100 Oxygen consumption per kg of body weight or metabolic equivalent (MET)

Oxygen consumption per kg and METs: definition, activity intensity and fitness as a predictor of mortality.

Oxygen consumption per kilogram of body weight makes oxygen use comparable between people of different size. It is the basis of the metabolic equivalent (MET): 1 MET is the oxygen consumption at quiet rest, conventionally 3.5 mL O₂/kg/min, which corresponds to roughly 1 kcal/kg/h. The intensity of any activity can be expressed as a multiple of this resting value, and the maximal MET level reached on a stress test describes a person's functional capacity. In this application the value is linked to the activity of triiodothyronine, the thyroid hormone that sets the metabolic rate of tissues such as the heart, gastric mucosa, liver, kidneys and smooth muscles.

MetabolismPhysical fitnessMETs

1 MET3.5 mL O₂/kg/min

Walking≈ 3–4 METs

Running≈ 8–12 METs

Each +1 MET of fitness≈ 13% lower all-cause mortality

Figure 1. Cardiorespiratory fitness categories by peak METs (Kodama et al., 2009). Low fitness was associated with a 70% higher risk of death than high fitness.

Why fitness matters

In a meta-analysis of 33 studies with more than 100 000 participants, every 1-MET higher level of cardiorespiratory fitness was associated with about a 13% lower risk of death from any cause and a 15% lower risk of cardiovascular events. Fitness can be improved at any age by regular aerobic exercise.

Interpretation

Low exercise capacity (for example below about 5 METs) is associated with a worse prognosis in heart and lung disease and with higher surgical risk
Resting oxygen consumption per kilogram is higher in children, with fever and hyperthyroidism, and lower in older people, with hypothyroidism and obesity (fat tissue uses little oxygen)
The conventional 3.5 mL/kg/min may overestimate the true resting value in older or obese people

Why it matters

Adults are recommended to do at least 150 minutes of moderate (3–6 METs) or 75 minutes of vigorous (above 6 METs) activity a week.

References

Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990;13(8):555–565. doi:10.1002/clc.4960130809
Kodama S, Saito K, Tanaka S, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024–2035. doi:10.1001/jama.2009.681
Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020;54(24):1451–1462. doi:10.1136/bjsports-2020-102955

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 6 May 2024