Metabolic equivalent: one size does not fit all.
Level 4 - case-series / case-control
Cross-sectional physiological study
PubMed 15831804 · doi:10.1152/japplphysiol.00023.2004
What was done
Indirect calorimetry via a ventilated hood system was used to measure resting metabolic rate (RMR) in 769 healthy, weight-stable adults (642 women, 127 men; age 18–74 years; body weight 35–186 kg). In a subsample of 98 participants (49 men, 49 women; BMI 26–45 kg/m²; age 29–47 years), the energy cost of treadmill walking at 5.6 km/h was also measured to test the accuracy of the conventional 1-MET standard (3.5 ml O2·kg⁻¹·min⁻¹ or 1 kcal·kg⁻¹·h⁻¹).
What was found
Average resting VO2 was 2.6 ± 0.4 ml O2·kg⁻¹·min⁻¹ and resting energy expenditure was 0.84 ± 0.16 kcal·kg⁻¹·h⁻¹, both significantly lower than the standard 1-MET values. The accepted 1-MET value overestimated actual resting VO2 by an average of 35% and resting energy expenditure by 20%. Body composition (fat mass and fat-free mass) accounted for 62% of the variance in resting VO2, compared with 14% for age. Applying measured or predicted RMR appropriately adjusted for individual differences during moderate walking.
Why it matters
The widely accepted 1-MET convention substantially overestimates baseline energy expenditure, meaning standard equations miscalculate the energy cost of physical activity across diverse populations.
Limits
The study sample was predominantly female (83%), and the physical activity trial was restricted to a single walking speed in an overweight/obese subsample (BMI 26–45 kg/m²), limiting direct generalizability to other exercise intensities, modalities, and normal-weight individuals.
Cited by
- supports One metabolic equivalent (MET) is defined as the resting oxygen consumption of 3.5 mL of oxygen per minute per kilogram of body mass.