Article

Metabolic equivalent: One size does not fit all

School of Human Movement Studies, Queensland Univ. of Technology, Victoria Park Rd., Kelvin Grove, Q4059, Brisbane, Queensland, Australia.
Journal of Applied Physiology (Impact Factor: 3.43). 10/2005; 99(3):1112-9. DOI: 10.1152/japplphysiol.00023.2004
Source: PubMed

ABSTRACT 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 ml O2 x kg(-1) x min(-1) or 1 kcal x kg(-1) x h(-1)) was first derived from the resting O2 consumption (VO2) of one person, a 70-kg, 40-yr-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 women and 127 men, 18-74 yr of age, 35-186 kg in weight, 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 km/h was measured in a subsample of 49 men and 49 women (26-45 kg/m2; 29-47 yr). Average VO2 and energy cost corresponding with rest (2.6 +/- 0.4 ml O2 x kg(-1) x min(-1) and 0.84 +/- 0.16 kcal x kg(-1) x h(-1), respectively) were significantly lower than the commonly accepted 1-MET values of 3.5 ml O2 x kg(-1) x min(-1) and 1 kcal x kg(-1) x h(-1), 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 O2 x kg(-1) x min(-1) overestimates the actual resting VO2 value on average by 35%, and the 1-MET of 1 kcal/h overestimates resting energy expenditure by 20%. Using measured or predicted RMR (ml O2 x kg(-1) x min(-1) or kcal x kg(-1) x h(-1)) as a correction factor can appropriately adjust for individual differences when estimating the energy cost of moderate intensity walking (5.6 km/h).

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    • "Les équivalences en MET sont des approximations, et il est évident que la congruence en (1) n'a pas la prétention de remplacer une mesure du métabolisme de base, ni son estimation à partir d'équations dédiées [24] [25]. En effet, appliquée strictement , elle conduit à une surestimation [26] surtout marquée chez les femmes et les personnes âgées qui présentent en moyenne une masse maigre réduite par rapport aux hommes et aux jeunes adultes. La principale raison est qu'elle ne se réfère qu'à la masse et que les facteurs âge, taille et sexe ne sont pas utilisés pour moduler l'évaluation (sauf dans certaines études où on utilise 0,95 kcal/kg/h chez la femme au lieu de (1)). "
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    • "The direct method often converts the measures into metabolic equivalent of tasks (METs) that are widely accepted notion in energy expenditure of physical activity. It is commonly viewed as a measure that could provide a common descriptor of workload levels across populations (Byrne et al, 2005). Due to its optimal accuracy, the use of METs is commonly preferred to determine the level of physical activity (Ainsworth, 2009; Ainsworth et al, 2011). "
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    • "It is noteworthy that absolute energy costs of any particular activity depend on an individual basal energy expenditure, age, sex, size, skill and level of fitness (WCRF/AICR, 2007). The MET scores in the Compendium were calculated considering of healthy 40 year old males with the average body mass of 70 kg, and may not correspond to absolute energy expenditure for females (Byrne et al., 2005). However, MET-scores are valid and useful when the relative energy expenditure is compared within populations (Ainsworth et al., 1993; Friedenreich et al., 1998). "
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