Understanding the factors that effect maximal fat oxidation

Is lean mass quantity or quality the determinant of maximal fat oxidation capacity? The potential mediating role of cardiorespiratory fitness

BACKGROUND

Impaired fat oxidation is linked to cardiometabolic risk. Maximal fat oxidation rate (MFO) reflects metabolic flexibility and is influenced by lean mass, muscle strength, muscle quality - defined as the ratio of strength to mass - and cardiorespiratory fitness. The relationship between these factors and fat oxidation is not fully understood. The aim is to analyze the associations of lean-mass, muscle strength and quality with fat oxidation parameters in young adults, considering the mediating role of VO2max.

METHODS

A cross-sectional observational study. Eighty-one adults (50 males, 31 females; age 22.8 ± 4.4, BMI 25.70 ± 5.75, lean-mass 54.19 ± 8.78, fat-mass 18.66 ± 11.32) Body composition assessment by bioimpedance determine fat and lean-mass. Indirect calorimetry at rest and exercise was used for the calculation of fat oxidation. An incremental exercise protocol in a cycle ergometer with two consecutive phases was performed. The first to determine MFO consisted of 3 min steps of 15W increments with a cadence of 60rpm. The test was stopped when RQ ≥ 1. After 5 min rest, a phase to detect VO2max began with steps of 15W/min until exhaustion. Muscular strength was assessed by handgrip dynamometry and the standing longitudinal jump test. A strength cluster was calculated with handgrip and long jump adjusted by sex and age. Data were analyzed using multiple linear regression and mediation analyses.

RESULTS

Total lean-mass and leg lean-mass were not associated with MFO. Long jump, relativized by lean-mass and by leg lean-mass have a standardized indirect effect on MFO of 0.50, CI: 0.32-0.70, on MFO/lean-mass 0.43, CI:0.27-0.60 and MFO/leg lean-mass 0.44, CI: 0.30-0.06, which VO2max mediated, VO2max/lean-mass and VO2max/leg lean-mass, respectively (all p < 0.01). The handgrip/arm lean-mass had an indirect effect of 0.25 (CI: 0.12-0.38) on MFO/leg lean-mass, with VO2max/leg lean-mass as the mediator (p < 0.01). The Cluster/lean-mass and Cluster/Extremities lean-mass have a standardized indirect effect on MFO/lean-mass (0.34, CI: 0.20-0.48) and MFO/leg lean-mass (0.44, CI: 0.28-0.60), mediated by VO2max/lean-mass and VO2max/leg lean-mass (p < 0.01).

CONCLUSIONS

Muscular strength and quality have an indirect effect on MFO mediated by VO2max. These findings suggest the importance of muscle quality on MFO.

Dynamic Response of Musclin, a Myokine, to Aerobic Exercise and Its Interplay With Natriuretic Peptides and Receptor C

OBJECTIVES

Musclin, recently identified as a myokine, has been recognized for its physiological significance in potentiating the functional properties of natrieutic peptides (NPs) through competitive inhibition of their clearance receptor, natrieutic peptide receptor C (NPR-C). This study, for the first time in the literature, investigated the dynamic response of musclin during and after aerobic exercise in humans, exploring its potential as a myokine and its interaction with NPs and NPR-C in the context of exercise-induced metabolic responses.

METHODS

Twenty-one inactive young males participated, and we assessed changes in serum levels of musclin, atrial natriuretic peptide (ANP), brain natriuretic peptide, epinephrine, and glycerol as indicative of lipid mobilization, during and after moderate-intensity aerobic exercise. Furthermore, we evaluated the gene expression of NPR-C in subcutaneous fat biopsies.

RESULTS

Serum musclin levels increased significantly during aerobic exercise, followed by a decline during recovery, remaining elevated compared to baseline. Significant correlations were found between musclin responses and lean body mass (LBM), indicating its regulation by skeletal muscle mass and exercise. Exercise-induced changes in musclin positively correlated with those of ANP, potentially preventing ANP degradation. Additionally, a potential interplay between NPR-C expression and musclin dynamics on ANP was suggested. However, musclin's influence on lipid mobilization was not predominant when considering other lipolytic factors during exercise.

DISCUSSION

Musclin's classification as a myokine is supported by its response to aerobic exercise and its association with LBM. Additionally, its interactions with NPR-C and NPs suggest its physiological relevance and potential clinical implications.

Metabolic Flexibility as a Candidate Mechanism for the Development of Postoperative Morbidity

BACKGROUND

This study investigates the role of metabolic flexibility in determining perioperative outcomes. Metabolic flexibility, a key feature of metabolic health, is the ability to efficiently switch between different fuel sources (predominantly carbohydrates and fats) depending on energy demands and availability. Given the rapidly changing physiological conditions in the perioperative period, we hypothesized that good metabolic adaptability could mitigate postoperative complications.

METHODS

We conducted a retrospective observational study utilizing a prospectively collected, single-center preoperative cardiopulmonary exercise testing (CPET) database of patients undergoing a range of major surgeries between 2012 and 2022. On day 3, patients were categorized into 3 groups based on their Postoperative Morbidity Survey (POMS) scores: 0 to 1, 2, and 3 to 6. Metabolic flexibility was evaluated through measurements of fat and carbohydrate oxidation during exercise testing (CPET). Associations were explored between metabolic flexibility, cardiorespiratory fitness, and postoperative outcomes.

RESULTS

Of 585 patients, those with no or low postoperative day 3 morbidity (POMS 0-1; n = 204) demonstrated significantly higher fat oxidation early in exercise before anaerobic threshold (fatty acid oxidation [FATox] area under the curve [AUC] 826 [578-1147]) compared to both POMS 2 (658 [448-922; n = 268]) and POMS 3 to 6 (608 [414-845; n = 113]); both P < .001. POMS 0 to 1 patients also had more effective carbohydrate utilization at peak exercise intensity. Higher postoperative morbidity (POMS) categories were associated with diminished metabolic flexibility characterized by a reduced ability to switch between metabolic substrates-carbohydrate oxidation (CHOox) POMS 0 to 1 group AUC 10277 (interquartile range [IQR] 7773-13358) compared to POMS 2 AUC 8356 (IQR 6548-10377) and POMS 3 to 6 AUC 6696 (IQR 473-9392); both P < .001. Reduced metabolic flexibility correlated with increased postoperative complications and an extended hospital stay.

CONCLUSIONS

Metabolic flexibility may be a pivotal factor in determining postoperative outcomes. Patients with greater metabolic adaptability had fewer complications and shorter hospitalization by 4 days on average. This suggests that preoperative metabolic conditioning-something potentially achieved by targeted prehabilitation-could be linked to surgical recovery. Future research should focus on prospective studies to confirm these relationships and explore underlying mechanisms. If confirmed, metabolic flexibility assessments could be integrated into routine preoperative evaluation to better predict and improve patient outcomes.

Comparison of Combined Motor Control Training and Isolated Extensor Strengthening Versus General Exercise on Lumbar Paraspinal Muscle Health and Associations With Patient-Reported Outcome Measures in Chronic Low Back Pain Patients: A Randomized Controlled Trial

Study DesignProspective Randomized Controlled Trial.ObjectivesTo investigate the effect of combined motor control and isolated lumbar strengthening exercise (MC + ILEX) vs general exercise (GE) on upper lumbar paraspinal muscle volume and composition, strength and patient outcomes in individuals with chronic low back pain (LBP).Methods50 participants with nonspecific chronic LBP were randomly allocated (1:1) to each group (MC + ILEX or GE) and underwent a 12-week supervised intervention program 2 times per week. Magnetic resonance imaging was performed at baseline, 6-weeks and 12-weeks to examine the impact of each intervention on multifidus (MF) and erector spinae (ES) muscle volume (cm3) and fatty infiltration (%FI) at L1-L2, L2-L3 and L3-L4.ResultsOur results revealed no significant between-groups findings for MF and ES %FI and volume, and patient-reported psychosocial measures. However, both groups had significant within-groups decreases in MF %FI at L1-L2, L2-L3 and L3-L4, with concomitant decreases in MF volume at L1-L2 and L2-L3, and at L3-L4 in the GE group. Each group displayed significant improvements in Kinesiophobia, while only MC + ILEX had significant improvements in pain catastrophizing, anxiety, depression and sleep. Lastly, significant correlations were found between change in Kinesiophobia and upper lumbar MF %FI, and between change in strength and lower lumbar MF and ES size.ConclusionsBoth exercise interventions may help reduce upper lumbar MF %FI in individuals with chronic LBP, while MC + ILEX could significantly improve important patient outcomes. Our results support the idea that improvements in paraspinal muscle health associate with better patient outcomes. Further high-quality imaging studies are needed to explore these relationships.

Charting the Molecular Terrain of Exercise: Energetics, Exerkines, and the Future of Multiomic Mapping

Physical activity plays a fundamental role in human health and disease. Exercise has been shown to improve a wide variety of disease states, and the scientific community is committed to understanding the precise molecular mechanisms that underlie the exquisite benefits. This review provides an overview of molecular responses to acute exercise and chronic training, particularly energy mobilization and generation, structural adaptation, inflammation, and immune regulation. Furthermore, it offers a detailed discussion of known molecular signals and systemic regulators activated during various forms of exercise and their role in orchestrating health benefits. Critically, the increasing use of multiomic technologies is explored with an emphasis on how multiomic and multitissue studies contribute to a more profound understanding of exercise biology. These data inform anticipated future advancement in the field and highlight the prospect of integrating exercise with pharmacology for personalized disease prevention and treatment.

Type 2 diabetes mellitus' impact on heart failure patients' exercise tolerance: a focus on maximal fat oxidation during exercise

Objective

To explore the impact of type 2 diabetes mellitus (T2DM) on exercise tolerance and fat oxidation capacity in patients with heart failure (HF).

Methods

We retrospectively analyzed 108 Chinese patients with HF who were divided into a diabetic group (T2DM group, n = 47) and a non-diabetic group (non-T2DM group, n = 61). All subjects completed cardiopulmonary exercise testing (CPX). We determined their fat oxidation (FATox) by indirect calorimetry.

Results

In the HF patients, the peak oxygen uptake (VO2) value was 14.76 ± 3.27 ml/kg/min in the T2DM group and 17.76 ± 4.64 ml/kg/min in the non-T2DM group. After adjusting for age, sex, body mass index (BMI), log N-terminal pro-B type natriuretic peptide (log NT-proBNP), left ventricular ejection fraction (LVEF), hemoglobin, renal function, coronary heart disease and hypertension, the peak VO2 was lower in the T2DM group compared to the non-T2DM group with a mean difference (MD) of -2.0 ml/kg/min [95% confidence interval (CI), -3.18 to -0.82, P < 0.01]. The VO2 at anaerobic threshold (AT VO2) was also lower in the T2DM group than in the non-T2DM group, with a MD of -1.11 ml/kg/min (95% CI -2.04 to -0.18, P < 0.05). Regarding the fat oxidation capacity during CPX, the T2DM group's maximal fat oxidation (MFO) was lower than that of the non-T2DM group (0.143 ± 0.055 vs. 0.169 ± 0.061 g/min, P < 0.05). In addition, the T2DM group had lower FATox at exercise intensity levels of 40% (P < 0.05) and 50% (P < 0.05) of peak VO2, compared to the non-T2DM group.

Conclusions

T2DM is associated with a decrease in exercise tolerance and fat oxidation capacity in patients with heart failure. Thus, it could be useful to develop exercises of appropriate intensity to optimize physical and metabolic health.

Effects of exercise on high-density lipoprotein levels in middle-aged and older individuals: A systematic review and meta-analysis

BACKGROUND

This study aimed to perform a systematic review and meta-analysis of randomized controlled trials investigating the effect of exercise on high-density lipoprotein (HDL) levels in middle-aged and older individuals.

METHODS

A systematic search was conducted in PubMed, Web of Science, and EMBASE, including meta-analyses of randomized controlled trials that investigated the effects of exercise on HDL-C levels in middle-aged and older individuals.

RESULTS

Forty-two trials were analyzed. We found that exercise had a significant effect on HDL cholesterol levels (standard mean difference [95% confidence interval] = 0.22 [0.09-0.35], Z = 3.28, P = .001, I2 = 54%), and the heterogeneity across the studies was significant and high. After subgroup analysis, we found that aerobic exercise had the most significant effect on the levels of HDLs in middle-aged and older individuals, which was better than that of other types of exercise.

CONCLUSIONS

Aerobic exercise significantly improves HDL levels in middle-aged and older individuals, but resistance and stretching exercises had no significant effect on HDL levels.

Tissue-specific and spatially dependent metabolic signatures perturbed by injury in skeletally mature male and female mice

Joint injury is a risk factor for post-traumatic osteoarthritis. However, metabolic and microarchitectural changes within the joint post-injury in both sexes remain unexplored. This study identified tissue-specific and spatially-dependent metabolic signatures in male and female mice using matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) and LC-MS metabolomics. Male and female C57Bl/6J mice were subjected to non-invasive joint injury. Eight days post-injury, serum, synovial fluid, and whole joints were collected for metabolomics. Analyses compared between injured, contralateral, and naïve mice, revealing local and systemic responses. Data indicate sex influences metabolic profiles across all tissues, particularly amino acid, purine, and pyrimidine metabolism. MALDI-MSI generated 2D ion images of bone, the joint interface, and bone marrow, highlighting increased lipid species in injured limbs, suggesting physiological changes across injured joints at metabolic and spatial levels. Together, these findings reveal significant metabolic changes after injury, with notable sex differences.

Optimal calorie restriction threshold: effect of FATmax exercise combined with different proportions of calorie restriction on hypercholesterolemia

Background/Objectives

To evaluate the impact of maximal fat oxidation intensity exercise combined with calorie restriction intervention on lipid-related parameters in a hypercholesterolemic population, and to determine if an optimal range of calorie restriction exists for effectively enhancing blood lipid profiles.

Methods

A 4-week intervention study combined exercise and calorie restriction for 64 patients aged 18-60 with secondary hypercholesterolemia. Ultimately, 43 participants completed the study. The dietary intervention adhered to the principles of a balanced diet, with meal plans designed to provide three meals per day for the duration of the study. Each subject's daily calorie intake was set to match their individual resting energy expenditure (REE) plus varying proportions of physical activity (PA) calories. Participants were divided into four groups based on these proportions: REE only, REE + PA33%, REE + PA67%, and REE + PA100%. FATmax exercises were conducted 5 times per week, lasting 1 h each.

Results

1) Compared with baseline, subjects' body weight, fat mass and body fat rate decreased significantly; fat-free mass also decreased significantly in the REE, REE + PA33%, and REE + PA67% groups. 2) Subjects' serum TC decreased significantly; serum LDL-C and ApoB decreased significantly in the REE, REE + PA33%, and REE + PA67% groups; there were no significant changes in serum HDL-C and ApoA1. 3) Serum PCSK9 was significantly decreased in the REE and the REE + PA 67% groups; serum LDLR was significantly decreased in all groups of subjects. 4) Between the groups, the rate of change in serum LDL-C was significantly different.

Conclusion

FATmax exercise combined with proper proportions of calorie restriction can significantly decrease serum cholesterol levels and fat mass in hypercholesterolemic patients. Nevertheless, it is misleading to assume that a drastic reduction in calorie intake invariably results in superior outcomes. Optimal cost-effectiveness may be achieved within a calorie restriction range of REE + PA33-67%.

The type of sport, but not sex, impacts body composition and metabolic response to a complete weight loss-weight regain episode in weight cycling athletes: results from the WAVE study

Athletes may engage in weight cycling-successive episodes of weight loss and weight (re)gain-for performance reasons, but risk metabolic adaptations and regaining more fat that was lost (fat overshoot). This study aimed to assess the influence of a complete weight cycling episode on body composition, thermoregulation, and metabolism in athletes, considering sex and the type of sport practiced. Forty-eight athletes (28 males, 20 females) engaged in combat (n = 23), strength (n = 12), or endurance (n = 13) sports were examined under three experimental conditions (weight maintenance, weight loss, weight (re)gain) during a weight cycling episode using their habitual strategies. Body composition (dual-energy X-ray absorptiometry), core body temperature (telemetric temperature sensor), energy expenditure and substrate oxidation at rest and during moderate exercise (indirect calorimetry), and energy intake (48 h food record) were assessed. Overall, athletes lost 4.4 ± 2.3% body weight, 12.2 ± 10.6% fat mass, and 2.6 ± 2.3% fat-free mass (p < 0.001). All variables returned to baseline values during the regain period, and a higher fat mass regain was observed in endurance than combat athletes (p < 0.01). During weight loss, a transient increase in lipid and decrease in carbohydrate oxidation occurred at rest and during exercise (p < 0.001). Energy expenditure and core body temperature remained unchanged across the three experimental conditions, and no specific sex effect was observed. Overall, no apparent body weight nor fat overshoot was observed in athletes after a complete weight cycling episode. Nonetheless, the greater fat mass gain in endurance, compared with combat athletes, highlights a need for further specific long-term studies in this population. Clinical Trial registration: NCT04107545.

Sex-specific differences in insulin response and substrate oxidation after repeated, brief whole-body immersion in 45 °C water: A prospective, interventional study

Prolonged heat exposure is suggested to improve glucose metabolism and fat oxidation, but no studies have addressed whether brief heat stimuli represent a viable, time-efficient, alternative approach. Consequently, we examined the ability of brief stimuli evoked by 45 °C water to improve glucose tolerance, insulin sensitivity, and fat oxidation in young, non-obese, males and females. Twenty-four participants completed fourteen 5-min sessions involving whole body passive heating in 45 °C water. Changes in resting catecholamines, cytokines, substrate oxidation, resting energy expenditure, glucose tolerance, and insulin release in response to an oral glucose tolerance test, were assessed before and 24-h after intervention, and 1 month after the end of the intervention. The results showed that repeated short-duration heat intervention had no significant effects on epinephrine, norepinephrine, interleukin-6, and tumor necrosis factor alpha production in both sexes. Glucose area under the curve (AUC) was not affected. However, females had a lower insulin AUC and improved insulin sensitivity as indicated by a decrease in homeostatic model assessment for insulin resistance, and an increase in the quantitative insulin sensitivity check index and the Matsuda insulin sensitivity index values one month after the end of the heat intervention. No effect was observed in resting energy expenditure, but carbohydrate oxidation per kilogram increased in females, and this substrate oxidation change was maintained after one month. In conclusion, fourteen sessions of brief 5-min whole-body immersion in 45 °C water produced an improvement in insulin sensitivity and increased reliance on carbohydrate oxidation in females.

Does mental exertion during incremental exercise change substrate oxidation and cardiorespiratory outcomes in individuals with overweight?

Given the growing concern over the impact of brain health in individuals with overweight, understanding how mental exertion (ME) during exercise affects substrate oxidation and cardiorespiratory outcomes is crucial. This study examines how ME impacts these outcomes during an incremental exercise test in adults with overweight. Seventeen adults who were overweight completed an incremental exercise test on a cycle ergometer two times, with and without the Stroop task. Energy expenditure (EE), carbohydrate and fat oxidation, maximum heart rate (HRmax), maximal oxygen uptake (VO2max), maximum fat oxidation (MFO), and the intensity of exercise that elicited MFO (Fatmax) are measured by indirect calorimetry. ME did not change the EE, carbohydrate, and fat oxidation at any stages of the incremental test. However, ME resulted in significantly lower HRmax, VO2max, and MFO (p < 0.01) and increased NASA-TLX scores but showed no change in Fatmax. These results show ME decreases the value of HRmax, VO2max, and MFO during the incremental exercise test. Due to the increased mental workload demonstrated by the NASA-TLX test, adults with overweight are unable to complete the test to the same extent as they did in the test without ME according to maximal levels in this study.

Circadian Regulation of Fatty Acid Metabolism in Humans: Is There Evidence of an Optimal Time Window for Maximizing Fat Oxidation During Exercise?

Exercise training performed at the intensity that elicits maximal fat oxidation improves cardiovascular function and metabolic health while simultaneously reducing visceral adipose tissue in patients with obesity and type 2 diabetes. Indeed, it is currently considered an efficient non-pharmacological approach for the prevention and treatment of cardiometabolic disorders. Over the last 5 years, several studies have reported a diurnal variation in both resting fat oxidation as well as maximal fat oxidation recorded during submaximal intensity exercise. Higher fat oxidation has been recorded during the evening in comparison with the early morning, although this has not been universally observed. If evening exercise increases fat oxidation, then this timing of exercise may be preferable for the reversal of cardiometabolic diseases. However, the physiological and molecular mechanisms behind the circadian regulation of fatty acid metabolism have not yet been fully elucidated. The present review thus aims to describe the circadian rhythmicity of several hormones, metabolites, and enzymes involved in fatty acid mobilization and oxidation. Furthermore, we discuss the relevance of circadian mitochondrial dynamics and oxidative phosphorylation to fatty acid metabolism. To conclude our discussion, we highlight those biological (e.g., age and sex) and lifestyle factors (e.g., sleep quality/disturbances or physical activity) that potentially influence the circadian regulation of fatty metabolism and which therefore should be considered for a tailored exercise prescription.

Sex- and endurance training-mediated cardiovascular protection through lipids during exercise

Premenopausal women and endurance-trained individuals of either sex have reduced cardiovascular disease (CVD) risk. Endurance training shifts fuel selection towards fats to spare carbohydrates; interestingly, women prioritize fats as an energy resource more than men do during exercise. Relying on fats during exercise drives whole-body lipolysis and promotes lipid uptake and oxidation capacity in skeletal muscles. These metabolic adaptations during exercise result in protection against diet-induced obesity, a healthy body fat distribution, and reduced plasma triacylglycerol (TG) concentrations. Here, we analyze how sex differences and endurance training mediate changes in skeletal muscles, including exercise-induced lipolysis, lipid uptake and β-oxidation, intramuscular TG storage, and postexercise lipid metabolism, and discuss how regulating this processes affects CVD risk.

Lower Plasma Lactate Concentrations After Training Support the Hypothesis of Improved Metabolic Flexibility in Male Long-Term Selected Marathon Mice Compared to Unselected Controls

Metabolic flexibility describes the capability to switch between oxidative fuels depending on their availability during diet or exercise. In a previous study, we demonstrated that in response to training, marathon (DUhTP) mice, paternally selected for high treadmill performance, are metabolically more flexible than unselected control (DUC) mice. Since exercise-associated metabolic flexibility can be assessed by indirect calorimetry or partially by circulating lactate concentrations, we investigated these parameters in DUhTP and DUC mice. Therefore, males of both lines completed a three-week high-speed treadmill training or were physically inactive (sedentary) before being placed in a metabolic cage for three days (one day of acclimatization, two days with monitoring), measuring CO2 and O2 to calculate respiratory quotient (RQ) and fatty acid oxidation (FATox). Circulating blood lactate concentrations were determined. Training resulted in a lower RQ in DUhTP and an increased RQ in DUC mice compared to their sedentary counterparts. Increased FATox rates and lower lactate concentrations were observed in exercised DUhTP but not in DUC mice, indicating a shift to oxidative metabolism in DUhTP and a glycolytic one in DUC mice. Therefore, improved metabolic flexibility in DUhTP mice is verifiable up to three days after training.

Metabolic phenotypes reflect patient sex and injury status: A cross-sectional analysis of human synovial fluid

OBJECTIVE

Osteoarthritis is a heterogeneous disease. The objective was to compare differences in underlying cellular mechanisms and endogenous repair pathways between synovial fluid (SF) from male and female participants with different injuries to improve the current understanding of the pathophysiology of downstream post-traumatic osteoarthritis (PTOA).

DESIGN

SF from n = 33 knee arthroscopy patients between 18 and 70 years with no prior knee injuries was obtained pre-procedure and injury pathology assigned post-procedure. SF was extracted and analyzed via liquid chromatography-mass spectrometry metabolomic profiling to examine differences in metabolism between injury pathologies (ligament, meniscal, and combined ligament and meniscal) and patient sex. Samples were pooled and underwent secondary fragmentation to identify metabolites.

RESULTS

Different knee injuries uniquely altered SF metabolites and downstream pathways including amino acid, lipid, and inflammatory-associated metabolic pathways. Notably, sexual dimorphic metabolic phenotypes were examined between males and females and within injury pathology. Cervonyl carnitine and other identified metabolites differed in concentrations between sexes.

CONCLUSIONS

These results suggest that different injuries and patient sex are associated with distinct metabolic phenotypes. Considering these phenotypic associations, a greater understanding of metabolic mechanisms associated with specific injuries, sex, and PTOA development may yield data regarding how endogenous repair pathways differ between male and female injury types. Ongoing metabolomic analysis of SF in injured male and female patients can be performed to monitor PTOA development and progression.

The Effect of Time-Restricted Eating Combined with Exercise on Body Composition and Metabolic Health: A Systematic Review and Meta-Analysis

BACKGROUND

Time-restricted eating (TRE) is increasingly popular, but its benefits in combination with exercise still need to be determined.

OBJECTIVES

This systematic review and meta-analysis aimed to evaluate the efficacy of TRE combined with exercise compared with control diet with exercise in improving the body composition and metabolic health of adults.

METHODS

Five electronic databases were searched for relevant studies. Randomized controlled trials (RCTs) examining the effect of TRE combined with exercise on body composition and metabolic health in adults were included. All results in the meta-analysis are reported as mean difference (MD) with 95% confidence interval (CI). Study quality was assessed using the revised Cochrane Risk of Bias Tool and Grading of Recommendations Assessment, Development, and Evaluation assessment.

RESULTS

In total, 19 RCTs comprising 568 participants were included in this systematic review and meta-analysis. TRE combined with exercise likely reduced the participants' body mass (MD: -1.86 kg; 95% CI: -2.75, -0.97 kg) and fat mass (MD: -1.52 kg; 95% CI: -2.07, -0.97 kg) when compared with the control diet with exercise. In terms of metabolic health, the TRE combined with exercise group likely reduced triglycerides (MD: -13.38 mg/dL, 95% CI: -21.22, -5.54 mg/dL) and may result in a reduction in low-density lipoprotein (MD: -8.52 mg/dL; 95% CI: -11.72, -5.33 mg/dL) and a large reduction in leptin (MD: -0.67 ng/mL; 95% CI: -1.02, -0.33 ng/mL). However, TRE plus exercise exhibited no additional benefit on the glucose profile, including fasting glucose and insulin, and other lipid profiles, including total cholesterol and high-density lipoprotein concentrations, compared with the control group.

CONCLUSIONS

Combining TRE with exercise may be more effective in reducing body weight and fat mass and improving lipid profile than control diet with exercise. Implementing this approach may benefit individuals aiming to achieve weight loss and enhance their metabolic well-being. This study was registered in PROSPERO as CRD42022353834.

The characterization of metabolic changes in adipose tissues and muscles due to different exercise intensities by Dixon in healthy young men

PURPOSE

To delineate the alterations in adipose and muscle tissue composition and functionality among healthy young men across varying exercise intensities, which help to elucidate the impact of exercise intensity on weight management and inform fitness planning.

METHOD

3D Dixon MRI scans were performed on the neck and supraclavicular area in 10 high-intensity exercises (HIE) athletes, 20 moderate intensity exercises (MIE) athletes and 19 low-intensity exercises non-athlete male controls (NCM). Twelve imaging parameters, including the total volume of muscle, white adipose tissue (WAT), brown adipose tissue (BAT), and the mean fat-water fraction (FWF) within these tissues. Additionally, ratios of BAT or WAT to total fat (BATr or WATr) and the proportions of muscle, BAT, or WAT to total tissue volume (Musp, BATp, and WATp) were calculated. Parameters were compared across groups and correlated with Body Mass Index (BMI), waistline, and hipline.

RESULTS

The HIE group exhibited the highest total muscle (totalMUS) and brown adipose tissue (totalBAT) volumes among the three groups. Conversely, the NCM group had significantly higher fwfFAT and fwfBAT values. The MUSp was higher in the HIE and MIE groups compared to NCM, while the BATp and WATp were lower. Furthermore, the BATr in HIE and MIE groups were higher than NCM group while the WATr were lower. Significant linear relationships were observed between totalBAT, totalWAT, MUSp, BATr, fwfFAT, and BMI, waistline (P < 0.05) across all groups.

CONCLUSIONS

MIE is sufficient for the purpose of weight control, While HIE helps to further increase the muscle mass. All three physical indexes were significantly associated with the image parameters, with waistline emerging as the most effective indicator for detecting metabolic changes across all groups.

Metabolic flexibility in postmenopausal women: Hormone replacement therapy is associated with higher mitochondrial content, respiratory capacity, and lower total fat mass

AIM

To investigate effects of hormone replacement therapy in postmenopausal women on factors associated with metabolic flexibility related to whole-body parameters including fat oxidation, resting energy expenditure, body composition and plasma concentrations of fatty acids, glucose, insulin, cortisol, and lipids, and for the mitochondrial level, including mitochondrial content, respiratory capacity, efficiency, and hydrogen peroxide emission.

METHODS

22 postmenopausal women were included. 11 were undergoing estradiol and progestin treatment (HT), and 11 were matched non-treated controls (CONT). Peak oxygen consumption, maximal fat oxidation, glycated hemoglobin, body composition, and resting energy expenditure were measured. Blood samples were collected at rest and during 45 min of ergometer exercise (65% VO2peak). Muscle biopsies were obtained at rest and immediately post-exercise. Mitochondrial respiratory capacity, efficiency, and hydrogen peroxide emission in permeabilized fibers and isolated mitochondria were measured, and citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HAD) activity were assessed.

RESULTS

HT showed higher absolute mitochondrial respiratory capacity and post-exercise hydrogen peroxide emission in permeabilized fibers and higher CS and HAD activities. All respiration normalized to CS activity showed no significant group differences in permeabilized fibers or isolated mitochondria. There were no differences in resting energy expenditure, maximal, and resting fat oxidation or plasma markers. HT had significantly lower visceral and total fat mass compared to CONT.

CONCLUSION

Use of hormone therapy is associated with higher mitochondrial content and respiratory capacity and a lower visceral and total fat mass. Resting energy expenditure and fat oxidation did not differ between HT and CONT.

Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine-A Narrative Review

Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine's ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine's indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.

Disuse-Induced Muscle Fatigue: Facts and Assumptions

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, "oxidative" "slow" phenotype to a "fast" "glycolytic" one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue.

Effects of 24-week Polarized Training vs. Threshold Training in Obese Male Adults

The combination of high volume of moderate-intensity continuous training with a low volume of high-intensity interval training improved body composition and physical capacities in individuals with obesity. However, polarized training (POL) has never been used in adult men with obesity. Thus, the purpose of this study was to investigate changes in body composition and physical capacities induced by a 24-week POL or threshold (THR) program in obese male adults. Twenty male patients (mean age 39.8±6.3 yrs; mean body mass index [BMI] 31.6±2.7 kg∙m-2) participated in this study (n: 10 POL, n: 10 THR). After 24-week, body mass (BM) and fat mass (FM) decreased by -3.20±3.10 kg (P<0.05) and -3.80±2.80 kg (P<0.05), respectively, similarly in both groups. Maximal oxygen uptake (  ̇VO2max) and   ̇VO2 at respiratory compensation point (RCP) increased in the POL group (+8.5±12.2 and+9.0±17.0%, P<0.05) and in the THR group (+4.24±8.64 and+4.0±6.70%, P<0.05), as well   ̇VO2 at gas exchange threshold (GET) increased similarly in both groups (+12.8±12.0%, P<0.05). POL and THR were equally effective in improving body composition and physical capacities in obese subjects. Future studies are needed to determine whether adherence to the training program can be improved by adding a running competition compared with a group without competition at the end of the training program.

Heat stress increases carbohydrate oxidation rates and oxygen uptake during prolonged load carriage exercise

Military missions are conducted in a multitude of environments including heat and may involve walking under load following severe exertion, the metabolic demands of which may have nutritional implications for fueling and recovery planning. Ten males equipped a military pack loaded to 30% of their body mass and walked in 20°C/40% relative humidity (RH) (TEMP) or 37°C/20% RH (HOT) either continuously (CW) for 90 min at the first ventilatory threshold or mixed walking (MW) with unloaded running intervals above the second ventilatory threshold between min 35 and 55 of the 90 min bout. Pulmonary gas, thermoregulatory, and cardiovascular variables were analyzed following running intervals. Final rectal temperature (MW: p < 0.001, g = 3.81, CW: p < 0.001, g = 4.04), oxygen uptake, cardiovascular strain, and energy expenditure were higher during HOT trials (p ≤ 0.05) regardless of exercise type. Both HOT trials elicited higher final carbohydrate oxidation (CHOox) than TEMP CW at min 90 (HOT MW: p < 0.001, g = 1.45, HOT CW: p = 0.009, g = 0.67) and HOT MW CHOox exceeded TEMP MW at min 80 and 90 (p = 0.049, g = 0.60 and p = 0.024, g = 0.73, respectively). There were no within-environment differences in substrate oxidation indicating that severe exertion work cycles did not produce a carryover effect during subsequent loaded walking. The rate of CHOox during 90 minutes of load carriage in the heat appears to be primarily affected by accumulated thermal load.

Genetics of Exercise and Diet-Induced Fat Loss Efficiency: A Systematic Review

Physical exercise and dieting are well-known and effective methods for fat loss and improving cardiovascular health. However, different individuals often react differently to the same exercise regimen or dietary plan. While specific individuals may undergo substantial fat loss, others may observe only limited effects. A wide range of inter-individual variability in weight gain and changes in body composition induced by physical exercises and diets led to an investigation into the genetic factors that may contribute to the individual variations in such responses. This systematic review aimed at identifying the genetic markers associated with fat loss resulting from diet or exercise. A search of the current literature was performed using the PubMed database. Forty-seven articles met the inclusion criteria when assessing genetic markers associated with weight loss efficiency in response to different types of exercises and diets. Overall, we identified 30 genetic markers of fat-loss efficiency in response to different kinds of diets and 24 in response to exercise. Most studies (n = 46) used the candidate gene approach. We should aspire to the customized selection of exercise and dietary plans for each individual to prevent and treat obesity.

The influence of cardiorespiratory fitness level on the relationship between work rates at the aerobic threshold (AerT) and the point of maximal fat oxidation (Fatmax) in untrained adults

Introduction

In this study, we investigated the impact of cardiorespiratory fitness (CRF), quantified as peak oxygen consumption (VO2peak), on the relationship between work rates (WR) at the aerobic threshold (AerT) and the point of maximal fat oxidation rate (Fatmax).

Methods

A total of 761 untrained adults aged 41-68 completed a one-minute incremental exercise test on a cycle ergometer, using breath-by-breath gas analysis to determine VO2peak, AerT, and Fatmax. AerT was determined using automatic and visual detection methods, and Fatmax was determined using indirect calorimetry. Participants were categorized into CRF-groups: low (<25th percentile), medium (≥25th percentile and <75th percentile), and high (≥75th percentile).

Results

Fatmax was found at 43 ± 7% WRpeak, 37% ± 6% WRpeak and 35% ± 7% WRpeak in the low, medium, and high CRF-groups, respectively. In contrast, AerT was located at significantly higher relative work rates: 51% ± 8% WRpeak, 47% ± 10% WRpeak, and 47% ± 11% WRpeak in the respective CRF-groups. There was a weak agreement between Fatmax and AerT [intraclass correlation coefficient (ICC) = .19, p < .001], and the ICC decreased from .35 to .12 to .13, while the mean bias ±95% limits of agreement increased from 8% ± 14% WRpeak to 8% ± 19% WRpeak to 12% ± 44% WRpeak from CRF-low to CRF-medium to CRF-high. The mean difference between Fatmax and AerT was significantly different among the CRF subgroups: 8% ± 7% WRpeak vs. 10% ± 10% WRpeak vs. 12% ± 11% WRpeak in low, medium, and high CRF-groups, respectively. Nonetheless, multiple regression analysis revealed only a weak positive correlation between the difference in relative work rates (% WRpeak) between Fatmax and AerT (dependent variable) and the predictor variables CRF and sex, both identified as significant (R = .19, p < .001).

Conclusion

Our study confirms substantial differences in exercise intensities between Fatmax and AerT in untrained adults (10% ± 19% WRpeak, ranging from -14% to 53% WRpeak). Importantly, this difference remains relatively consistent across varying CRF levels, emphasizing the distinct nature of Fatmax and AerT, with CRF playing a limited role in influencing their relationship in our study's untrained adults.

Indirect Calorimetry-Based Novel Approach for Evaluating Metabolic Flexibility and Its Association with Circulating Metabolic Markers in Middle-Aged Subjects

We propose a novel method for assessing metabolic flexibility (MF) through indirect calorimetry. A total of twenty healthy volunteers (10 females; 10 males) aged 45-65 were categorized into a Low-Intensity activity group (LI, 0-1 session of 1 h per week) and a High-Intensity activity group (HI, 5-6 sessions of 2 h per week). Volunteers underwent a stepwise exercise test on a cycle ergometer, connected to a calorimeter, to examine respiratory gas exchange to evaluate peak fatty acid Oxidation (PFO) and peak carbohydrate oxidation (PCO). Circulating peroxisome proliferator-activated receptor α (PPARα) biomarkers, docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) ratio and N-oleoylethanolamine (OEA), and the endocannabinoid- 2-arachidonoylglycerol (2-AG), were evaluated. We developed two MF parameters: the MF index (MFI), calculated by the product of PFO normalized per kg of fat-free mass (FFM) and the percentage of VO2max at PFO, and the peak energy substrates' oxidation (PESO), computed by summing the kilocalories from the PFO and PCO, normalized per kg FFM. The MFI and PESO were significantly different between the HI and LI groups, showing strong correlations with the circulating bioactive substances. Higher DHA/EPA ratio (p ≤ 0.05) and OEA (p ≤ 0.01), but lower 2-AG levels (p ≤ 0.01) were found in the HI group. These new parameters successfully established a functional link between MF and the balance of PPARα/endocannabinoid systems.

The role of GPR81-cAMP-PKA pathway in endurance training-induced intramuscular triglyceride accumulation and mitochondrial content changes in rats

The athlete's paradox phenomenon involves the accumulation of intramuscular triglycerides (IMTG) in both insulin-resistant and insulin-sensitive endurance athletes. Nevertheless, a complete understanding of this phenomenon is yet to be achieved. Recent research indicates that lactate, a common byproduct of physical activity, may increase the accumulation of IMTG in skeletal muscle. This is achieved through the activation of G protein-coupled receptor 81 (GPR81) leads to the suppression of the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway. The mechanism accountable for the increase in mitochondrial content in skeletal muscle triggered by lactate remains incomprehensible. Based on current research, our objective is to explore the role of the GPR81-inhibited cAMP-PKA pathway in the aggregation of IMTG and the increase in mitochondrial content as a result of prolonged exercise. The GPR81-cAMP-PKA-signaling pathway regulates the buildup of IMTG caused by extended periods of endurance training (ET). This is likely due to a decrease in proteins related to fat breakdown and an increase in proteins responsible for fat production. It is possible that the GPR81-cAMP-PKA pathway does not contribute to the long-term increase in mitochondrial biogenesis and content, which is induced by chronic ET. Additional investigation is required to explore the possible hindrance of the mitochondrial biogenesis and content process during physical activity by the GPR81-cAMP-PKA signal.

Follistatin-like 1 is a myokine regulating lipid mobilization during endurance exercise and recovery

OBJECTIVE

The aim of this study was to investigate the role of the follistatin-like 1 (Fstl1) and disco-interacting protein 2 homolog A (DIP2a) axis in relation to lipid metabolism during and after endurance exercise and to elucidate the mechanisms underlying the metabolic effects of Fstl1 on adipocytes, considering its regulation by exercise and muscle mass and its link to obesity.

METHODS

Twenty-nine sedentary males participated in endurance exercise, and blood samples were collected during and after the exercise. Body composition, Fstl1, glycerol, epinephrine, growth hormone, and atrial natriuretic peptide were measured. 3T3-L1 adipocytes, with or without DIP2a knockdown, were treated with Fstl1 to assess glycerol release, cyclic AMP/cyclic GMP production, and hormone sensitive lipase phosphorylation. The association between DIP2a gene expression levels in human adipose tissues and exercise-induced lipolysis was examined.

RESULTS

Fstl1 levels significantly increased during endurance exercise and following recovery, correlating with lean body mass and lipolysis. In 3T3-L1 adipocytes, Fstl1 increased glycerol release, cyclic GMP production, and hormone sensitive lipase activation, but these effects were attenuated by DIP2a knockdown. DIP2a gene expression in human adipose tissues correlated with serum glycerol concentrations during endurance exercise.

CONCLUSIONS

Fstl1 is a myokine facilitating lipid mobilization during and after endurance exercise through DIP2a-mediated lipolytic effects in adipocytes.

Effect of Acute Caffeine Intake on Fat Oxidation Rate during Fed-State Exercise: A Systematic Review and Meta-Analysis

Pre-exercise intake of caffeine (from ~3 to 9 mg/kg) has been demonstrated as an effective supplementation strategy to increase fat oxidation during fasted exercise. However, a pre-exercise meal can alter the potential effect of caffeine on fat oxidation during exercise as caffeine modifies postprandial glycaemic and insulinemic responses. Hypothetically, the effect of caffeine on fat oxidation may be reduced or even withdrawn during fed-state exercise. The present systematic review aimed to meta-analyse investigations on the effect of acute caffeine intake on the rate of fat oxidation during submaximal aerobic exercise performed in the fed state (last meal < 5 h before exercise). A total of 18 crossover trials with randomised and placebo-controlled protocols and published between 1982 and 2021 were included, with a total of 228 participants (185 males and 43 females). Data were extracted to compare rates of fat oxidation during exercise with placebo and caffeine at the same exercise intensity, which reported 20 placebo-caffeine pairwise comparisons. A meta-analysis of the studies was performed, using the standardised mean difference (SMD) estimated from Hedges' g, with 95% confidence intervals (CI). In comparison with the placebo, caffeine increased the rate of fat oxidation during fed-state exercise (number of comparisons (n) = 20; p = 0.020, SMD = 0.65, 95% CI = 0.20 to 1.20). Only studies with a dose < 6 mg/kg of caffeine (n = 13) increased the rate of fat oxidation during fed-state exercise (p = 0.004, SMD = 0.86, 95% CI = 0.27 to 1.45), while no such effect was observed in studies with doses ≥6 mg/kg (n = 7; p = 0.97, SMD = -0.03, 95% CI = -1.40 to 1.35). The effect of caffeine on fat oxidation during fed-state exercise was observed in active untrained individuals (n = 13; p < 0.001, SMD = 0.84, 95% CI = 0.39 to 1.30) but not in aerobically trained participants (n = 7; p = 0.27, SMD = 0.50, 95% CI = -0.39 to 1.39). Likewise, the effect of caffeine on fat oxidation was observed in caffeine-naïve participants (n = 9; p < 0.001, SMD = 0.82, 95% CI = 0.45 to 1.19) but not in caffeine consumers (n = 3; p = 0.54, SMD = 0.57, 95% CI = -1.23 to 2.37). In conclusion, acute caffeine intake in combination with a meal ingested within 5 h before the onset of exercise increased the rate of fat oxidation during submaximal aerobic exercise. The magnitude of the effect of caffeine on fat oxidation during fed-state exercise may be modulated by the dose of caffeine administered (higher with <6 mg/kg than with ≥6 mg/kg), participants' aerobic fitness level (higher in active than in aerobically trained individuals), and habituation to caffeine (higher in caffeine-naïve than in caffeine consumers).

The effects of aerobic exercise on cardiometabolic health in postmenopausal females: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

After menopause, reductions in ovarian hormones increase the risk of cardiovascular disease. Aerobic exercise training has been shown to reduce cardiovascular risk in older adults, but its effectiveness in postmenopausal females is less definitive.

OBJECTIVES

The objectives of this study were to examine the: (1) effects of aerobic training, and (2) association between aerobic training intensity and cardiometabolic health outcomes in postmenopausal females.

DESIGN

Systematic review and meta-analysis of randomized controlled trials.

DATA SOURCES AND METHODS

Six electronic databases were searched from inception to July 21, 2023 for aerobic training interventions reporting cardiometabolic outcomes in postmenopausal females. Data were synthesized qualitatively and random-effects meta-analyses and subgroup analyses (light, moderate, and vigorous intensity) were performed. Grading of Recommendations, Assessment, Development and Evaluation was used to assess the certainty of evidence.

RESULTS

Fifty-nine studies (n = 4,225; 45-78 years old) were identified, 53 (n = 3,821) were included in the quantitative analyses. Aerobic training interventions varied in frequency (3-21×/week), intensity, type, time (8-60 min/session), and duration (3-52 weeks). Aerobic training improved systolic blood pressure (mean difference (MD) = -4.41 mmHg, 95% confidence interval (95%CI) [-7.29, -1.52], p = 0.01), resting heart rate (MD = -3.08 bpm, 95%CI [-5.11, -1.05], p < 0.01), body mass index (BMI, MD = -0.65 kg/m2, 95%CI [-0.99, -0.31], p < 0.01), waist circumference (MD = -2.03 cm, 95%CI [-2.65, -1.41], p < 0.01), body fat (MD = -2.57 kg, 95%CI [-3.65, -1.49], p < 0.01), low-density lipoprotein cholesterol (MD = -10.46 mg/dL, 95%CI [-16.31, -4.61], p < 0.01), high-density lipoprotein cholesterol (MD = 3.28 mg/dL, 95%CI [0.20, 6.36], p = 0.04) and cardiorespiratory fitness (standardized MD = 1.38, 95%CI [1.13, 1.64], p < 0.01). There was a very low certainty of evidence for all outcomes. In subgroup analyses, light- and vigorous intensities were beneficial for BMI with no effect for moderate-intensity exercise (p < 0.01). Light intensity showed a beneficial effect (p = 0.02) for glucose levels (p < 0.01) and triglycerides; there was no effect with moderate or vigorous intensities.

CONCLUSION

Aerobic training may improve cardiometabolic health outcomes in postmenopausal females. There may be differential effects of exercise intensity on BMI, blood triglycerides, and blood glucose; however, this warrants further investigation.

REGISTRATION

PROSPERO-CRD42022313350.

Fatty acid oxidation regulates cellular senescence by modulating the autophagy-SIRT1 axis

Senescence, a cellular process through which damaged or dysfunctional cells suppress the cell cycle, contributes to aging or age-related functional decline. Cell metabolism has been closely correlated with aging processes, and it has been widely recognized that metabolic changes underlie the cellular alterations that occur with aging. Here, we report that fatty acid oxidation (FAO) serves as a critical regulator of cellular senescence and uncover the underlying mechanism by which FAO inhibition induces senescence. Pharmacological or genetic ablation of FAO results in a p53-dependent induction of cellular senescence in human fibroblasts, whereas enhancing FAO suppresses replicative senescence. We found that FAO inhibition promotes cellular senescence through acetyl-CoA, independent of energy depletion. Mechanistically, increased formation of autophagosomes following FAO inhibition leads to a reduction in SIRT1 protein levels, thereby contributing to senescence induction. Finally, we found that inhibition of autophagy or enforced expression of SIRT1 can rescue the induction of senescence as a result of FAO inhibition. Collectively, our study reveals a distinctive role for the FAO-autophagy-SIRT1 axis in the regulation of cellular senescence. [BMB Reports 2023; 56(12): 651-656].

The effect of a short-term ketogenic diet on exercise efficiency during graded exercise in healthy adults

OBJECTIVE

We examined the effects of short-term KD on exercise efficiency and hormonal response during and after the graded exercise testing.

METHODS

Fourteen untrained healthy adults (8 males, 6 females, age 26.4 ± 3.1 [SD] years; BMI 24.8 ± 4.6 kg/m2; peak VO2max 54.0 ± 5.8 ml/kg FFM/min) completed 3-days of a mixed diet (MD) followed by another 3-days of KD after 3-days of washout period. Upon completion of each diet arm, participants underwent graded exercise testing with low- (LIE; 40% of VO2max), moderate- (MIE; 55%), and high-intensity exercise (HIE; 70%). Exercise efficiency was calculated as work done (kcal/min)/energy expenditure (kcal/min).

RESULTS

Fat oxidation during the recovery period was higher in KD vs. MD. Despite identical workload during HIE, participants after having KD vs. MD showed higher energy expenditure and lower exercise efficiency (10.1 ± 0.7 vs. 12.5 ± 0.3%, p < .01). After KD, free fatty acid (FFA) concentrations were higher during MIE and recovery vs. resting, and beta-hydroxybutylate (BOHB) was lower at HIE vs. resting. Cortisol concentrations after KD was higher during recovery vs. resting, with no significant changes during graded exercise testing after MD.

CONCLUSIONS

Our data suggest that short-term KD is favorable to fat metabolism leading increased circulating FFA and BOHB during LIE to MIE. However, it is notable that KD may cause 1) exercise inefficiency manifested by increased energy expenditure and 2) elevated exercise stress during HIE and recovery. Trial registration: KCT0005172, International Clinical Trials Registry Platform.

Maximal oxidative capacity during exercise is associated with muscle power output in patients with long coronavirus disease 2019 (COVID-19) syndrome. A moderation analysis

BACKGROUND & AIMS

Long COVID syndrome (LCS) involves persistent symptoms experienced by many patients after recovering from coronavirus disease 2019 (COVID-19). We aimed to assess skeletal muscle energy metabolism, which is closely related to substrate oxidation rates during exercise, in patients with LCS compared with healthy controls. We also examined whether muscle power output mediates the relationship between COVID-19 and skeletal muscle energy metabolism.

METHODS

In this cross-sectional study, we enrolled 71 patients with LCS and 63 healthy controls. We assessed clinical characteristics such as body composition, physical activity, and muscle strength. We used cardiopulmonary exercise testing to evaluate substrate oxidation rates during graded exercise. We performed statistical analyses to compare group characteristics and peak fat oxidation differences based on power output.

RESULTS

The two-way analysis of covariance (ANCOVA) results, adjusted for covariates, showed that the patients with LCS had lower absolute maximal fatty acid oxidation (MFO), relative MFO/fat free mass (FFM), absolute carbohydrates oxidation (CHox), relative CHox/FFM, and oxygen uptake (V˙˙O2) at maximum fat oxidation (g min-1) than the healthy controls (P < 0.05). Moderation analysis indicated that muscle power output significantly influenced the relationship between LCS and reduced peak fat oxidation (interaction β = -0.105 [95% confidence interval -0.174; -0.036]; P = 0.026). Therefore, when muscle power output was below 388 W, the effect of the LCS on MFO was significant (62% in our study sample P = 0.010). These findings suggest compromised mitochondrial bioenergetics and muscle function, represented by lower peak fat oxidation rates, in the patients with LCS compared with the healthy controls.

CONCLUSION

The patients with LCS had lower peak fat oxidation during exercise compared with the healthy controls, potentially indicating impairment in skeletal muscle function. The relationship between peak fat oxidation and LCS appears to be mediated predominantly by muscle power output. Additional research should continue investigating LCS pathogenesis and the functional role of mitochondria.

Fatty acid oxidation regulates cellular senescence by modulating the autophagy-SIRT1 axis

Senescence, a cellular process through which damaged or dysfunctional cells suppress the cell cycle, contributes to aging or age-related functional decline. Cell metabolism has been closely correlated with aging processes, and it has been widely recognized that metabolic changes underlie the cellular alterations that occur with aging. Here, we report that fatty acid oxidation (FAO) serves as a critical regulator of cellular senescence and uncover the underlying mechanism by which FAO inhibition induces senescence. Pharmacological or genetic ablation of FAO results in a p53-dependent induction of cellular senescence in human fibroblasts, whereas enhancing FAO suppresses replicative senescence. We found that FAO inhibition promotes cellular senescence through acetyl-CoA, independent of energy depletion. Mechanistically, increased formation of autophagosomes following FAO inhibition leads to a reduction in SIRT1 protein levels, thereby contributing to senescence induction. Finally, we found that inhibition of autophagy or enforced expression of SIRT1 can rescue the induction of senescence as a result of FAO inhibition. Collectively, our study reveals a distinctive role for the FAO-autophagy-SIRT1 axis in the regulation of cellular senescence. [BMB Reports 2023; 56(12): 651-656].

Effects of 12 Weeks of Family and Individual Multi-Disciplinary Intervention in Overweight and Obese Adolescents under Cardiometabolic Risk Parameters: A Clinical Trial

Adolescence is a complex period of human development in which young people are susceptible to unhealthy behaviors, such as physical inactivity and an unbalanced diet. This study aimed to analyze the effects of 12 weeks of multi-disciplinary family and individual intervention on cardiometabolic risk parameters in overweight and obese adolescents and compare sub-groups, considering possible differences between sexes (males vs. females vs. intervention approach). Forty-three adolescents (13.73 ± 2.46 years old) of both sexes were divided into two groups: family group (FG) (n = 21; 14.24 ± 2.61 years old) and individual group (IG) (n = 22; 13.23 ± 2.27 years old). The following parameters were evaluated: anthropometry (body weight, height, waist circumference (WC), hip circumference (HC), abdominal circumference (AC), calculation of body mass index (BMI), and waist-hip ratio (WHR)), body composition (fat mass (FM), lean mass (LM), fat-free mass (FFM), skeletal muscle mass (SMM), body fat percentage (BF), and visceral fat), biochemical measures (fasting glucose, triglycerides (TG), total cholesterol (TC), low-density lipoproteins (LDL-c), and high-density lipoproteins (HDL-c)), and the measurement of systolic and diastolic blood pressure (SBP and DBP) before and after the interventions. The multi-disciplinary interventions occurred for 12 weeks (three days a week lasting 1 h and 30 min, in which 30 min were dedicated to theoretical interventions (nutrition: nutritional education and psychology: psychoeducation) and 1 h to physical exercises. A time effect was observed for LM, FFM, SMM, FM, and HDL-c, with higher values after intervention and a significant decrease for FM, BF, visceral fat, fasting glucose, TG, TC, LDL-c, and DBP (p < 0.05). However, no group, sub-group, or interaction effects were observed when comparing FG, IG, or sexes (p > 0.05). The responses of the present study show that both multi-disciplinary approaches (family and individual) promoted improvement in the body composition indicators, biochemical markers, and DBP of overweight and obese adolescents independently of the intervention group. Given this finding, health professionals, families, and adolescents could choose the type of intervention based on their preferences.

Effects of combined training or moderate intensity continuous training during a 3-week multidisciplinary body weight reduction program on cardiorespiratory fitness, body composition, and substrate oxidation rate in adolescents with obesity

This study aimed to investigate the effects of combined training (COMB, a combination of moderate-intensity continuous training-MICT and high-intensity interval training-HIIT) vs. continuous MICT administered during a 3-week in-hospital body weight reduction program (BWRP) on body composition, physical capacities, and substrate oxidation in adolescents with obesity. The 3-week in-hospital BWRP entailed moderate energy restriction, nutritional education, psychological counseling, and two different protocols of physical exercise. Twenty-one male adolescents with obesity (mean age: 16.1 ± 1.5 years; mean body mass index [BMI] 37.8 ± 4.5 kg m-2) participated in this randomized control trial study (n:10 for COMB, n:11 MICT), attending ~ 30 training sessions. The COMB group performed 3 repetitions of 2 min at 95% of peak oxygen uptake (V'O2 peak) (e.g., HIIT ≤ 20%), followed by 30 min at 60% of V'O2 peak (e.g., MICT ≥ 80%). Body composition, V'O2 peak, basal metabolic rate (BMR), energy expenditure, and substrate oxidation rate were measured during the first week (W0) and at the end of three weeks of training (W3). The two training programs were equivalent in caloric expenditure. At W3, body mass (BM) and fat mass (FM) decreased significantly in both groups, although the decrease in BM was significantly greater in the MICT group than in the COMB group (BM: - 5.0 ± 1.2 vs. - 8.4 ± 1.5, P < 0.05; FM: - 4.3 ± 3.0 vs. - 4.2 ± 1.9 kg, P < 0.05). V'O2 peak increased only in the COMB by a mean of 0.28 ± 0.22 L min-1 (P < 0.05). The maximal fat oxidation rate (MFO) increased only in the COMB group by 0.04 ± 0.03 g min-1 (P < 0.05). COMB training represents a viable alternative to MICT for improving anthropometric characteristics, physical capacities, and MFO in adolescents with obesity during a 3-week in-hospital BWRP.

Chronic high-intensity interval training and moderate-intensity continuous training are both effective in increasing maximum fat oxidation during exercise in overweight and obese adults: A meta-analysis

Objective

to (1) systematically review the chronic effect of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on maximal fat oxidation (MFO) in overweight and obese adults, and (2) explore MFO influencing factors and its dose-response relationships with HIIT and MICT.

Methods

Studies using a between-group design involving overweight and obese adults and assessing the effect of HIIT and MICT on MFO were included. A meta-analysis on MFO indices was conducted, and the observed heterogeneities were explored through subgroup, regression, and sensitivity analyses.

Results

Thirteen studies of moderate to high quality with a total of 519 overweight and obese subjects were included in this meta-analysis (HIIT, n = 136; MICT, n = 235; Control, n = 148). HIIT displayed a statistically significant favorable effect on MFO compared to no-training (MD = 0.07; 95%CI [0.03 to 0.11]; I2 = 0%). Likewise, MICT displayed a statistically significant favorable effect on MFO compared to no-training (MD = 0.10; 95%CI [0.06 to 0.15]; I2 = 95%). Subgroup and regression analyses revealed that exercise intensity (Fatmax vs. non-Fatmax; %VO2peak), exercise mode, BMI, and VO2peak all significantly moderated MICT on MFO. When analyzing studies that have directly compared HIIT and MCIT in obese people, it seems there is no difference in the MFO change (MD = 0.01; 95%CI [-0.02 to 0.04]; I2 = 64%). No publication bias was found in any of the above meta-analyses (Egger's test p > 0.05 for all).

Conclusion

Both HIIT and MICT are effective in improving MFO in overweight and obese adults, and they have similar effects. MCIT with an intensity of 65-70% VO2peak, performed 3 times per week for 60 min per session, will optimize MFO increases in overweight and obese adults. Given the lack of studies examining the effect of HIIT on MFO in overweight and obese adults and the great diversity in the training protocols in the existing studies, we were unable to make sound recommendations for training.

The Effects of Combined Motor Control and Isolated Extensor Strengthening versus General Exercise on Paraspinal Muscle Morphology, Composition, and Function in Patients with Chronic Low Back Pain: A Randomized Controlled Trial

Low back pain (LBP), a globally widespread and persistent musculoskeletal disorder, benefits from exercise therapy. However, it remains unclear which type leads to greater changes in paraspinal muscle health. This study aimed to (1) compare the effects of a combined motor control and isolated lumbar extension exercise (MC+ILEX) versus a general exercise (GE) intervention on paraspinal muscle morphology, composition, and function, and (2) examine whether alterations in paraspinal muscle health were correlated with improvements in pain, function, and quality of life. Fifty participants with chronic LBP were randomly assigned to each group and underwent a 12-week supervised intervention program. Magnetic resonance imaging and ultrasound assessments were acquired at baseline, 6 and 12 weeks to examine the impact of each intervention on erector spinae (ES) and multifidus (MF) muscle size (cross-sectional area, CSA), composition, and function at L4-L5 and L5-S1. Self-reported questionnaires were also acquired to assess participant-oriented outcomes. Our findings indicated that the MC+ILEX group demonstrated greater improvements in MF and ES CSA, along with MF thickness at both levels (all p < 0.01). Both groups significantly improved in pain, function, and quality of life. This study provided preliminary results suggesting that an MC+ILEX intervention may improve paraspinal morphology while decreasing pain and disability.

Substrate oxidation during exercise in childhood acute lymphoblastic leukemia survivors

Children with acute lymphoblastic leukemia (ALL) are at high risk of developing long-term cardiometabolic complications during their survivorship. Maximal fat oxidation (MFO) is a marker during exercise of cardiometabolic health, and is associated with metabolic risk factors. Our aim was to characterize the carbohydrate and fat oxidation during exercise in childhood ALL survivors. Indirect calorimetry was measured in 250 childhood ALL survivors to quantify substrate oxidation rates during a cardiopulmonary exercise test. A best-fit third-order polynomial curve was computed for fat oxidation rate (mg/min) against exercise intensity (%V ̇ O2peak) and was used to determine the MFO and the peak fat oxidation (Fatmax). The crossover point was also identified. Differences between prognostic risk groups were assessed (ie, standard risk [SR], high risk with and without cardio-protective agent dexrazoxane [HR + DEX and HR]). MFO, Fatmax and crossover point were not different between the groups (p = .078; p = .765; p = .726). Fatmax and crossover point were achieved at low exercise intensities. A higher MFO was achieved by men in the SR group (287.8 ± 111.2 mg/min) compared to those in HR + DEX (239.8 ± 97.0 mg/min) and HR groups (229.3 ± 98.9 mg/min) (p = .04). Childhood ALL survivors have low fat oxidation during exercise and oxidize carbohydrates at low exercise intensities, independently of the cumulative doses of doxorubicin they received. These findings alert clinicians on the long-term impact of cancer treatments on childhood ALL survivors' substrate oxidation.

Crossover point and maximal fat oxidation training effects on blood lipid metabolism in young overweight women: a pilot study

Purpose: To determine the effects of weight reduction schemes using the exercise intensities corresponding to maximal fat oxidation (FATmax) and crossover point (COP). The effects of different intervention protocols on blood lipid metabolism were compared to explore how fat can be consumed and used more efficiently and provide a theoretical basis for weight loss through exercise. Methods: This study included 30 young overweight women randomly divided into the COP, FATmax, and control groups. Participants in the COP and FATmax groups exercised for 45 min four times a week for 8 weeks after the individual treadmill exercise test. The control group did not perform any exercise. Results: After 8 weeks of training, participants in the COP group significantly decreased weight (2.6 ± 3.3 kg), body mass index (0.91 ± 1.26 kg/m2), body fat percentage (1.21% ± 1.50%), and fat mass (1.90 ± 2.30 kg) (p < 0.05). They also had significantly decreased hip circumference (4.8 ± 3.3 cm), serum apolipoprotein B (ApoB) levels (15.48 ± 14.19 mg/dL), and ApoB/apolipoprotein AI (ApoAI) ratios (0.47 ± 0.37) (p < 0.01). However, their serum ApoAI levels were significantly increased (14.18 ± 10.24 mg/dL; p < 0.01). Participants in the FATmax group had significantly decreased hip circumference (2.4 ± 2.0 cm), serum ApoB levels (14.49 ± 11.00 mg/dL), and ApoB/ApoAI ratios (0.59 ± 0.30) (p < 0.01) but significantly increased serum ApoAI levels (29.53 ± 13.29 mg/dL; p < 0.01). No significant changes in physiological indexes were observed in participants in the control group. Conclusion: Personalised exercise intervention positively affected central obesity, effectively improving blood lipid metabolism and fat oxidation, reducing cardiovascular disease risk in young overweight women. COP training improved weight and body composition better than the FATmax exercise, while the latter provided greater improvements in serum ApoAI levels.

Pre-exercise meal on oxidation of energy substrates during maximal exercise test in non-trained individuals

Objective

This study aimed to compare the influence of a high carbohydrate meal versus high-fat meal on the oxidation of substrates during an exercise incremental test.

Materials and methods

Ten untrained male subjects underwent two days of the protocol. Randomly, they received a high carbohydrate meal or a high-fat meal, receiving the other one in the next protocol. On both days, they performed an incremental treadmill test, with heart rate and maximal oxygen consumption to estimate the oxidation of substrates.

Results

The high-fat meal showed an increase in the absolute amount of oxidized fat along with the incremental test (P < 0.05; effect size = 0.9528), and a reduction in the respiratory exchange ratio at low intensities (P < 0.05; effect size = 0.7765).

Conclusion

The meals presented no difference when compared to maximum oxidation point of substrates, the oxidation rate of substrates over time, and heart rate. A pre-test high-fat meal in untrained individuals was shown to be a modulating factor of total oxidized fats throughout the exercise, although it did not exert a significant effect on the rate of this oxidation over time.

Sex differences in body composition and serum metabolome responses to sustained, physical training suggest enhanced fat oxidation in women compared with men

Sex differences in energy metabolism during acute, submaximal exercise are well documented. Whether these sex differences influence metabolic and physiological responses to sustained, physically demanding activities is not well characterized. This study aimed to identify sex differences within changes in the serum metabolome in relation to changes in body composition, physical performance, and circulating markers of endocrine and metabolic status during a 17-day military training exercise. Blood was collected, and body composition and lower body power were measured before and after the training on 72 cadets (18 women). Total daily energy expenditure (TDEE) was assessed using doubly labeled water in a subset throughout. TDEE was greater in men (4,085 ± 482 kcal/d) than in women (2,982 ± 472 kcal/d, P < 0.001), but not after adjustment for dry lean mass (DLM). Men tended to lose more DLM than women (mean change [95% CI]: -0.2[-0.3, -0.1] vs. -0.0[-0.0, 0.0] kg, P = 0.063, Cohen's d = 0.50) and have greater reductions in lower body power (-244[-314, -174] vs. -130[-209, -51] W, P = 0.085, d = 0.49). Reductions in DLM and lower body power were correlated (r = 0.325, P = 0.006). Women demonstrated greater fat oxidation than men (Δfat mass/DLM: -0.20[-0.24, -0.17] vs. -0.15[-0.17, -0.13] kg, P = 0.012, d = 0.64). Metabolites within pathways of fatty acid, endocannabinoid, lysophospholipid, phosphatidylcholine, phosphatidylethanolamine, and plasmalogen metabolism increased in women relative to men. Independent of sex, changes in metabolites related to lipid metabolism were inversely associated with changes in body mass and positively associated with changes in endocrine and metabolic status. These data suggest that during sustained military training, women preferentially mobilize fat stores compared with men, which may be beneficial for mitigating loss of lean mass and lower body power.NEW & NOTEWORTHY Women preferentially mobilize fat stores compared with men in response to sustained, physically demanding military training, as evidenced by increased lipid metabolites and enhanced fat oxidation, which may be beneficial for mitigating loss of lean mass and lower body power.

The Metabolic Switch of Physical Activity in Non-Obese Insulin Resistant Individuals

Healthy non-obese insulin resistant (IR) individuals are at higher risk of metabolic syndrome. The metabolic signature of the increased risk was previously determined. Physical activity can lower the risk of insulin resistance, but the underlying metabolic pathways remain to be determined. In this study, the common and unique metabolic signatures of insulin sensitive (IS) and IR individuals in active and sedentary individuals were determined. Data from 305 young, aged 20-30, non-obese participants from Qatar biobank, were analyzed. The homeostatic model assessment of insulin resistance (HOMA-IR) and physical activity questionnaires were utilized to classify participants into four groups: Active Insulin Sensitive (ISA, n = 30), Active Insulin Resistant (IRA, n = 20), Sedentary Insulin Sensitive (ISS, n = 21) and Sedentary Insulin Resistant (SIR, n = 23). Differences in the levels of 1000 metabolites between insulin sensitive and insulin resistant individuals in both active and sedentary groups were compared using orthogonal partial least square discriminate analysis (OPLS-DA) and linear models. The study indicated significant differences in fatty acids between individuals with insulin sensitivity and insulin resistance who engaged in physical activity, including monohydroxy, dicarboxylate, medium and long chain, mono and polyunsaturated fatty acids. On the other hand, the sedentary group showed changes in carbohydrates, specifically glucose and pyruvate. Both groups exhibited alterations in 1-carboxyethylphenylalanine. The study revealed different metabolic signature in insulin resistant individuals depending on their physical activity status. Specifically, the active group showed changes in lipid metabolism, while the sedentary group showed alterations in glucose metabolism. These metabolic discrepancies demonstrate the beneficial impact of moderate physical activity on high risk insulin resistant healthy non-obese individuals by flipping their metabolic pathways from glucose based to fat based, ultimately leading to improved health outcomes. The results of this study carry significant implications for the prevention and treatment of metabolic syndrome in non-obese individuals.

The Effects of Exercise on Appetite-Regulating Hormone Concentrations over a 36-h Fast in Healthy Young Adults: A Randomized Crossover Study

Hunger and satiety are controlled by several physiological mechanisms, including pancreatic and gastrointestinal hormones. While the influence of exercise and fasting have been described individually, in relation to these hormones, there is a paucity of work showing the effects of the two modalities (fasting and exercise) combined. Twenty healthy adults (11 males, 9 females) completed both conditions of this study, each consisting of a 36-h water-only fast. One of the fasts began with treadmill exercise, and the differences between the conditions on various appetite hormones were measured every 12 h. The difference in the area under the curve between conditions for ghrelin was 211.8 ± 73.1 pg/mL (F = 8.40, p < 0.0105), and, for GLP-1, it was -1867.9 ± 850.4 pg/mL (F = 4.82, p < 0.0422). No significant differences were noted for areas under the curve between conditions for leptin, PP, PYY, insulin, or GIP. Initiating a fast with exercise lowers ghrelin concentrations and elevates GLP-1 concentrations. Given that ghrelin elicits feelings of hunger and GLP-1 signals feelings of satiety, adding exercise to the beginning of a fast may reduce some of the biological drive of hunger, which could make fasting more tolerable, leading to better adherence and more significant health outcomes.

Effects of 12-week combined training versus high intensity interval training on cardiorespiratory fitness, body composition and fat metabolism in obese male adults

Background

/Objectives: A weekly combination of a high volume of moderate-intensity continuous training (MICT) with a low volume of high-intensity interval training (HIIT) provides important improvements in body composition and physical capacities in individuals with obesity. However, previous studies did not determine the weekly proportions of HIIT and MICT a priori. This study aimed to investigate changes in body composition, physical capacities and the fat oxidation rate in obese male adults by comparing a combination of MICT and HIIT, called combined training (COMB), with HIIT for a 12-week period.

Methods

Thirty-four obese male adults (mean age: 39.4 ± 7.0 y; mean body mass index [BMI] 34.0 ± 4.2 kg m-2) participated in this study (n = 18 for COMB, n = 16 HIIT), attending ∼ 36 training sessions. The COMB group performed 3 repetitions of 2 min at 95% of peak oxygen uptake (V'O2 peak) (e.g., HIIT ≤20%), followed by 30 min at 60% of VO2 peak (e.g., MICT ≥80%). The HIIT group performed 5-7 repetitions of 2 min at 95% of VO2 peak. At baseline (PRE) and at the end of the training period (POST), body composition, VO2 peak, and the fat oxidation rate were measured. The two training programs were equivalent in caloric expenditure.

Results

At POST, body mass (BM) and fat mass (FM) decreased by a mean of 3.09 ± 3.21 kg and 3.90 ± 2.40 kg, respectively (P < 0.05), in both groups and V'O2 peak increased in both groups by a mean of 0.47 ± 0.34 L min-1 (P < 0.05). The maximal fat oxidation rate increased similarly in both groups from 0.32 ± 0.05 to 0.36 ± 0.06 g min-1 (P < 0.05).

Conclusion

COMB training represents a viable alternative to HIIT to improve anthropometric characteristics, physical capacities and fat oxidation in obese male adults.

Is fatty infiltration in paraspinal muscles reversible with exercise in people with low back pain? A systematic review

PURPOSE

Increased fatty infiltration in paraspinal muscles has been recognized as a feature of muscle quality loss in people with Low Back Pain (LBP) and is highly associated with the severity of LBP and dysfunction. Reducing fatty infiltration has been recognized as a rehabilitation aim. An earlier systematic review published in 2014 revealed conflicting evidence for the reversibility of paraspinal muscle quality by means of exercise and no updates have been published since. A new systematic literature search is warranted.

METHOD

Pubmed, CINAHL and Embase were searched from inception to July 2022. Randomized, non-randomized controlled trials (RCT and non-RCT) and single-arm trials were included if they reported the effect of exercise on paraspinal fatty infiltration in people with LBP. Effect sizes and statistical power were calculated for (1) exercise versus control, and (2) pre-post exercise changes. Available data from the RCTs were pooled via meta-analysis when appropriate. Otherwise, data were synthesized qualitatively.

RESULTS

Two RCTs, one non-RCT and three single-arm trials met the selection criteria. Data were not pooled due to substantial clinical heterogeneity. Effect sizes from the RCTs revealed no significant difference for exercise versus control. One single-arm trial with high risk of bias demonstrated a significant pre-post difference with moderate effect size, but only at one (T12-L1) of the investigated levels.

CONCLUSION

Moderate quality evidence is available that paraspinal fatty infiltration is not reversible with exercise in people with LBP. More larger RCT's are needed to draw firmer conclusions.

Intramuscular mitochondrial and lipid metabolic changes of rats after regular high-intensity interval training (HIIT) of different training periods

BACKGROUND

High-intensity Interval Training (HIIT) is a time-efficient form of exercise and has gained popularity in recent years. However, at molecular level, the understanding about the effects of HIIT is not comprehensive, and even less is elucidated about HIIT of different training duration cycles, although different durations always lead to different post-training consequences.

METHOD

In this study, by training SD rats using HIIT protocols lasting for different training duration cycles, we investigated the adaptive response of intramuscular triglyceride abundance as well as mitochondrial and lipid metabolic changes after HIIT training (2, 4, 6, 8, and 10 weeks). We selected 72 h after the last session of training as the time point of sacrifice.

RESULTS

The suppressed activation of the cAMP-PKA pathway indicates that skeletal muscle was in the recovery phase at this time point. Intramuscular triglyceride abundance was significantly elevated after 2, 4, and 10 weeks of HIIT. However, the lipid metabolism-related proteins inconsistently changed in a chaotic trend (see Table 1). The expression levels of PGC1-α and COX IV decreased after 2 and 4 weeks of training and raised after 6 and 8 weeks of training. The expression level of citrate synthase (CS) decreased after 2, 4, 8, and 10 weeks of training, and showed an upward trend after 6 weeks of training. While the activity of CS decreased after 2 and 8 weeks of training and showed an upward trend after 6 weeks of HIIT.

CONCLUSION

Given the abovementioned changing trends, we propose two speculations: (A) the damaged mitochondria oxidation capacity might be one of the causes of IMTG accumulation observed after 2 and 4 weeks of HIIT. This phase might be similar to the condition of type 2 diabetes. (B) after 6-week HIIT, mitochondria function and biogenesis might be improved and the IMTG contents declined to baseline. This might be explained as: mitochondrial enhancement increased the capacity of lipid oxidation and then offset the increase in IMTG achieved during the first 4 weeks. For HIIT Rat Modelling, if the aim is to observe HIIT-induced positive effects, caution should be exercised when considering 2 and 4 weeks of training under our HIIT frame. Also, implementing six-week training is at least effective for mitochondrial enhancement when using similar HIIT frame of this study.

Metabolomic Phenotypes Reflect Patient Sex and Injury Status: A Cross-Sectional Analysis of Human Synovial Fluid

Background

Post-traumatic osteoarthritis (PTOA) is caused by knee injuries like anterior cruciate ligament (ACL) injuries. Often, ACL injuries are accompanied by damage to other tissues and structures within the knee including the meniscus. Both are known to cause PTOA but underlying cellular mechanisms driving disease remain unknown. Aside from injury, patient sex is a prevalent risk factor associated with PTOA.

Hypothesis

Metabolic phenotypes of synovial fluid that differ by knee injury pathology and participant sex will be distinct from each other.

Study Design

A cross-sectional study.

Methods

Synovial fluid from n=33 knee arthroscopy patients between 18 and 70 years with no prior knee injuries was obtained pre-procedure and injury pathology assigned post-procedure. Synovial fluid was extracted and analyzed via liquid chromatography mass spectrometry metabolomic profiling to examine differences in metabolism between injury pathologies and participant sex. Additionally, samples were pooled and underwent fragmentation to identify metabolites.

Results

Metabolite profiles revealed that injury pathology phenotypes were distinct from each other where differences in endogenous repair pathways that are triggered post-injury were detected. Specifically, acute differences in metabolism mapped to amino acid metabolism, lipid-related oxidative metabolism, and inflammatory-associated pathways. Lastly, sexual dimorphic metabolic phenotypes were examined between male and female participants, and within injury pathology. Specifically, Cervonyl Carnitine and other identified metabolites differed in concentration between sexes.

Conclusions

The results of this study suggest that different injuries (e.g., ligament vs. meniscus), as well as sex are associated with distinct metabolic phenotypes. Considering these phenotypic associations, a greater understanding of metabolic mechanisms associated with specific injuries and PTOA development may yield data regarding how endogenous repair pathways differ between injury types. Furthermore, ongoing metabolomic analysis of synovial fluid in injured male and female patients can be performed to monitor PTOA development and progression.

Clinical Relevance

Extension of this work may potentially lead to the identification of biomarkers as well as drug targets that slow, stop, or reverse PTOA progression based on injury type and patient sex.

Durability is improved by both low and high intensity endurance training

Introduction: This is one of the first intervention studies to examine how low- (LIT) and high-intensity endurance training (HIT) affect durability, defined as 'time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise'. Methods: Sedentary and recreationally active men (n = 16) and women (n = 19) completed either LIT (average weekly training time 6.8 ± 0.7 h) or HIT (1.6 ± 0.2 h) cycling for 10 weeks. Durability was analyzed before and after the training period from three factors during 3-h cycling at 48% of pretraining maximal oxygen uptake (VO_2max): 1) by the magnitude and 2) onset of drifts (i.e. gradual change in energy expenditure, heart rate, rate of perceived exertion, ventilation, left ventricular ejection time, and stroke volume), 3) by the 'physiological strain', defined to be the absolute responses of heart rate and its variability, lactate, and rate of perceived exertion. Results: When all three factors were averaged the durability was improved similarly (time x group p = 0.42) in both groups (LIT: p = 0.03, g = 0.49; HIT: p = 0.01, g = 0.62). In the LIT group, magnitude of average of drifts and their onset did not reach statistically significance level of p < 0.05 (magnitude: 7.7 ± 6.8% vs. 6.3 ± 6.0%, p = 0.09, g = 0.27; onset: 106 ± 57 min vs. 131 ± 59 min, p = 0.08, g = 0.58), while averaged physiological strain improved (p = 0.01, g = 0.60). In HIT, both magnitude and onset decreased (magnitude: 8.8 ± 7.9% vs. 5.4 ± 6.7%, p = 0.03, g = 0.49; onset: 108 ± 54 min vs. 137 ± 57 min, p = 0.03, g = 0.61), and physiological strain improved (p = 0.005, g = 0.78). VO_2max increased only after HIT (time x group p < 0.001, g = 1.51). Conclusion: Durability improved similarly by both LIT and HIT based on reduced physiological drifts, their postponed onsets, and changes in physiological strain. Despite durability enhanced among untrained people, a 10-week intervention did not alter drifts and their onsets in a large amount, even though it attenuated physiological strain.

Metabolic responses to acute sprint interval exercise training performed after an oral 75-gram glucose load in individuals with overweight/obesity

There is evidence supporting that acute sprint interval training (SIT) might improve metabolic responses to postprandial glucose, but results are inconclusive. The aim of the present study was to explore the effects of acute SIT on metabolic response and substrate utilization in individuals with overweight/obesity after an oral 75-gram glucose challenge. Thirty-three participants with overweight/ obesity (32.7 ± 8.3 years, 24 male, 9 female) participated in the study and a crossover design was followed. After the 75-gram glucose load, participants were randomly allocated to two groups: no exercise (resting) or SIT protocol. Metabolic data including respiratory quotient (RQ) and substrate utilization rates (fats and carbohydrates) were collected using the COSMED Q-NRG + ® calorimeter. The RQ was significantly lower in the acute SIT group (0.76 [0.01]; p < 0.0001) than in the resting group (0.80 [0.01]; p = 0.036) at the 120-min postprandial time point, and the RQ area under the curve (AUC) was also lower in the SIT group (mean difference of -6.62, 95% CI -12.00 to -1.24; p = 0.0161). The contribution of fat to energy expenditure increased after SIT during the postprandial period whereas the contribution of carbohydrates decreased. The AUC for fat contribution was significantly higher (mean difference 2311.9, 95% confidence interval [CI] 578.8 to 4043.3; p = 0.0098) and the AUC for carbohydrate contribution was significantly lower (mean difference -2283.1, 95% CI -4040.2 to -527.1; p = 0.0117) in the SIT group than in the resting group. In conclusions, acute SIT might have a positive effect on metabolic responses to postprandial glucose and, accordingly, should be recommended for improving metabolism in people with overweight/obesity.