The study titled “Impact of methods for data selection on the day-to-day reproducibility of resting metabolic rate assessed with four different metabolic carts” focuses on assessing resting metabolic rate (RMR) and respiratory exchange ratio (RER). RMR is crucial for clinicians and researchers, accounting for 60–70% of the 24-hour energy expenditure. Metabolic carts, which measure oxygen consumption (VO2) and carbon dioxide production (VCO2), are key in assessing RMR. However, the best method for selecting gas exchange data to compute an average value remains unclear, with various methods offering different RMR and RER estimations.

Study Goals

The study aims to (i) determine the influence of various methods for selecting indirect calorimetry data on RMR and RER assessments, and (ii) investigate how these methods affect the day-to-day reproducibility of RMR and RER.


The study involved 28 young, healthy adults, who underwent RMR assessments over two consecutive mornings using four different metabolic carts: Q-NRG, Vyntus CPX, Omnical, and Ultima CardiO2. Participants’ gas exchange was measured for 30 minutes with each cart, using three types of methods: short and long time intervals (TI), steady state (SSt), and methods filtering data by thresholding from the mean RMR. The study analyzed RMR and RER using these methods, along with their impact on day-to-day reproducibility.

Figure 1 illustrates the protocols employed in the study, which were consistently executed during both sessions, spaced 24 hours apart. In Panel A, the preliminary steps include recording the participants’ weight and height measurements. IC stands for indirect calorimetry. The term ‘Metabolic cart 1–4’ refers to the sequence of indirect calorimetry tests, each lasting 30 minutes, conducted with a variety of metabolic carts, namely the Q-NRG, the Vyntus, the Omnical, and the Ultima, utilized in no particular order. DXA represents the dual-energy X-ray absorptiometry scan. Measurements of weight, height, and DXA scans were taken only during the first visit.

Panel B presents examples of the different methodologies used for selecting gas exchange data. The top and bottom left panels illustrate the Time Interval (TI) methods, categorized into short and long durations, respectively. The top right panel demonstrates the 5-minute Steady State (SSt) method. The bottom right panel shows the medium filter method, where the two grey sections indicate the segments of data omitted by this filtering process. The yellow and blue lines trace the volume of oxygen uptake (VO2) and carbon dioxide output (VCO2), respectively. Consistent with established guidelines, the initial 5 minutes of data collection were excluded from analysis.

Omnical Metabolic Cart Results

RMR and RER Assessments:

RMR: The study found that using different methods for gas exchange data selection impacted the day-to-day reproducibility of RMR. Specifically, the 6–25 min and the 6–30 min long time interval (TI) methods yielded more reproducible RMR measurements when compared to other methods (short TI, steady state [SSt], and filtering methods).

RER: Similar to RMR, the reproducibility of RER measurements was also influenced by the method of gas exchange data selection. The 6–25 min and the 6–30 min long TI methods provided more consistent day-to-day RER values.

Impact on Day-to-day Reproducibility:

The study reported significant differences in day-to-day RMR reproducibility for the Omnical cart using different methods. The long TI methods (6–25 min and 6–30 min) showed lower absolute day-to-day RMR differences, indicating higher reproducibility.

For RER, the Omnical cart also demonstrated lower absolute day-to-day differences when using the 6–25 min and 6–30 min methods, suggesting these methods were more reliable for day-to-day RER assessments.

Coefficient of Variation (CV):

The CVs for both RMR and RER day-to-day differences were found to be within acceptable ranges when using the 6–25 min and 6–30 min methods. This indicates a high level of consistency in measurements over consecutive days.

Mean Bias and Limits of Agreement (LoA):

While the study did not mention specific values for mean bias and LoA for the Omnical cart, it was noted that the long TI methods showed narrower LoA and lower day-to-day CVs compared to other methods, implying a more consistent measurement performance.

For the Omnical metabolic cart, the study’s results emphasize the effectiveness of the 6–25 min and 6–30 min long time interval methods for assessing RMR and RER. These methods demonstrated superior day-to-day reproducibility and consistency, making them preferable for reliable metabolic rate assessments using this specific cart.

Figure 2 displays how different data selection methods for gas exchange impact the measurements of resting metabolic rate (RMR) and respiratory exchange ratio (RER) across various metabolic carts during the initial visit. In the graph:

  • Black bars show results from short TI methods.
  • Light grey bars are for long TI methods.
  • White bars denote SSt periods.
  • Dark grey bars indicate results from filtering methods.

Statistically significant differences, marked in bold, were determined through ANOVA (n=28) and post-hoc Bonferroni tests. Data include mean and SD values. “Vyntus” refers to the Vyntus CPX cart, and “Ultima” to the Ultima CardiO2 cart, with minute-by-minute tracking of oxygen consumption (VO2) and carbon dioxide production (VCO2).


The study concludes that the 6–25 min and 6–30 min long time interval methods should be preferred for selecting data in RMR and RER assessments using metabolic carts. These methods resulted in the highest day-to-day reproducibility and were better associated with classical RMR predictors. The findings are significant as they were replicated across four different indirect calorimetry systems, adding important insights to the current guidelines for assessing RMR in healthy and non-ventilated patients.

Related products


The Omnical is the most versatile and accurate indirect calorimeter for research purposes on the market. Comprised of state-of-the-art technology using the highest-class precision measurement instruments, it enables customers to perform studies in various research fields. The system is designed to measure energy metabolism ranging from resting metabolism rate (RMR) to sports performance testing (e.g. VO2max tests) with high accuracy.

How can we help you with your research?

Maastricht Instruments creates equipment in the field for indirect calorimetry measurements. We provide support for studies, research and measurements alongside our indirect calorimetry products. Consult us about our indirect calorimetry metabolic  cart,  whole room calorimeter  systems or  accelerometry  add-ons. Please  contact us or find more information on our information pages.


J.M.A. Alcantara, L. Jurado-Fasoli, M. Dote-Montero, E. Merchan-Ramirez, F.J. Amaro-Gahete, I. Labayen, J.R. Ruiz, G. Sanchez-Delgado, Impact of methods for data selection on the day-to-day reproducibility of resting metabolic rate assessed with four different metabolic carts, Nutrition, Metabolism and Cardiovascular Diseases, Volume 33, Issue 11, 2023, Pages 2179-2188, ISSN 0939-4753,