In humans, the variation in resting metabolic rate (RMR) might be associated with health-related factors, as suggested by previous studies. This study explored whether the intra-assessment RMR variability (expressed as a coefficient of variation (CV; %)) is similar in men and women and if it is similarly associated with diverse health-related factors. The RMR of 107 young, and relatively healthy adults, was assessed using indirect calorimetry. Then, the CV for volumes of oxygen consumption (VO2) and carbon dioxide production (VCO2), respiratory exchange ratio (RER), and resting energy expenditure (REE) were computed as indicators of intra-assessment RMR variability. Body composition, cardiorespiratory fitness (peak VO2 uptake), circulating cardiometabolic risk factors, and heart rate and its variability (HR and HRV) were assessed. Men presented higher CVs for VO2, VCO2, and REE (all p <= 0.001) compared to women. Furthermore, in men, the intra-assessment RER variability was associated with vagal-related HRV parameters and with mean HR (standardized beta = -0.36, -0.38, and 0.41, respectively; all p < 0.04). In contrast, no associations were observed in women. In conclusion, men exhibited higher variability (CVs for VO2, VCO2, and REE) compared to women. The CV for RER could be a potential marker of cardiometabolic risk in young men., This research was funded by the Spanish Ministry of Economy and Competitiveness
(DEP2016-79512-R and PTA 12264-I). J.M.A.A., F.J.O.P., and A.P.F. are supported by the Spanish Ministry of Education, Culture and Sport (FPU15/04059, FPU16/02828, and FPU 16/02760, respectively). J.M.A.A. is supported by the University of Granada, Plan Propio de Investigación 2020 Programa de Contratos Puente, and by the Grant FJC2020-044453-I funded by MCIN/AEI/10.13039/501100011033
and by “European Union NextGenerationEU/PRTR”. F.J.O.P. is supported by the University of
Granada, Plan Propio de Investigación 2022 Programa de Contratos Puente. A.P.F. is supported in part by NIH grant #: U01 TR002004 (REACH project). Additional support was obtained from the
Unit of Excellence on Exercise and Health (UCEES) and the EXERNET Research Network on Exercise
and Health in Special Populations (DEP2005-00046/ACTI). This study was additionally supported by the Unit of Excellence in Sport and Health (UCEES), granted by the University of Granada and Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades and European Regional Development Funds (ref. SOMM17/6107/UGR).

Background: Numerous physiological responses to exercise are observed in humans, yet the effects of long-term exercise and varying intensities on the diversity and composition of human fecal microbiota remain unclear. We investigated the effect of a 24-week supervised concurrent exercise intervention, at moderate and vigorous intensities, on fecal microbiota diversity and composition in young adults.
Methods: This ancillary study was based on data from the ACTIBATE randomized controlled trial (ClinicalTrials.gov ID: NCT02365129), and included adults (aged 18–25 years, 70 % female) that were randomized to (i) a control group (CON: no exercise, n = 20), (ii) a moderate-intensity exercise group (MOD-EX, n = 21), and (iii) a vigorous-intensity exercise group (VIG-EX, n = 20). Fecal samples were collected before and after the 24-week exercise intervention, and the diversity and composition of the fecal microbiota were analyzed by 16S rRNA sequencing. Inferential functional profiling of the fecal microbiota was performed and correlations between microbial changes and cardiometabolic outcomes were assessed.
Results: Exercise did not modify beta or alpha diversities regardless of the intensity (all P ≥ 0.062). The relative abundance of the Erysipelotrichaceae family (Bacillota phylum) (−0.3 ± 1.2 %; P = 0.031) was however reduced in the VIG-EX group. Coprococcus was the only genus showed a significant difference between MOD-EX and VIG-EX after the intervention, with its relative abundance increasing in MOD-EX (+0.4 ± 0.6 %; P = 0.005). None of these changes were related to the exercise-induced cardiometabolic benefits (all P ≥ 0.05).
Conclusions: In young adults, a 24-week supervised concurrent exercise program, at moderate and vigorous intensities, resulted in minor changes in fecal microbiota composition, while neither alpha nor beta diversities were affected.
Clinical trial registration: ClinicalTrials.gov ID: NCT02365129., The study was supported by the Spanish Ministry of Economy and Competitiveness via Fondo de Investigación Sanitaria del Instituto de Salud Carlos III (PI13/01393) and PTA 12264-I, Retos de la Sociedad (DEP2016- 79512-R), and European Regional Development Funds (ERDF), by the Spanish Ministry of Education (FPU13/04365, FPU15/04059, FPU16/05159, FPU16/02828, FPU17/01523 and FPU19/01609), the Fundación Iberoamericana de Nutrición (FINUT), the University of Granada Plan Propio de Investigación 2016-Excellence actions: Unit of Excellence on Exercise and Health (UCEES), AstraZeneca HealthCare Foundationand by the Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades (ERDF, SOMM17/6107/UGR), the Junta de Andalucía, Consejería de Economía, Conocimiento, Empresas y Universidad (ref. P18-RT-4455); InFLAMES Flagship Programme of the Academy of Finland (decision number: 337530), Grant FJC2020-044453-I funded by MCIN/AEI/10.13039/501100011033 and by “European Union NextGenerationEU/PRTR”. BMT was funded (Grant RYC2022-036473-I) by MCIN/AEI/10.13039/501100011033 and by ESF+. This project was partially funded by EASO-New Clinical Investigator Award 2024 and by the EFSD-Rising Star 2024.

Exercise modulates both brown adipose tissue (BAT) metabolism and white
adipose tissue (WAT) browning in murine models. Whether this is true in
humans, however, has remained unknown. An unblinded randomized controlled trial (ClinicalTrials.gov ID: NCT02365129) was therefore conducted to
study the effects of a 24-week supervised exercise intervention, combining
endurance and resistance training, on BAT volume and activity (primary outcome). The study was carried out in the Sport and Health University Research
Institute and the Virgen de las Nieves University Hospital of the University of
Granada (Spain). One hundred and forty-five young sedentary adults were
assigned to either (i) a control group (no exercise, n = 54), (ii) a moderate
intensity exercise group (MOD-EX, n = 48), or (iii) a vigorous intensity exercise
group (VIG-EX n = 43) by unrestricted randomization. No relevant adverse
events were recorded. 97 participants (34 men, 63 women) were included in
the final analysis (Control; n = 35, MOD-EX; n = 31, and VIG-EX; n = 31). We
observed no changes in BAT volume (Δ Control: −22.2 ± 52.6 ml; Δ MOD-EX:
−15.5 ± 62.1 ml, Δ VIG-EX: −6.8 ± 66.4 ml; P = 0.771) or 18F-fluorodeoxyglucose
uptake (SUVpeak Δ Control: −2.6 ± 3.1 ml; Δ MOD-EX: −1.2 ± 4.8, Δ VIG-EX:
−2.2 ± 5.1; p = 0.476) in either the control or the exercise groups. Thus, we did
not find any evidence of an exercise-induced change on BAT volume or activity
in young sedentary adults., This study was funded by the Spanish Ministry of Economy and Competitiveness via the Fondo de Investigación Sanitaria del Instituto de Salud Carlos III (PI13/01393; J.R.R.) and PTA-12264I, Retos de la Sociedad (DEP2016-79512-R; J.R.R.) and European Regional Development Funds (ERDF; J.R.R.), the Spanish Ministry of Education (FPU13/04365 (G.S.D.), FPU14/04172 (F.A.G.), FPU15/04059 (J.M.A.), FPU16/03653 (A.M.G.), FPU16/02828 (F.J.O.P.), FPU16/05159 (H.X.), FPU17/01523 (L.O.A.), FPU19/01609 (L.J.F.)), International Doctoral Studies Scholarship no. 440575 from the Mexican National Council of Science and Technology (CONACYT; WDMA), the Fundación Iberoamericana de Nutrición (FINUT; JRR), the Redes Temáticas de Investigación Cooperativa RETIC (Red SAMID RD16/0022; J.R.R.), the AstraZeneca HealthCare Foundation (J.R.R.), the University of Granada Plan Propio de Investigación 2016 -Excellence actions: Unit of Excellence on Exercise and Health (UCEES) (J.R.R.)- and Plan Propio de Investigación 2018 - Programa Contratos-Puente and Programa Perfecionamiento de Doctores (G.S.D.), the Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades (ERDF; ref. SOMM17/6107/UGR; JRR), the Junta de Andalucía, Consejería de Economía, Conocimiento, Empresas y Universidad (ref. P18-RT-4455; J.R.R.), the Fundación Alfonso Martín Escudero (B.M.T. and G.S.D.), the Maria Zambrano fellowship by the Ministerio de Universidades y la Unión Europea NextGenerationEU (RR_C_2021_04; B.M.T.), and the Novo Nordisk Foundation (NNF18OC0032394; M.S.).