO2/kg/min or 1 kcal/kg/hr) was first derived from the resting oxygen consumption of one person, a 70kg, 40-year-old man. Given the extensive use of MET levels to quantify physical activity level or work output, we investigated the adequacy of this scientific convention. Subjects consisted of 642 females and 127 males, 18-74 years of age, 35-186kg, who were weight-stable and healthy albeit obese in some cases. RMR was measured by indirect calorimetry using a ventilated hood system, and the energy cost of walking on a treadmill at 5.6 kph was measured in a subsample of 49 males and 49 females (26 - 45 kg/m2; 29 - 47 years). Average VO2 and energy cost corresponding with rest (2.6 ± 0.4 mlO2/kg/min and 0.84 ± 0.16 kcal/kg/h respectively) were significantly lower than the commonly accepted 1-MET values of 3.5 mlO2/kg/min and 1 kcal/kg/h respectively. Body composition (fat mass and fat-free mass) accounted for 62% of the variance in resting VO2, compared with age which accounted for only 14%. For a large heterogeneous sample, the 1-MET value of 3.5 ml/kg/min overestimates the actual resting VO2 value on average by 35% and the 1-MET of 1 kcal/hr overestimates resting energy expenditure by 20%. Using measured or predicted RMR (ml O2/kg/min or kcal/kg/h) as a correction factor can appropriately adjust for individual differences when estimating the energy cost of moderate intensity walking (5.6 kph).
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