Alcantara et al. (2022) wanted to research how accurate, precise, within-subject repeatability, and concordance of RMR and RER could be assessed using four commercially metabolic carts.

The energy required to maintain normal physiological function in an awake person resting in thermoneutrality is known as the resting metabolic rate (RMR). The reference method for determining human RMR is indirect calorimetry, which measures oxygen consumption (VO2) and carbon dioxide generation (VCO2). Indirect calorimetry can also be used to calculate the respiratory exchange ratio (RER), which tells you how many macronutrients are being oxidized. In clinical and research settings, metabolic carts are the most utilized indirect calorimeters for determining RMR and RER. The Deltatrac (DTC; Datex Instrumentarium Corp, Helsinki, Finland), a popular metabolic cart, has long been regarded as the gold standard for determining RMR and RER in humans. The DTC, however, is no longer produced, and no other metabolic cart has yet been identified as the ideal replacement instrument.

The validity of a metabolic cart can be determined by (i) using controlled pure gas infusions [nitrogen (N2) and CO2] to assess its accuracy and precision; (ii) using alcohol burning tests to assess its accuracy and precision; and (iii) assessing the within-subject reproducibility (i.e. the variability in repeated measures performed in individuals under the same conditions, thereinafter called reproducibility). There is no published validity evidence for RMR and RER for many commercially available metabolic carts, and some metabolic carts have produced inadequate accuracy, precision, and/or reproducibility. It’s worth noting that most studies comparing the accuracy and precision of different metabolic carts haven’t done so in the same settings and situations, or haven’t used new built metabolic carts.

Goal of the study

The goal of this study was to compare the accuracy, precision, reproducibility, and concordance of RMR and RER assessments provided by four commercially available metabolic carts: the Q-NRG (Cosmed, Rome, Italy), the Vyntus CPX (Vyaire, Höchberg, Germany; hereinafter referred to as Vyntus), the Omnical (Maastricht Instruments, Maastricht, The Netherlands), and the Ultima CardiO2 (M (Medgraphics Corporation, St. Paul, MN, USA; thereinafter called Ultima). We also looked at how the ICcE affects the RMR and RER evaluations’ repeatability and concordance.


On five non-consecutive days, three studies were undertaken to simulate varied RMR and RER using controlled pure gas (N2 and CO2) infusions. Furthermore, three non-consecutive days of 30-minute methanol burns were performed. Finally, the RMR and RER of 29 young non-ventilated individuals (11 women; 25–4 years old; BMI: 24.1–3.2 kg/m2) were measured twice under standardized settings, 24 hours apart, using each instrument.


The study found that the four metabolic carts provided inconsistent RMR and RER values. Overall, the Omnical delivered more accurate and exact RMR and RER calculations than the Q-NRG, Vyntus, and Ultima CardiO2, and may be the best tool for determining RMR and RER in non-ventilated humans.

How can we support your research?

Maastricht Instruments has developed indirect calorimetry measurement equipment. You can contact us for product and software support, measurement methods and protocols, validation procedures, data processing and interpretation, and other technological requirements for your project in addition to our indirect calorimetry solutions.

Please contact us if you have any questions concerning our indirect calorimetry metabolic cart, whole-body room calorimeter systems, or accelerometry add-ons.


J.M.A. Alcantara, J.E. Galgani, L. Jurado-Fasoli, M. Dote-Montero, E. Merchan-Ramirez, E. Ravussin, J.R. Ruiz, G. Sanchez-Delgado, Validity of four commercially available metabolic carts for assessing resting metabolic rate and respiratory exchange ratio in non-ventilated humans, Clinical Nutrition, Volume 41, Issue 3, 2022, Pages 746-754, ISSN 0261-5614,

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The Omnical is the market’s most versatile and accurate indirect calorimeter for research. It allows users to conduct investigations in a variety of study sectors using cutting-edge technology and top-of-the-line precision measurement devices. The system is designed to monitor energy metabolism with great precision, ranging from resting metabolic rate (RMR) through sports performance testing (e.g. VO2max tests).

Omnical RMR / BMR

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