Whole-room indirect calorimeters (WRICs) have traditionally been used for real-time resting metabolic rate (RMR) measurements, while metabolic rate (MR) during short-interval exercises has commonly been measured by metabolic carts (MCs). This study aims to investigate the feasibility of incorporating short-interval exercises into WRIC study protocols by comparing the performance of WRICs and an MC. We assessed the 40-min RMR of 15 subjects with 2-day repeats and the 10-15 min activity MR (AMR) of 14 subjects at three intensities, using a large WRIC, a small WRIC, and an MC. We evaluated the biases between the instruments and quantified sources of variation using variance component analysis. All three instruments showed good agreement for both RMR (maximum bias = 0.07 kcal/ min) and AMR assessment (maximum bias = 0.53 kcal/min). Moreover, the majority of the variability was between-subject and between-intensity variation, whereas the types of instrument contributed only a small amount to total variation in RMR (2%) and AMR (0.2%) data. In Conclusion, the good reproducibility among the instruments indicates that they may be used interchangeably in welldesigned studies. Overall, WRICs can serve as an accurate and versatile means of assessing MR, capable of integrating RMR and short-interval AMR assessments into a single protocol. Whole-room indirect calorimeters (WRICs) have been used to assess various metabolic states in both healthy subjects and subjects affected by pathologies 1,2. A WRIC, an isolated room with a known volume and a controlled air inflow rate, provides minute-by-minute measurements of the subject's O 2 consumption and CO 2 production from breaths, via the continuous measurement of O 2 and CO 2 concentrations in inflow air and outflow air. These data enable precise calculations of metabolic rate (MR, unit: kcal/min) for prolonged periods allowing for activities of daily living 3 , and energy expenditure (EE, unit: kcal), which is the cumulative MR over time. Hence, MR and EE in the general sense are used interchangeably in the medical literature and in this paper. Human EE is comprised of various components and is influenced by many factors. The largest component of human EE is resting EE, which is the energy required to carry out fundamental physiological functions, contributing 60-80% of the total daily EE 4. RMR is influenced by various physiological characteristics, including gender 5 , ethnicity 6 , age 7, 8 , body composition 9,10 , various metabolic syndromes 11-16 , and gene variations 17. Additionally, resting MR (RMR) responds to environmental stimuli, such as cold temperatures 18,19 , food intake and dietary composition 20-24. Moreover, RMR drops significantly during sleep 25 and varies by circadian phase 26. A smaller, yet important component of human MR is activity-induced MR (AMR) 27. Activities can be subdivided into two categories: non-exercise activity thermogenesis (NEAT) and volitional exercise 28,29. NEAT includes occupational and leisure activities and any spontaneous activitie...
