Differences In Respiratory Exchange Ratio Research Articles

Sex Differences In Energy Expenditure, Metabolic Heat, And Substrate Utilization During Exercise-Heat Stress

Purpose: To understand the influence of repeated heat exposures and biological sex on metabolic outcomes surrounding heat acclimation (HA). Based on previous data, we hypothesized that repeated heat exposures would result in higher resting caloric expenditure and exercising metabolic heat production in men (vs. women). Methods: Twenty participants (65% men, 22±3 yrs, 70.1±13.7 kg, VO2max 49.9±6.8 mL·kg −1·min −1) had 8 daily exercise-heat sessions (40°C, 40%rh, at least 60min) including heat tolerance tests (HTT; 120 min, 3.1 mph, 2% grade) on days 1 and 8. Resting energy expenditure (REE) and respiratory exchange ratio (RER) were assessed pre- and post-HTT on days 1 and 8. Metabolic heat production (MHP) and RER were collected during the HTT. Data are presented as mean difference (MD) (95% confidence intervals). For REE and RER, a 2x2 ANOVA compared metrics before HTT vs. after HTT session, pre-HA vs. post HA with sex as a between-subjects factor. For MHP and RER during exercise, a dependent samples t-test compared pre-HA vs. post-HA and independent samples t-test compared sexes pre-HA vs. post-HA. Results: Pre-HA: RER was higher before vs. after the HTT (MD:0.07 (0.05,0.09) A.U., p<0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p>0.05) overall, but males had higher REE before HTT (MD:564 (291,836) kcal·day −1, p<0.001) and after HTT (MD:666 (395,938) kcal·day −1, p<0.001) than women. Post-HA: RER was higher before vs. after the HTT (MD:0.08 (0.06,0.10) A.U., p<0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p>0.05), but males had higher REE before (MD:581 (328,834) kcal·day −1, p<0.001) and after HTT (MD:617 (411,823) kcal·day −1, p<0.001) compared to women. Comparing HA Status: RER was not different between HA status before or after the HTT (p>0.05). REE was not different between HA status before the HTT (p>0.05). After HTT, REE was greater pre-HA compared to post-HA (MD:142 (26,259) kcal·day −1, p=0.019). During activity, MHP was greater pre-HA compared to post-HA (MD:14 (-2,31) W/m2, p=0.042); RER was not different (p>0.05). Pre-HA there were no differences in MHP or RER between sexes (p>0.05); post-HA, men had greater MHP than women (MD:36 (3,67) W/m2, p=0.016); there were no sex differences in RER. Conclusion: Men exhibited greater REE than women at each time point under both conditions and men produced more metabolic heat following HA. In response to completing 8 heat exposures as part of a HA protocol, men and women differed in caloric expenditure and MHP, but not in substrate utilization. Thus, our findings provide supporting evidence for sex-specific nutritional recommendations surrounding exercise-heat stress. Funding Source: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Intestinal FFA2 promotes obesity by altering food intake in Western diet-fed mice.

Short-chain fatty acids (SCFAs) are key nutrients that play a diverse set of roles in physiological function, including regulating metabolic homeostasis. Generated through the fermentation of dietary fibers in the distal colon by the gut microbiome, SCFAs and their effects are partially mediated by their cognate receptors, including free fatty acid receptor 2 (FFA2). FFA2 is highly expressed in the intestinal epithelial cells, where its putative functions are controversial, with numerous in vivo studies relying on global knockout mouse models to characterize intestine-specific roles of the receptor. Here, we used the Villin-Cre mouse line to generate a novel, intestine-specific knockout mouse model for FFA2 (Vil-FFA2) to investigate receptor function within the intestine. Because dietary changes are known to affect the composition of the gut microbiome, and can thereby alter SCFA production, we performed an obesogenic challenge on male Vil-FFA2 mice and their littermate controls (FFA2-floxed, FFA2fl/fl) to identify physiological changes on a high-fat, high-sugar 'Western diet' (WD) compared to a low-fat control diet (CD). We found that the WD-fed Vil-FFA2 mice were transiently protected from the obesogenic effects of the WD and had lower fat mass and improved glucose homeostasis compared to the WD-fed FFA2fl/fl control group during the first half of the study. Additionally, major differences in respiratory exchange ratio and energy expenditure were observed in the WD-fed Vil-FFA2 mice, and food intake was found to be significantly reduced at multiple points in the study. Taken together, this study uncovers a novel role of intestinal FFA2 in mediating the development of obesity.

Effect of gas exchange data selection methods on resting metabolic rate estimation in young athletes.

This cross-sectional study analysed the effect of the gas exchange data selection methods on the resting metabolic rate (RMR) estimation and proposed a protocol shortening providing a suitable RMR estimation for young athletes. Sixty-six healthy young Brazilian athletes performed a 30-minute RMR assessment. Different methods of gas exchange data selection were applied: short and long-time intervals, steady-state (SSt), and filtering. A mixed one-way ANOVA was used to analyse the mean differences in gas exchange, RMR, respiratory exchange ratio (RER), and coefficients of variation across all methods. Additionally, paired Student's t-test were used to compare the first and best SSt RMR values for each SSt method (3, 4, and 5-min). The 5-min SSt method provided the lowest RMR estimate (1454 kcal.day-1). There was a statistical difference between methods (F = 2.607, p = 0.04), but they presented a clinically irrelevant absolute difference (~36 kcal.day-1). There were no differences in RER among methods. In addition, using the SSt method, 12 minutes of assessment were enough to obtain a valid estimation of RMR. The 5-min SSt method should be employed for assessing the RMR among young athletes, considering the possibility of obtaining a shortened assessment (~12 min) with an acceptable and low coefficient of variation.

Effects of Grape Syrup Intake on Metabolic Rate and Substrate Oxidation During and After Sprint Intermittent Exercise

Background: Regarding sports drinks' role in substrate oxidation, the present study investigated the effect of grape syrup intake on metabolic rate and substrate oxidation after sprint intermittent exercise in active male students. Methods: In a double-blind, placebo-controlled, crossover study, 12 active male college students (body mass = 62.77 ± 9.05 kg; height = 173 ± 6.78 cm; BMI = 21 ± 2.5 kg/m2) were divided into two groups and performed two separate exercise sessions after grape syrup (1.1 mL/kg. body weight) or placebo intake. In the exercise session, subjects performed four 30-second Wingate tests (75 g / kg body weight) with a 5‐minute rest period. Energy expenditure (EE), respiratory exchange ratio (RER), fat oxidation (FO), heart rate (HR), and oxygen intake (VO2) were assessed 5 minutes before, during, and 30 minutes after exercise. Statistical analysis was performed using mixed-model ANOVA with repeated measures. Results: The results showed only between-group differences in respiratory exchange ratio (P = 0.04). However, the effect of time was significant between different situations (before, during, and after SIE) on all variables (P < 0.05). No time-group interaction effect was also observed in investigated variables (P > 0.05). The effect of different measurement times showed that in the post-SIE period, RER and fat oxidation rate values respectively decreased and increased compared to pre-SIE (P < 0.05) in both situations. Conclusions: The grape syrup intake improved metabolic rate and substrate oxidation during the recovery period after SIE, comparable to the placebo-containing synthetic carbohydrates. Therefore, it is recommended to use this herbal supplement as a substitute for a carbohydrate drink during SIE. However, more research is needed in this case.

The impact of natural menstrual cycle and oral contraceptive pill phase on substrate oxidation during rest and acute submaximal aerobic exercise.

Previous research has identified sex differences in substrate oxidation during submaximal aerobic exercise including a lower respiratory exchange ratio (RER) in females compared with males. These differences may be related to differences in sex hormones. Our purpose was to examine the impact of the natural menstrual cycle (NAT) and second- and third-generation oral contraceptive pill (OCP2 and OCP3) cycle phases on substrate oxidation during rest and submaximal aerobic exercise. Fifty female participants (18 NAT, 17 OCP2, and 15 OCP3) performed two experimental trials that coincided with the low (i.e., nonactive pill/early follicular) and the high hormone (i.e., active pill/midluteal) phase of their cycle. RER and carbohydrate and lipid oxidation rates were determined from gas exchange measurements performed during 10 min of supine rest, 5 min of seated rest, and two 8-min bouts of submaximal cycling exercise at ∼40% and ∼65% of peak oxygen uptake (V̇o2peak). For all groups, there were no differences in RER between the low and high hormone phases during supine rest (0.73 ± 0.05 vs. 0.74 ± 0.05), seated rest (0.72 ± 0.04 vs. 0.72 ± 0.04), exercise at 40% (0.77 ± 0.04 vs. 0.78 ± 0.04), and 65% V̇o2peak (0.85 ± 0.04 vs. 0.86 ± 0.03; P > 0.19 for all). Similarly, carbohydrate and lipid oxidation rates remained largely unchanged across phases during both rest and exercise, apart from higher carbohydrate oxidation in NAT vs. OCP2 at 40% V̇o2peak (P = 0.019) and 65% V̇o2peak (P = 0.001). NAT and OCPs do not appear to largely influence substrate oxidation at rest and during acute submaximal aerobic exercise.NEW & NOTEWORTHY This study was the first to examine the influence of NAT and two generations of OCPs on substrate oxidation during rest and acute submaximal aerobic exercise. We reported no differences across cycle phases or groups on RER, and minimal impact on carbohydrate or lipid oxidation apart from an increase in carbohydrate oxidation in NAT compared with OCP2 during exercise. Based on these findings, NAT/OCP phase controls may not be necessary in studies investigating substrate oxidation.

Progressive daily hopping exercise improves running economy in amateur runners: a randomized and controlled trial

This study investigated the effects of a daily plyometric hopping intervention on running economy (RE) in amateur runners. In a randomized, controlled trial, thirty-four amateur runners (29 ± 7 years, 27 males) were allocated to a control or a hopping exercise group. During the six-week study, the exercise group performed 5 min of double-legged hopping exercise daily. To progressively increase loading, the number of hopping bouts (10 s each) was steadily increased while break duration between sets was decreased. Pre- and post-intervention, RE, peak oxygen uptake (VO2peak), and respiratory exchange ratio (RER) were measured during 4-min stages at three running speeds (10, 12, and 14 km/h). ANCOVAs with baseline values and potential cofounders as cofactors were performed to identify differences between groups. ANCOVA revealed an effect of hopping on RE at 12 km/h (df = 1; F = 4.35; p < 0.05; η2 = 0.072) and 14 km/h (df = 1; F = 6.72; p < 0.05; η2 = 0.098), but not at 10 km/h (p > 0.05). Exercise did not affect VO2peak (p > 0.05), but increased RER at 12 km/h (df = 1; F = 4.26; p < 0.05; η2 = 0.059) and 14 km/h (df = 1; F = 36.73; p < 0.001; η2 = 0.520). No difference in RER was observed at 10 km/h (p > 0.05). Daily hopping exercise is effective in improving RE at high running speeds in amateurs and thus can be considered a feasible complementary training program.Clinical trial registration German Register of Clinical Trials (DRKS00017373).

Abstract P3027: Intermittent Fasting Improves High Fat Diet Mediated Heart Failure With Preserved Ejection Fraction

Intermittent fasting (IF) has improved metabolic aberrations in metabolic diseases, however, the mechanism is unclear. Our lab focuses on 4-hydroxy-2-nonenal (4HNE), an oxidative stress byproduct which accumulates in metabolic diseases, in cardiac damage and activity of aldehyde dehydrogenase 2 (ALDH2), a 4HNE detoxifying enzyme, which was implicated in cardioprotection. We reported that the ALDH2*2 knock-in mutant mice (AL) with low intrinsic ALDH2 activity that were fed with high-fat diet (HFD) exhibited severe heart failure with preserved ejection fraction (HFpEF) compared to HFD fed control mice (C57). We hypothesized that IF can contribute to the improvement of HFpEF even in AL mice by reducing 4HNE. C57 and AL mice that were fed HFD and L-NAME (nitric oxide inhibitor) in drinking water were grouped as C57-free and AL-free meaning taking food freely or C57-IF and AL-IF meaning daily 16 hours fasting with 8-hr free access to food. After 2-months of HFD feeding, the body weights of C57-IF (35.5±3.8g) and AL-IF (36.7±3.4g) groups were significantly lower than C57-free (43.5±4.2g, p&lt;0.05 vs C57-IF) and AL-free (45.8±5.6g, p&lt;0.05 vs AL-IF) groups. The 24-hour food intakes of C57-IF (8.6±0.9 KCal) and AL-IF (8.8±1.1 KCal) were significantly decreased, compared to C57-free (12.3±1.7 KCal, p&lt;0.05 vs C57-IF) and AL-free (13.3±1.5 KCal, p&lt;0.05 vs AL-IF) groups. The respiratory exchange ratio (RER) of AL-free group (0.62±0.12) was significantly lower than three other groups (p&lt;0.05 vs C57-free, C57-IF and AL-IF, respectively). The E/A ratio (E/A), a diastolic parameter, was decreased in C57-free (1.14±0.21) and AL-free (0.89±0.17) groups, not in C57-IF (2.15±0.31, p&lt;0.05 vs C57-free) and AL-IF (1.97±0.25, p&lt;0.05 vs AL-free) groups. The E/A in AL-free group was also lower than C57-free group (p&lt;0.05). Another diastolic parameter, isovolumic relaxation time (IVRT) was also prolonged in C57-free (27.3±3.3 ms) and AL-free (29.4±3.7 ms) mice, not in C57-IF (13.3±1.8 ms, p&lt;0.05 vs C57-free) and AL-IF (15.2±2.1 ms, p&lt;0.5 vs AL-free) mice. In conclusion, IF decreased food intake and obesity, and improved metabolism and heart function in both C57 and ALDH2*2 mice with HFpEF, and also diminished the differences in RER and E/A between them via lowering the 4HNE adducts.

Individuals With Type 1 Diabetes May Have Altered Metabolic Responses During Exercise

Individuals with type 1 diabetes (T1D) benefit from regular physical activity (PA). Despite the positive gains, more than 60% of people with T1D do not meet current PA recommendations. Previous research suggests exercise has mixed effects on blood glucose (BG). Understanding the influence of exercise intensity substrate metabolism in individuals with T1D during various intensities of exercise is essential in providing appropriate recommendations for PA in those with T1D. PURPOSE: The purpose of this study is to examine energy metabolism during a graded exercise test, specifically fuel substrate usage as assessed respiratory exchange ratio (RER) and blood metabolites in individuals with T1D in comparison to individuals without T1D. METHODS: Individuals with T1D were matched for sex and PA level with healthy individuals without T1D (N = 14; 7 per group). Each individual participated in a GXT on an electronically braked cycle ergometer. BG, blood lactate, and RPE were measured every two minutes. Gas exchange, including RER, were measured throughout the GXT using the ParvoMedics system. VO2peak was judged as >90% age predicted maximal heart rate and RPE >16 on the Borg scale. Mixed model regression was used to estimate the trajectory of change in all outcomes during GXT. RESULTS: Demographics and VO2peak were not statistically significant between groups (p > 0.05). There were no significant differences in RER at peak workload between T1D (1.06 +/-0.049) and controls (1.05+/-0.031) t(12) = 0.456, p = 0.66. There were no significant differences in blood lactate at peak workload between T1D (10.37+/-3.07) and controls (8.514+/-3.11) t(12) = 1.1237, p = 0.28. The estimated trajectory of change in RER (B = 0.014, p < 0.001), lactate (B = 0.379, p = 0.004), glucose (B = 1.521, p = 0.060), and RPE (B = 0.202, p = 0.018) were significantly higher in individuals with T1D during GXT as compared to controls. CONCLUSIONS: Our results suggest that individuals with T1D may have altered metabolic responses during exercise, shifting to anaerobic exercise and carbohydrate utilization at lower intensities. This could be due to altered carbohydrate or lipid metabolism. Additional research with larger sample sizes is needed to examine the effects of exercise interventions on metabolism and various fitness goals as well as glucose management.

Impact of Immune Function on Aerobic Capacity in Rats

BackgroundThe use of immunocompromised animals has been indispensable in cancer and immunology research. The use of exercise with these models in these areas of research has increased dramatically over the past decade, with little to no evidence of how immune modification of strains of animals is impacting exercise capacity and/or responses to training. This data is critical for extrapolation to exercise recommendations in humans as the majority of cancer patients do not present with primary immunodeficiency diseases. Recently, observations of lower skeletal muscle oxidative capacity between RNU (NIH Nude, immunocompromised) and Copenhagen rats (immunocompetent) have been speculated to result from possible differences between immune function in animals. The purpose of this study was to determine if there are differences in maximal aerobic capacity, through assessment of V̇o2max, between immune‐competent and ‐compromised animals of the same strain. We tested the hypothesis that immunocompromised animals would have a lower aerobic capacity than their immunocompetent counterparts.MethodsRNU 316 (NU−/−, T‐cell deficient; n=10) and RNU 118 (NU+/−, no deficiency; n=10) male rats (~4 months old) were obtained from Charles River. Both groups were acclimated to motorized treadmill running at varying speeds (20–40 m/min) for 3–5 sessions before beginning V̇o2max assessment. V̇o2max graded treadmill testing consisted of a 2‐minute warm‐up at 25 m/min at a 5% incline followed by 2 minutes at 35 m/min, and subsequent increases in speed of 5 m/min every minute after until a plateau was seen in oxygen consumption with increased speed, or test termination was required for safety of the animal. Tests were repeated a minimum of two times (3 maximally) per animal to verify maximum values were achieved.ResultsThere were no significant differences in body mass (NU−, 347±12 g, NU+, 321±8 g; p=0.17). V̇o2max was lower in NU− vs NU+ animals (80.0±1.5 vs. 88.4±1.9 ml·min−1·kg−1; p&lt;0.01). There was a significant difference in respiratory exchange ratio (RER) at V̇o2max (NU−, 1.05±0.01 vs. NU+, 0.98±0.01; p&lt;0.05), but no difference in CO2 production (NU−, 83.7±1.3 vs. NU+, 86.7±1.5 ml·min−1·kg−1; p&gt;0.05).ConclusionThis study suggests that immunocompromised animals have a decreased aerobic capacity compared to immunocompetent counterparts. This should be considered when both designing exercise interventions in immunedeficient/compromised animals as well as interpretations derived from such studies.Support or Funding InformationNIH HL137156‐01A1ACS RSG‐14‐150‐01‐CCE

Eating breakfast and avoiding late-evening snacking sustains lipid oxidation.

Circadian (daily) regulation of metabolic pathways implies that food may be metabolized differentially over the daily cycle. To test that hypothesis, we monitored the metabolism of older subjects in a whole-room respiratory chamber over two separate 56-h sessions in a random crossover design. In one session, one of the 3 daily meals was presented as breakfast, whereas in the other session, a nutritionally equivalent meal was presented as a late-evening snack. The duration of the overnight fast was the same for both sessions. Whereas the two sessions did not differ in overall energy expenditure, the respiratory exchange ratio (RER) was different during sleep between the two sessions. Unexpectedly, this difference in RER due to daily meal timing was not due to daily differences in physical activity, sleep disruption, or core body temperature (CBT). Rather, we found that the daily timing of nutrient availability coupled with daily/circadian control of metabolism drives a switch in substrate preference such that the late-evening Snack Session resulted in significantly lower lipid oxidation (LO) compared to the Breakfast Session. Therefore, the timing of meals during the day/night cycle affects how ingested food is oxidized or stored in humans, with important implications for optimal eating habits.

The RNA binding protein HuR influences skeletal muscle metabolic flexibility in rodents and humans

BackgroundMetabolic flexibility can be assessed by changes in respiratory exchange ratio (RER) following feeding. Though metabolic flexibility (difference in RER between fasted and fed state) is often impaired in individuals with obesity or type 2 diabetes, the cellular processes contributing to this impairment are unclear. Materials and methodsFrom several clinical studies we identified the 16 most and 14 least metabolically flexible male and female subjects out of >100 participants based on differences between 24-hour and sleep RER measured in a whole-room indirect calorimeter. Global skeletal muscle gene expression profiles revealed that, in metabolically flexible subjects, transcripts regulated by the RNA binding protein, HuR, are enriched. We generated and characterized mice with a skeletal muscle-specific knockout of the HuR encoding gene, Elavl1 (HuRm−/−). ResultsMale, but not female, HuRm−/− mice exhibit metabolic inflexibility, with mild obesity, impaired glucose tolerance, impaired fat oxidation and decreased in vitro palmitate oxidation compared to HuRfl/fl littermates. Expression levels of genes involved in mitochondrial fatty acid oxidation and oxidative phosphorylation are decreased in both mouse and human muscle when HuR is inhibited. ConclusionsHuR inhibition results in impaired metabolic flexibility and decreased lipid oxidation, suggesting a role for HuR as an important regulator of skeletal muscle metabolism.

Sexual dimorphism of substrate utilization: Differences in skeletal muscle mitochondrial volume density and function.

What is the central question of this study? Females rely to a greater extent than males on fat oxidation during exercise. Whether any difference in skeletal muscle mitochondrial phenotype and oxidative capacity contributes to this sexual dimorphism remains incompletely explored. What is the main finding and its importance? Female prioritization of fat during exercise occurs in parallel to augmented mitochondrial volume density and intrinsic fatty acid and lactate oxidation in skeletal muscle fibres compared with males, independently of aerobic exercise capacity. The enlarged metabolic machinery in skeletal muscle of females is associated with lower body size and leg mass. Fat oxidation during exercise is greater in females than in males. We sought to determine whether sex differences in substrate metabolism are paralleled by distinct skeletal muscle mitochondrial volume density and oxidative capacity. Whole-body substrate (fat and carbohydrate) utilization during submaximal treadmill running was assessed, and skeletal muscle biopsies were taken to determine mitochondrial volume density and function in healthy young females (n=12) and males (n=12) matched by aerobic exercise capacity and exercise performance. Females presented a lower respiratory exchange ratio (0.87±0.04 versus 0.91±0.04, P=0.023) and whole-body carbohydrate oxidation (27.8±8.3 versus 35.8±6.5mgkg-1 min-1 , P=0.027), whereas fat oxidation was higher (8.7±2.8 versus 5.9±2.6mgkg-1 min-1 , P=0.034) during submaximal exercise compared with males. In skeletal muscle biopsies, females demonstrated augmented mitochondrial volume density (7.51±1.77 versus 5.90±1.72%, P=0.035) and oxidative capacity for fatty acid [36.6±12.8 versus 24.5±7.3pmol O2 s-1 (mg wet weight)-1 , P=0.009] and lactate [71.1±24.4 versus 53.2±14.6pmol O2 s-1 (mg wet weight)-1 , P=0.040]. No sex differences in respiratory exchange ratio, whole-body fat oxidation and skeletal muscle variables were detected when adjusted for anthropometric variables including body mass or leg mass, which were lower in females. In conclusion, female prioritization of fat over carbohydrate oxidation during exercise is underpinned by augmented body size-related mitochondrial volume density, fatty acid and lactate oxidative capacity in skeletal muscle fibres.

SORCS1 and SORCS3 control energy balance and orexigenic peptide production.

SORCS1 and SORCS3 are two related sorting receptors expressed in neurons of the arcuate nucleus of the hypothalamus. Using mouse models with individual or dual receptor deficiencies, we document a previously unknown function of these receptors in central control of metabolism. Specifically, SORCS1 and SORCS3 act as intracellular trafficking receptors for tropomyosin‐related kinase B to attenuate signaling by brain‐derived neurotrophic factor, a potent regulator of energy homeostasis. Loss of the joint action of SORCS1 and SORCS3 in mutant mice results in excessive production of the orexigenic neuropeptide agouti‐related peptide and in a state of chronic energy excess characterized by enhanced food intake, decreased locomotor activity, diminished usage of lipids as metabolic fuel, and increased adiposity, albeit at overall reduced body weight. Our findings highlight a novel concept in regulation of the melanocortin system and the role played by trafficking receptors SORCS1 and SORCS3 in this process.

Substrate oxidation in female adults during endurance exercise throughout menstrual cycle phases: IronFEMME pilot study

The main aim of the study was to investigate the effect of menstrual cycle phases on substrate oxidation during steady state intensity exercise in adult females with regular menstrual cycle and on oral contraceptive (OC). Twenty-four healthy endurance and strength trained females, with regular menstrual cycle phases (n= 15; Age 35.6±4.2; height 163.9±5.9 cm; body mass 58.1±5.2 kg; VO2peak 50.3±3.6 ml·min-1·kg-1) or on oral contraceptives (n=9; Age 30.4±4.5; height 163.9±9.0 cm; body mass 58.1±6.7 kg; VO2peak 52.4±4.2 ml·min-1·kg-1) participated in the study. All participants performed a graded maximal exercise test to determine their peak oxygen consumption (VO2peak). Participants then exercised at the speed corresponding to 75% of VO2peak for 40 minutes on a treadmill in each menstrual cycle phase: regular menstrual cycle group (early follicular phase, mid-follicular phase and luteal phase) and OC group (hormonal phase and non-hormonal phase). There were no differences in the respiratory exchange ratio of each phase, in regular menstrual cycle phase group (mean±SEM): early-follicular phase 0.89±0.01, mid-follicular phase 0.87±0.01 and luteal phase 0.88±0.01 (p>0.05). There were also no differences in respiratory exchange ratio for the participants using oral contraceptive: hormonal phase 0.89±0.01 and non-hormonal phase 0.91±0.01 (p>0.05). However, we found that OC may influence fat oxidation (p=0.018) during the hormonal phase. Our preliminary results suggest that menstrual cycle and oral contraceptive do not influence substrate oxidation in females with regular menstrual cycle phases. Regarding the few disparities, more research is needed to understand how sexual hormones influence substrate oxidation in female.

Metabolic characterization of overweight and obese adults

ABSTRACTObjectives: Traditional evaluations of metabolic health may overlook underlying dysfunction in individuals who show no signs of insulin resistance or dyslipidemia. The purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional cardiometabolic variables. A secondary purpose was to evaluate differences between overweight/obese and male/female cohorts, respectively.Methods: Forty-nine overweight and obese adults (Mean ± SD; Age = 35.0 ± 8.9 yrs; Body mass index = 33.6 ± 5.2 kg·m−2; Percent body fat [%fat] = 36.7 ± 7.9%) were characterized. Body composition (fat mass [FM], lean mass [LM], %fat) was calculated using a 4-compartment model; visceral adipose tissue (VAT) was quantified using B-mode ultrasound. Resting metabolic rate (RMR) and respiratory exchange ratio (RER) were evaluated using indirect calorimetry. Fasted blood and saliva samples were analyzed for total cholesterol (TC), high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglycerides (TRG), glucose (GLUC), insulin, leptin, estradiol, and cortisol.Results: The prevalence of individuals with two or more cardiometabolic risk factors increased from 13%, using traditional risk factors (GLUC, TRG, HDL), to 80% when non-traditional metabolic factors (VAT, LM, RMR, RER, TC, LDL, HOMA-IR) were considered. Between overweight/obese, there were no significant differences in %fat (p = 0.152), VAT (p = 0.959), RER (p = 0.493), lipids/GLUC (p > 0.05), insulin (p = 0.143), leptin (p = 0.053), or cortisol (p = 0.063); obese had higher FM, LM, RMR, and estradiol (p < 0.01). Males had greater LM, RMR, and TRG (p < 0.01); females had greater %fat, and leptin (p < 0.001). There were no significant sex differences in RER, estradiol, insulin, or cortisol (p > 0.05).Conclusions: Evaluating metabolic health beyond BMI and traditional cardiometabolic risk factors can give significant insights into metabolic status. Due to high variability in metabolic health in overweight and obese adults and inherent sex differences, implementation of body composition and visceral fat measures in the clinical setting can improve early identification and approaches to disease prevention.

Time-restricted feeding reduces adiposity in mice fed a high-fat diet

Disruption of the circadian rhythm contributes to obesity. This study tested the hypothesis that time-restricted feeding (TRF) reduces high-fat diet–induced increase in adiposity. Male C57BL/6 mice were fed the AIN93G or the high-fat diet ad libitum (ad lib); TRF of the high-fat diet for 12 or 8hours during the dark cycle was initiated when high-fat diet–fed mice exhibited significant increases in body weight. Energy intake of the TRF 12-hour group was not different from that of the high-fat ad lib group, although that of the TRF 8-hour group was slightly but significantly lower. Restricted feeding of the high-fat diet reduced body fat mass and body weight compared with mice fed the high-fat diet ad lib. There were no differences in respiratory exchange ratio (RER) among TRF and high-fat ad lib groups, but the RER of these groups was lower than that of the AIN93G group. Energy expenditure of the TRF groups was slightly but significantly lower than that of the high-fat ad lib group. Plasma concentrations of ghrelin were increased in TRF groups compared with both AIN93G and high-fat ad lib groups. Elevations of plasma concentrations of insulin, leptin, monocyte chemoattractant protein-1, and tissue inhibitor metalloproteinase-1 by high-fat ad lib feeding were reduced by TRF to the levels of mice fed the AIN93G diet. In conclusion, TRF during the dark cycle reduces high-fat diet–induced increases in adiposity and proinflammatory cytokines. These results indicate that circadian timing of food intake may prevent obesity and abate obesity-related metabolic disturbance.

COMPARAISON OF HEART RATE RECOVERY AND PARASYMPATHETIC REACTIVATION PARAMETERS AFTER A MAXIMAL EXERCICE, A MODERATE-INTENSITY CONTINUOUS EXERCISE AND HIGH-INTENSITY INTERVAL EXERCISE IN YOUNG AND OLD HEALTY SUBJECTS AND STABLE CORONARY PATIENTS

controlled trial of 39 low-risk patients 4 weeks to 6 months post ACS, EF > 40%, fully revascularized, were randomized to 12 to 18 weeks of 2-3 sessions/week (36 sessions total) of isocaloric MICET or HIIT on cycle ergometer. MICET protocol: 5 min warm-up at 30% maximal aerobic power (MAP) followed by 37 min at 60% MAP, followed by 5 min warm down at 30% MAP. HIIT included 3 sets of 10 minutes of repeated phases of 15 sec at 100 MAP alternating with 15 sec passive recovery. Warm up and cool down: 5 min at 30% MAP. MAP was determined using graded maximal cardiopulmonary exercise test (CPET) on cycle ergometer and continuous ECG and BP monitoring every 2 min. Metabolic and anthropometric profile, holter monitoring, as well as CPET was repeated before and after the intervention. RESULTS: 1 patient has yet to complete the intervention; complete data available for 35 patients (16 HIIT, 16 MICET). Baseline data is presented in Table 1. Significant improvement in VO2max was observed in both groups, with a greater increase seen in patients utilizing MICET (difference 102.4 46 vs 309.9 54 ml, p 1⁄4 0.011; 1.8 0.89 vs 3.5 0.84 ml/kg lean body mass difference, p1⁄40.018). No difference in respiratory exchange ratio at peak effort was observed (1.18 vs 1.16). No significant differences in systolic BP, weight, HRR, fasting lipids, glucose or insulin sensitivity were observed. No adverse events or ventricular arrhythmias were noted to be associated with exercise training. CONCLUSION: Both training modalities result in improvements in VO2max with greater effect in those using MICET. HIIT appears to be well tolerated in patients post ACS.

Metabolic, Cardiovascular, and Perceptual Responses to a Thermogenic Nutritional Supplement at Rest, During Exercise, and Recovery in Men

Twenty-one men (mean ± SD; age = 23.5 ± 2.6 years, BMI = 26.0 ± 2.4 kg-1·m-2) completed this randomized, double-blinded, placebo-controlled, crossover study to examine acute responses to a thermogenic nutritional supplement. Each testing session included: (a) 30 minutes resting, followed by placebo or thermogenic nutritional supplementation, (b) 50 minutes postsupplementation resting, (c) 60 minutes walking, and (d) 50 minutes postexercise recovery. Gas exchange variables and heart rate (HR) were recorded during each phase. Blood pressure was recorded during all phases except exercise. Ratings of perceived exertion (RPE) were recorded only during exercise. There were no significant differences for any of the measures between the supplement and placebo during the initial resting or postsupplementation phases. During exercise, energy expenditure (EE) (placebo = 18.98-19.06 kJ·min-1 and supplement = 19.44-19.82 kJ·min-1) and VO2 (placebo = 11.27-11.35 ml·kg-1·min-1; supplement = 11.64-11.82 ml·kg-1·min-1) were greater for the supplement than placebo. There were no differences in respiratory exchange ratio (RER), HR, or RPE between the supplement and placebo during exercise. Postexercise, only VO2 (placebo = 3.53-3.63 ml·kg-1·min-1; supplement = 3.71-3.84 ml·kg-1·min-1) was greater for the supplement than placebo, but there were no differences in EE, RER, HR, or blood pressure. These findings suggested that the specific blend of ingredients in the thermogenic nutritional supplement, when combined with exercise, increased the metabolic rate with minimal changes in cardiovascular function and no effect on RPE.

Fasting substrate oxidation in relation to habitual dietary fat intake and insulin resistance in non-diabetic women: a case for metabolic flexibility?

BackgroundMetabolic flexibility described as “the capacity of the body to match fuel oxidation to fuel availability” has been implicated in insulin resistance. We examined fasting substrate oxidation in relation to dietary macronutrient intake, and markers of insulin resistance in otherwise healthy women, with and without a family history of diabetes mellitus (FH DM).MethodsWe measured body composition (dual x-ray absorptiometry), visceral and subcutaneous adipose tissue area (VAT, SAT, using Computerised Tomography), fasting [glucose], [insulin], [free fatty acids], [blood lipids], insulin resistance (HOMA-IR), resting energy expenditure (REE), respiratory exchange ratio(RER) and self-reported physical activity in a convenience sample of 180 women (18-45 yrs). A food frequency questionnaire was used to assess energy intake (EI) and calculate the RER: Food Quotient (FQ) ratio. Only those with EI:REE (1.05 -2.28) were included (N=140). Insulin resistance was defined HOMA-IR (>1.95).ResultsThe Insulin Resistant (IR) group had higher energy, carbohydrate and protein intakes (p < 0.05) and lower PA levels than Insulin Sensitive (IS) group (P < 0.001), but there were no differences in RER or RER:FQ between groups. However, nearly 50% of the variance in HOMA-IR was explained by age, body fat %, VAT, RER:FQ and FH DM (adjusted R2 = 0.50, p < 0.0001). Insulin-resistant women, and those with FH DM had a higher RER:FQ than their counterparts (p < 0.01), independent of body fat % or distribution.ConclusionIn these apparently healthy, weight-stable women, insulin resistance and FH DM were associated with lower fat oxidation in relation to dietary fat intake, suggesting lower metabolic flexibility.

Cycling exercise to resist electrically stimulated antagonist increases oxygen uptake in males: Pilot study

A hybrid training system (HTS) has been developed as the combined application of electrical stimulation (ES) and volitional contractions (VC), using electrically stimulated eccentric antagonist muscle contractions as a resistance to voluntary agonist muscle contractions. The purpose of the present study is to compare the metabolic cost between cycling exercise using HTS as added resistance (HTC) and unloaded cycling exercise (ULC). Twelve male subjects exercised on a leg cycle ergometer. After 5 min rest and 5 min warm up, they performed ULC for 5 min or HTC for 5 min. During rest and each exercise, the steady state of oxygen uptake (VO2), carbon dioxide output (VCO2), expired ventilation (VE), respiratory exchange ratio (RER), and heart rate (HR) were measured. The values of VO2, VCO2, VE, and HR during HTC were significantly greater than during ULC (p < 0.05). Relative VO2 was 16.7% +/- 2.1% of peak VO2 during ULC, and it was 21.1% +/- 3.4% during HTC. However, there was no significant difference in RER between ULC and HTC. These findings indicate that the combined application of VC and ES could lead to a greater increase in metabolic cost. HTS seems to be applicable as a resistance of motion.