Beneficial metabolic adaptations due to endurance exercise training in the fasted state

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

Muscle fibre transition and transcriptional changes of horse skeletal muscles during traditional Mongolian endurance training

BACKGROUND

Traditional Mongolian endurance training is an effective way to improve the athletic ability of the horse for endurance events and is widely used. This incorporates aerobic exercise and intermittent fasting and these altered physiologic conditions are associated with switches between muscle fibre types.

OBJECTIVES

To better understand the adaption of horse skeletal muscle to traditional Mongolian endurance training from muscle fibre characteristics and transcriptional levels and to explore possible molecular mechanisms associated with the endurance performance of horses.

STUDY DESIGN

Before-after study.

METHODS

Muscle fibre type switches and muscle transcriptome changes in six Mongolian horses were assessed during 4 weeks of training. Transcriptomic and histochemical analyses were performed. The activities of oxidative and glycolytic metabolic enzymes were analysed and we generated deep RNA-sequencing data relating to skeletal muscles.

RESULTS

A fast-to-slow muscle fibre transition occurred in horse skeletal muscles, with a concomitant increase of oxidative enzyme activity and decreased glycolytic enzyme activity. Numerous differentially expressed genes were involved in the control of muscle protein balance and degradation. Differential alternative splicing events were also found during training which included exon-skipping events in Ttn that were associated with muscle atrophy. Differentially expressed noncoding RNAs showed connections with muscle protein balance-related pathways and fibre type specification via the post-transcriptional regulation of miRNA.

MAIN LIMITATIONS

The study focuses on horse athletic ability only from the aspect of muscular adaptation.

CONCLUSION

Traditional Mongolian endurance training-induced muscle fibre transition and metabolic and transcriptional changes. Muscle-specific non-coding RNAs could contribute to these transcriptomic changes during training.

The effect of pre-exercise protein intake on substrate metabolism, energy expenditure, and energy intake: a dose-response study

BACKGROUND

Pre-exercise protein consumption does not seem to influence substrate metabolism during exercise compared to fasted exercise, however it is unclear if the protein dose impacts on this effect.

METHODS

In a randomized, double-blinded within-subject design trial, healthy, active males and females (n = 15, 25 ± 5 yrs, O2peak: 47.5 ± 8.8 ml/kg/min) completed 1 h of cycling exercise at 60% peak power output 30 min after having consumed either 0, 20, or 40 g of whey protein. Indirect calorimetry was used to measure substrate oxidation during exercise and baseline and post-exercise resting energy expenditure. Blood samples were taken throughout the trials to measure metabolic responses. Free-living food intake post-trial was collected using food diaries.

RESULTS

Fat oxidation rates during exercise did not differ between the three conditions (p = 0.19) with small effect sizes between conditions (Cohen's dz: 0 vs. 20 g = 0.22, 0 vs. 40 g = 0.47, 20 vs. 40 g = 0.27). Serum insulin was higher in the protein groups vs. 0 g (p < 0.05), whereas non-esterified fatty acids were higher in the 0 g compared to 20 and 40 g (p < 0.05). Glucose was significantly lower after 15 min of exercise in 20 and 40 g vs. 0 g (p = 0.01). Resting energy expenditure was elevated post-exercise (p < 0.001), without an interaction for protein dose (p = 0.90). Post-trial free-living energy intake was not different between conditions (p = 0.31), but 24-h energy intake was significantly higher in 40 vs. 0 g (p = 0.04).

CONCLUSION

Protein doses up to 40 g do not seem to impair fat oxidation rates during exercise compared to fasted exercise and could be considered as a nutritional strategy for exercising individuals who struggle to include fasted exercise in their training.

Dietary Intake of Protein and Essential Amino Acids for Sustainable Muscle Development in Elite Male Athletes

Athletes need to develop a relatively high muscle mass and low body adipose tissue for the sake of better athletic performance. A full range of nine essential amino acids and eleven non-essential amino acids have to attend in appropriate amounts for protein biosynthesis. The aim of the observational comparative cross-sectional study was to assess the association between the diet quality profile and training-induced muscle mass estimated by bioelectrical impedance among elite male athletes. The research sample comprised 18.1 ± 3.1 year-old Lithuanian professional male athletes (n = 234). The study participants were enrolled to complete 24-h dietary recalls of three non-consecutive days. The body composition was assessed using the bioelectrical impedance analysis (BIA) method. The present study showed a significant insufficiency of the mean carbohydrate intake of 5.7 g/kg/day in a group of aerobic male athletes. The lower muscle mass of aerobic male athletes was related to the lower-carbohydrate diet (adjusted odd ratio (ORadj) 0.3; 95% confidence interval (CI): 0.1-0.7). The mean protein intake of 1.8 g/kg/day was optimal for anabolism in the samples of both anaerobic and aerobic male athletes. The protein intake in appropriate doses was potentially associated with an increase in muscle mass only in anaerobic male athletes (ORadj 2.2; 95% CI: 1.3-3.7). The positive relationship was revealed between the possible muscle mass gain and the increased intakes of amino acids such as isoleucine and histidine among anaerobic athletes (ORadj 2.9; 95% CI: 1.1-4.7 and ORadj 2.9; 95% CI: 1.0-4.3, respectively). An inverse feasible association was indicated between a higher intake of valine and lower muscle mass quantities among anaerobic male athletes (ORadj 0.1; 95% CI: 0.1-0.5). The recommendations for sports nutritionists should emphasize the necessity of advising professional athletes on dietary strategies on how to manipulate dietary amino acid composition with respect to achieving long-term body composition goals.

Nutritional Strategies for Endurance Cyclists - Periodized Nutrition, Ketogenic Diets, and Other Considerations

ABSTRACT

Cycling is a growing sport worldwide since the COVID-19 pandemic. With the growing availability and interest in long distance events, professional and amateur cyclists are pushing themselves further and harder than ever before. Training and nutrition should be understood by the sports medicine professional in order to guide counseling toward proper fueling to avoid health consequences. This article reviews macronutrients and micronutrients, periodized training and nutrition, and the relevance of the ketogenic diet for endurance cyclists riding greater than 90 min.

Intermittent Fasting and Physical Exercise for Preventing Metabolic Disorders through Interaction with Gut Microbiota: A Review

Metabolic disorders entail both health risks and economic burdens to our society. A considerable part of the cause of metabolic disorders is mediated by the gut microbiota. The gut microbial structure and function are susceptible to dietary patterns and host physiological activities. A sedentary lifestyle accompanied by unhealthy eating habits propels the release of harmful metabolites, which impair the intestinal barrier, thereby triggering a constant change in the immune system and biochemical signals. Noteworthy, healthy dietary interventions, such as intermittent fasting, coupled with regular physical exercise can improve several metabolic and inflammatory parameters, resulting in stronger beneficial actions for metabolic health. In this review, the current progress on how gut microbiota may link to the mechanistic basis of common metabolic disorders was discussed. We also highlight the independent and synergistic effects of fasting and exercise interventions on metabolic health and provide perspectives for preventing metabolic disorders.

A genome-wide landscape of mRNAs, miRNAs, lncRNAs, and circRNAs of skeletal muscles during dietary restriction in Mongolian horses

The proportion of different muscle fibers is essential for the horse breed's aptitude for athletic activities. Adaptation of locomotor muscle is correlated with altered physiologic conditions. To investigate the adaptive changes of muscle fiber phenotype and transcriptome in horse skeletal muscle during dietary restriction (DR). The muscle fiber type distribution and deep RNA-seq analysis of detecting differentially expressed mRNAs (DEGs), miRNA (DEMIRs), lncRNAs (DELs), circRNAs (DECs), and their function analysis were investigated in gluteus medius muscle of Mongolian horses during DR. A total of 1433 DEGs, 5 DEMIRs, 329 DELs, and 53 DECs were identified. Differing from non-uniform muscle fiber type changing, functional enrichment analysis showed that most downregulated DEGs were associated in muscle contraction, fuel energy metabolism, and protein balance. Linkages between non-coding RNA and mRNA landscape were detected from their functional changes. Our study provides new insights into the expressional changes of mRNA and non-coding RNA in horse skeletal muscles during DR, which might improve our understanding of the molecular mechanisms regulating muscle adaption during DR for racing horses.

Fasted Sprint Interval Training Results in Some Beneficial Skeletal Muscle Metabolic, but Similar Metabolomic and Performance Adaptations Compared With Carbohydrate-Fed Training in Recreationally Active Male

Endurance training in fasted conditions (FAST) induces favorable skeletal muscle metabolic adaptations compared with carbohydrate feeding (CHO), manifesting in improved exercise performance over time. Sprint interval training (SIT) is a potent metabolic stimulus, however nutritional strategies to optimize adaptations to SIT are poorly characterized. Here we investigated the efficacy of FAST versus CHO SIT (4-6 × 30-s Wingate sprints interspersed with 4-min rest) on muscle metabolic, serum metabolome and exercise performance adaptations in a double-blind parallel group design in recreationally active males. Following acute SIT, we observed exercise-induced increases in pan-acetylation and several genes associated with mitochondrial biogenesis, fatty acid oxidation, and NAD+-biosynthesis, along with favorable regulation of PDK4 (p = .004), NAMPT (p = .0013), and NNMT (p = .001) in FAST. Following 3 weeks of SIT, NRF2 (p = .029) was favorably regulated in FAST, with augmented pan-acetylation in CHO but not FAST (p = .033). SIT induced increases in maximal citrate synthase activity were evident with no effect of nutrition, while 3-hydroxyacyl-CoA dehydrogenase activity did not change. Despite no difference in the overall serum metabolome, training-induced changes in C3:1 (p = .013) and C4:1 (p = .010) which increased in FAST, and C16:1 (p = .046) and glutamine (p = .021) which increased in CHO, were different between groups. Training-induced increases in anaerobic (p = .898) and aerobic power (p = .249) were not influenced by nutrition. These findings suggest some beneficial muscle metabolic adaptations are evident in FAST versus CHO SIT following acute exercise and 3 weeks of SIT. However, this stimulus did not manifest in differential exercise performance adaptations.

Intramuscular lipid utilization during exercise: a systematic review, meta-analysis, and meta-regression

Intramuscular lipid (IMCL) utilization during exercise was controversial as numerous studies did not observe a decline in IMCL content post-exercise when assessed in muscle biopsies using biochemical techniques. Contemporary techniques including immunofluorescence microscopy and ¹H-magnetic resonance spectroscopy (¹H-MRS) offer advantages over biochemical techniques. The primary aim of this systematic review, meta-analysis, and meta-regression was to examine the net degradation of IMCL in response to an acute bout of cycling exercise in humans, as assessed with different analytical approaches. A secondary aim was to explore the factors influencing IMCL degradation including feeding status, exercise variables, and participant characteristics. A total of 44 studies met the inclusion criteria using biochemical, immunofluorescence, and ¹H-MRS techniques. A meta-analysis was completed using a random effects model and percentage change in IMCL content calculated from the standardized mean difference. Cycling exercise resulted in a net degradation of IMCL regardless of technique (total effect -23.7%, 95% CI = -28.7 to -18.7%) and there was no difference when comparing fasted versus fed-state exercise (P > 0.05). IMCL degradation using immunofluorescence techniques detected larger effects in type I fibers compared with whole muscle using biochemical techniques (P = 0.003) and in type I fibers compared with type II fibers (P < 0.001). Although IMCL degradation was associated with exercise duration, V̇o_2max, and BMI, none of these factors independently related to the change in IMCL content. These findings provide strong evidence that the analytical approach can influence the assessment of IMCL degradation in human skeletal muscle in response to exercise.

Exercise Timing Matters for Glycogen Metabolism and Accumulated Fat Oxidation over 24 h

Due to increasingly diverse lifestyles, exercise timings vary between individuals: before breakfast, in the afternoon, or in the evening. The endocrine and autonomic nervous systems, which are associated with metabolic responses to exercise, show diurnal variations. Moreover, physiological responses to exercise differ depending on the timing of the exercise. The postabsorptive state is associated with greater fat oxidation during exercise compared to the postprandial state. The increase in energy expenditure persists during the post-exercise period, known as "Excess Post-exercise Oxygen Consumption". A 24 h evaluation of accumulated energy expenditure and substrate oxidation is required to discuss the role of exercise in weight control. Using a whole-room indirect calorimeter, researchers revealed that exercise performed during the postabsorptive state, but not during the postprandial state, increased accumulated fat oxidation over 24 h. The time course of the carbohydrate pool, as estimated by indirect calorimetry, suggests that glycogen depletion after postabsorptive exercise underlies an increase in accumulated fat oxidation over 24 h. Subsequent studies using ¹³C magnetic resonance spectroscopy confirmed that the variations in muscle and liver glycogen caused by postabsorptive or postprandial exercise were consistent with indirect calorimetry data. These findings suggest that postabsorptive exercise alone effectively increases 24 h fat oxidation.

Acute effects of a single moderate-intensity exercise bout performed in fast or fed states on cell metabolism and signaling: Comparison between lean and obese rats

AIMS

Although the benefits of exercise can be potentiated by fasting in healthy subjects, few studies evaluated the effects of this intervention on the metabolism of obese subjects. This study investigated the immediate effects of a single moderate-intensity exercise bout performed in fast or fed states on the metabolism of gastrocnemius and soleus of lean and obese rats.

MAIN METHODS

Male rats received a high-fat diet (HFD) for twelve weeks to induce obesity or were fed standard diet (SD). After this period, the animals were subdivided in groups: fed and rest (FER), fed and exercise (30 min treadmill, FEE), 8 h fasted and rest (FAR) and fasted and exercise (FAE). Muscle samples were used to investigate the oxidative capacity and gene expression of AMPK, PGC1α, SIRT1, HSF1 and HSP70.

KEY FINDINGS

In relation to lean animals, obese animals' gastrocnemius glycogen decreased 60 %, triglycerides increased 31 %; glucose and alanine oxidation decreased 26 % and 38 %, respectively; in soleus, triglycerides reduced 46 % and glucose oxidation decreased 37 %. Exercise and fasting induced different effects in glycolytic and oxidative muscles of obese rats. In soleus, fasting exercise spared glycogen and increased palmitate oxidation, while in gastrocnemius, glucose oxidation increased. In obese animals' gastrocnemius, AMPK expression decreased 29 % and SIRT1 increased 28 % in relation to lean. The AMPK response was more sensitive to exercise and fasting in lean than obese rats.

SIGNIFICANCE

Exercise and fasting induced different effects on the metabolism of glycolytic and oxidative muscles of obese rats that can promote health benefits in these animals.

From evidence to implementation of lifestyle behaviour in cancer prevention and control: A Preventive Medicine Golden Jubilee Commentary

Preventive interventions targeting tobacco, alcohol, healthy diets and physical activity are key strategies to tackle the most pressing health challenges in modern society. A major gap remains in how to translate research evidence into population-level behaviour change to reduce the disease burden. We use the case for the role of physical activity-related behaviour and cancer to illustrate the iterative, multidirectional, and transdisciplinary nature of translational research. The issues we address in this context are generalizable and applicable to other behavioral risk factors and non-communicable diseases. There is now solid evidence that physical activity reduces cancer risk and improves outcomes after cancer diagnosis. Here we provide a framework for how to implement this knowledge into real-world settings. We provide the rationale for combining systems, causal and design thinking to develop interventions that can be implemented for this type of behaviour change. The proposed model is iterative, multidirectional and transdisciplinary. We identify major knowledge gaps in epidemiology and science of behaviour change on physical activity and cancer control and propose approaches to suggest priorities for future research.

Periodised Carbohydrate Intake Does Not Affect Substrate Oxidation but May Contribute to Endurance Capacity

The aim of this study was to investigate whether periodising carbohydrate intake around specific training sessions will enhance endurance training adaptations.Seventeen healthy recreationally endurance-trained males (n = 5) and females (n = 12) (27.5 ± 5.4 years) participated in a four-week training intervention. Participants were divided into two groups: FASTED (stayed fasted between evening high-intensity interval training session and low-intensity training session in the following morning) and FED (no restriction in food intake). Pre- and post-testing included peak oxygen uptake (VO_2peak), anaerobic capacity, and 60 min submaximal running tests. Fasted venous blood samples were drawn for the determination of triglyceride and glucose concentrations.VO_2peak increased in both FASTED (4.4 ± 3.0%, p = 0.001) and FED (4.6 ± 4.2%, p = 0.017), whereas maximal running velocity increased only in the FASTED (3.5 ± 2.7%, p = 0.002). Lactate concentrations in the anaerobic test after intervention were greater in FASTED than FED (p = 0.025-0.041). Running time in the anaerobic test was improved in FASTED (from 64.1 ± 15.6-86.3 ± 23.2 s, p < 0.001) but not in FED (from 56.4 ± 15.2-66.9 ± 21.3 s, p = 0.099). Substrate oxidation did not change after intervention in either of the groups (p = 0.052-0.597). Heart rate was lower in the submaximal running test in FASTED (p < 0.001) but not in FED (p = 0.097).Training with periodised carbohydrate availability does not have any effect on substrate oxidation. However, it seems to enhance the capacity to perform high-intensity exercise.

Loss of hepatic phosphoenolpyruvate carboxykinase 1 dysregulates metabolic responses to acute exercise but enhances adaptations to exercise training in mice

Acute exercise increases liver gluconeogenesis to supply glucose to working muscles. Concurrently, elevated liver lipid breakdown fuels the high energetic cost of gluconeogenesis. This functional coupling between liver gluconeogenesis and lipid oxidation has been proposed to underlie the ability of regular exercise to enhance liver mitochondrial oxidative metabolism and decrease liver steatosis in individuals with nonalcoholic fatty liver disease. Herein we tested whether repeated bouts of increased hepatic gluconeogenesis are necessary for exercise training to lower liver lipids. Experiments used diet-induced obese mice lacking hepatic phosphoenolpyruvate carboxykinase 1 (KO) to inhibit gluconeogenesis and wild-type (WT) littermates. 2H/13C metabolic flux analysis quantified glucose and mitochondrial oxidative fluxes in untrained mice at rest and during acute exercise. Circulating and tissue metabolite levels were determined during sedentary conditions, acute exercise, and refeeding postexercise. Mice also underwent 6 wk of treadmill running protocols to define hepatic and extrahepatic adaptations to exercise training. Untrained KO mice were unable to maintain euglycemia during acute exercise resulting from an inability to increase gluconeogenesis. Liver triacylglycerides were elevated after acute exercise and circulating β-hydroxybutyrate was higher during postexercise refeeding in untrained KO mice. In contrast, exercise training prevented liver triacylglyceride accumulation in KO mice. This was accompanied by pronounced increases in indices of skeletal muscle mitochondrial oxidative metabolism in KO mice. Together, these results show that hepatic gluconeogenesis is dispensable for exercise training to reduce liver lipids. This may be due to responses in ketone body metabolism and/or metabolic adaptations in skeletal muscle to exercise.NEW & NOTEWORTHY Exercise training reduces hepatic steatosis partly through enhanced hepatic terminal oxidation. During acute exercise, hepatic gluconeogenesis is elevated to match the heightened rate of muscle glucose uptake and maintain glucose homeostasis. It has been postulated that the hepatic energetic stress induced by elevating gluconeogenesis during acute exercise is a key stimulus underlying the beneficial metabolic responses to exercise training. This study shows that hepatic gluconeogenesis is not necessary for exercise training to lower liver lipids.

Effect of Time-Restricted Feeding on Anthropometric, Metabolic, and Fitness Parameters: A Systematic Review

Time restricted feeding (TRF) as a form of intermittent fasting (IF) has gained popularity because its ability to reduce body mass (BM) without an emphasis on caloric restriction. However, how this dietary protocol may affect health, fitness, and performance in a relatively healthy cohort remains less clear. The purpose of this article was to systematically review the current literature concerning the effect of TRF on anthropometric, metabolic, and fitness parameters in normal-weight adults and overweight and obese individuals. A systematic search of English literature was conducted through databases including PubMed, CINAHL, and Google Scholar. The search was facilitated by using various combinations of key words related to nutritional interventions, i.e., IF and TRF, and outcomes of interest, i.e., BM, body composition, glucose, insulin, lipid, fitness, and performance. The article selection was made based on the inclusion and exclusion criteria concerning the participants' characteristics, study design, intervention protocols, and targeted dependent variables. Twenty-three full-text longitudinal randomized and nonrandomized controlled studies were selected for this review. Our analysis indicates that TRF can reduce BM and improve nutrient metabolism in both normal- and over-weight individuals. TRF does not appear to alter protein synthesis and fat-free mass nor hamper aerobic fitness and muscular performance among physically active individuals including athletes. In conclusion, TRF as a more easily adaptable form of IF is a promising dietary approach to improving body composition and metabolic health while maintaining fitness and muscular function. However, more research is needed before this dietary protocol can be fully recommended for athletes especially those competing in sports that demand strength and power.Key teaching points and nutritional relevanceTime-restricted feeding (TRF) differs from other fasting protocols due to its emphasis on restricting eating window rather than caloric intake and can be more easily adopted by simply skipping a meal.Its deemphasis on caloric restriction appeals to many young and physically active individuals wanting to optimize body composition but needing sufficient energy to support their physical training and daily activity.Much of what is known regarding the impact of TRF on fitness and athletic performance was derived from studies that use the Ramadan fasting protocol, which differs from TRF in terms of protocol duration and feeding schedule.This review concludes that TRF is a promising dietary approach to improving body composition and metabolic health while maintaining fitness and muscular function in both normal- and over-weight individuals.Due to limited evidence concerning TRF and athletic performance, more research is needed before this dietary protocol can be fully recommended for athletes especially those competing in sports that demand strength and power.

High intramuscular triglyceride turnover rates and the link to insulin sensitivity: influence of obesity, type 2 diabetes and physical activity

Large intramuscular triglyceride (IMTG) stores in sedentary, obese individuals have been linked to insulin resistance, yet well-trained athletes exhibit high IMTG levels whilst maintaining insulin sensitivity. Contrary to previous assumptions, it is now known that IMTG content per se does not result in insulin resistance. Rather, insulin resistance is caused, at least in part, by the presence of high concentrations of harmful lipid metabolites, such as diacylglycerols and ceramides in muscle. Several mechanistic differences between obese sedentary individuals and their highly trained counterparts have been identified, which determine the differential capacity for IMTG synthesis and breakdown in these populations. In this review, we first describe the most up-to-date mechanisms by which a low IMTG turnover rate (both breakdown and synthesis) leads to the accumulation of lipid metabolites and results in skeletal muscle insulin resistance. We then explore current and potential exercise and nutritional strategies that target IMTG turnover in sedentary obese individuals, to improve insulin sensitivity. Overall, improving IMTG turnover should be an important component of successful interventions that aim to prevent the development of insulin resistance in the ever-expanding sedentary, overweight and obese populations. Novelty: A description of the most up-to-date mechanisms regulating turnover of the IMTG pool. An exploration of current and potential exercise/nutritional strategies to target and enhance IMTG turnover in obese individuals. Overall, highlights the importance of improving IMTG turnover to prevent the development of insulin resistance.

The acute effect of fasted exercise on energy intake, energy expenditure, subjective hunger and gastrointestinal hormone release compared to fed exercise in healthy individuals: a systematic review and network meta-analysis

OBJECTIVE

To determine the acute effect of fasted and fed exercise on energy intake, energy expenditure, subjective hunger and gastrointestinal hormone release.

METHODS

CENTRAL, Embase, MEDLINE, PsycInfo, PubMed, Scopus and Web of Science databases were searched to identify randomised, crossover studies in healthy individuals that compared the following interventions: (i) fasted exercise with a standardised post-exercise meal [FastEx + Meal], (ii) fasted exercise without a standardised post-exercise meal [FastEx + NoMeal], (iii) fed exercise with a standardised post-exercise meal [FedEx + Meal], (iv) fed exercise without a standardised post-exercise meal [FedEx + NoMeal]. Studies must have measured ad libitum meal energy intake, within-lab energy intake, 24-h energy intake, energy expenditure, subjective hunger, acyl-ghrelin, peptide YY, and/or glucagon-like peptide 1. Random-effect network meta-analyses were performed for outcomes containing ≥5 studies.

RESULTS

17 published articles (23 studies) were identified. Ad libitum meal energy intake was significantly lower during FedEx + Meal compared to FedEx + NoMeal (MD: -489 kJ; 95% CI, -898 to -80 kJ; P = 0.019). Within-lab energy intake was significantly lower during FastEx + NoMeal compared to FedEx + NoMeal (MD: -1326 kJ; 95% CI, -2102 to -550 kJ; P = 0.001). Similarly, 24-h energy intake following FastEx + NoMeal was significantly lower than FedEx + NoMeal (MD: -2095 kJ; 95% CI, -3910 kJ to -280 kJ; P = 0.024). Energy expenditure was however significantly lower during FastEx + NoMeal compared to FedEx+NoMeal (MD: -0.67 kJ/min; 95% CI, -1.10 to -0.23 kJ/min; P = 0.003). Subjective hunger was significantly higher during FastEx + Meal (MD: 13 mm; 95% CI, 5-21 mm; P = 0.001) and FastEx + NoMeal (MD: 23 mm; 95% CI, 16-30 mm; P < 0.001) compared to FedEx + NoMeal.

CONCLUSION

FastEx + NoMeal appears to be the most effective strategy to produce a short-term decrease in energy intake, but also results in increased hunger and lowered energy expenditure. Concerns regarding experimental design however lower the confidence in these findings, necessitating future research to rectify these issues when investigating exercise meal timing and energy balance.

PROSPERO REGISTRATION NUMBER

CRD42020208041.

KEY POINTS

Fed exercise with a standardised post-exercise meal resulted in the lowest energy intake at the ad libitum meal served following exercise completion. Fasted exercise without a standardised post-exercise meal resulted in the lowest within-lab and 24-h energy intake, but also produced the lowest energy expenditure and highest hunger. Methodological issues lower the confidence in these findings and necessitate future work to address identified problems.

Acute Succinate Administration Increases Oxidative Phosphorylation and Skeletal Muscle Explosive Strength via SUCNR1

Endurance training and explosive strength training, with different contraction protein and energy metabolism adaptation in skeletal muscle, are both beneficial for physical function and quality of life. Our previous study found that chronic succinate feeding enhanced the endurance exercise of mice by inducing skeletal muscle fiber-type transformation. The purpose of this study is to investigate the effect of acute succinate administration on skeletal muscle explosive strength and its potential mechanism. Succinate was injected to mature mice to explore the acute effect of succinate on skeletal muscle explosive strength. And C2C12 cells were used to verify the short-term effect of succinate on oxidative phosphorylation. Then the cells interfered with succinate receptor 1 (SUCNR1) siRNA, and the SUCNR1-GKO mouse model was used for verifying the role of SUCNR1 in succinate-induced muscle metabolism and expression and explosive strength. The results showed that acute injection of succinate remarkably improved the explosive strength in mice and also decreased the ratio of nicotinamide adenine dinucleotide (NADH) to NAD⁺ and increased the mitochondrial complex enzyme activity and creatine kinase (CK) activity in skeletal muscle tissue. Similarly, treatment of C2C12 cells with succinate revealed that succinate significantly enhanced oxidative phosphorylation with increased adenosine triphosphate (ATP) content, CK, and the activities of mitochondrial complex I and complex II, but with decreased lactate content, reactive oxygen species (ROS) content, and NADH/NAD⁺ ratio. Moreover, the succinate's effects on oxidative phosphorylation were blocked in SUCNR1-KD cells and SUCNR1-KO mice. In addition, succinate-induced explosive strength was also abolished by SUCNR1 knockout. All the results indicate that acute succinate administration increases oxidative phosphorylation and skeletal muscle explosive strength in a SUCNR1-dependent manner.

Factors Influencing AMPK Activation During Cycling Exercise: A Pooled Analysis and Meta-Regression

BACKGROUND

The 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cellular energy sensor that is activated by increases in the cellular AMP/adenosine diphosphate:adenosine triphosphate (ADP:ATP) ratios and plays a key role in metabolic adaptations to endurance training. The degree of AMPK activation during exercise can be influenced by many factors that impact on cellular energetics, including exercise intensity, exercise duration, muscle glycogen, fitness level, and nutrient availability. However, the relative importance of these factors for inducing AMPK activation remains unclear, and robust relationships between exercise-related variables and indices of AMPK activation have not been established.

OBJECTIVES

The purpose of this analysis was to (1) investigate correlations between factors influencing AMPK activation and the magnitude of change in AMPK activity during cycling exercise, (2) investigate correlations between commonly reported measures of AMPK activation (AMPK-α2 activity, phosphorylated (p)-AMPK, and p-acetyl coenzyme A carboxylase (p-ACC), and (3) formulate linear regression models to determine the most important factors for AMPK activation during exercise.

METHODS

Data were pooled from 89 studies, including 982 participants (93.8% male, maximal oxygen consumption [[Formula: see text]] 51.9 ± 7.8 mL kg^-1 min^-1). Pearson's correlation analysis was performed to determine relationships between effect sizes for each of the primary outcome markers (AMPK-α2 activity, p-AMPK, p-ACC) and factors purported to influence AMPK signaling (muscle glycogen, carbohydrate ingestion, exercise duration and intensity, fitness level, and muscle metabolites). General linear mixed-effect models were used to examine which factors influenced AMPK activation.

RESULTS

Significant correlations (r = 0.19-0.55, p < .05) with AMPK activity were found between end-exercise muscle glycogen, exercise intensity, and muscle metabolites phosphocreatine, creatine, and free ADP. All markers of AMPK activation were significantly correlated, with the strongest relationship between AMPK-α2 activity and p-AMPK (r = 0.56, p < 0.001). The most important predictors of AMPK activation were the muscle metabolites and exercise intensity.

CONCLUSION

Muscle glycogen, fitness level, exercise intensity, and exercise duration each influence AMPK activity during exercise when all other factors are held constant. However, disrupting cellular energy charge is the most influential factor for AMPK activation during endurance exercise.

Divergent serum metabolomic, skeletal muscle signaling, transcriptomic, and performance adaptations to fasted versus whey protein-fed sprint interval training

Sprint interval training (SIT) is a time-efficient alternative to endurance exercise, conferring beneficial skeletal muscle metabolic adaptations. Current literature has investigated the nutritional regulation of acute and chronic exercise-induced metabolic adaptations in muscle following endurance exercise, principally comparing the impact of training in fasted and carbohydrate-fed (CHO) conditions. Alternative strategies such as exercising in low CHO, protein-fed conditions remain poorly characterized, specifically pertaining to adaptations associated with SIT. Thus, this study aimed to compare the metabolic and performance adaptations to acute and short-term SIT in the fasted state with preexercise hydrolyzed (WPH) or concentrated (WPC) whey protein supplementation. In healthy males, preexercise protein ingestion did not alter exercise-induced increases in PGC-1α, PDK4, SIRT1, and PPAR-δ mRNA expression following acute SIT. However, supplementation of WPH beneficially altered acute exercise-induced CD36 mRNA expression. Preexercise protein ingestion attenuated acute exercise-induced increases in muscle pan-acetylation and PARP1 protein content compared with fasted SIT. Acute serum metabolomic differences confirmed greater preexercise amino acid delivery in protein-fed compared with fasted conditions. Following 3 wk of SIT, training-induced increases in mitochondrial enzymatic activity and exercise performance were similar across nutritional groups. Interestingly, resting muscle acetylation status was downregulated in WPH conditions following training. Such findings suggest preexercise WPC and WPH ingestion positively influences metabolic adaptations to SIT compared with fasted training, resulting in either similar or enhanced performance adaptations. Future studies investigating nutritional modulation of metabolic adaptations to exercise are warranted to build upon these novel findings.NEW & NOTEWORTHY These are the first data to show the influence of preexercise protein on serum and skeletal muscle metabolic adaptations to acute and short-term sprint interval training (SIT). Preexercise whey protein concentrate (WPC) or hydrolysate (WPH) feeding acutely affected the serum metabolome, which differentially influenced acute and chronic changes in mitochondrial gene expression, intracellular signaling (acetylation and PARylation) resulting in either similar or enhanced performance outcomes when compared with fasted training.

Diurnal variations in muscle and liver glycogen differ depending on the timing of exercise

It has been suggested that glycogen functions not only in carbohydrate energy storage, but also as molecular sensors capable of activating lipolysis. This study aimed to compare the variation in liver and muscle glycogen during the day due to different timing of exercise. Nine healthy young men participated in two trials in which they performed a single bout of exercise at 70% of their individual maximal oxygen uptake for 60 min in the post-absorptive (morning) or post-prandial (afternoon) state. Liver and muscles glycogen levels were measured using carbon magnetic resonance spectroscopy (13C MRS). Diurnal variations in liver and muscle glycogen compared to baseline levels were significantly different depending on the timing of exercise. The effect of the timing of exercise on glycogen fluctuation is known to be related to a variety of metabolic signals, and the results of this study will be useful for future research on energy metabolism.

Use of real-time cadence to prescribe aerobic physical activity intensity and its comparison with existing methods

The purpose of this study was to determine the effectiveness of physical activity intensity prescription using real-time cadence on achieving the required intensities for health benefits. Forty adults (18-65 years) participated in the study. The intensity prescriptions included Rating of Perceived Exertion, Talk Test, Heart Rate, and Real-Time Cadence. The participants performed a2-min trial for both moderate- and vigorous-intensity according to each prescription. Atri-axial accelerometer was used as acriterion measure. After completion of the trials, participant's preference for the prescriptions was assessed by three domains (e.g., understanding, performing, maintaining). The compliance and achievement rates of RC were calculated and compared to other prescription methods. Coefficient of Variance was used to evaluate the extent of variation of intensity during the trials. Higher compliance rates were found in both moderate- (92.1%) and vigorous-intensity (94.9%) when using RC. When using RC, most participants (92.5%) were able to achieve the targeted moderate-intensity, but not for vigorous-intensity although asignificant difference was found between the two intensities (p < .001). Overall, RC was the most favoured method in all three domains. RC is apromising tool to prescribe moderate-intensity of physical activity for health benefits but still needs to be refined on prescribing vigorous-intensity.

Four Weeks of 16/8 Time Restrictive Feeding in Endurance Trained Male Runners Decreases Fat Mass, without Affecting Exercise Performance

Background: Time restricted Feeding (TRF) is a dietary pattern utilized by endurance athletes, but there is insufficient data regarding its effects on performance and metabolism in this population. The purpose of this investigation was to examine the effects of a 16/8 TRF dietary pattern on exercise performance in trained male endurance runners. Methods: A 4-week randomized crossover intervention was used to compare an 8-h TRF to a 12-h normal diet (ND) feeding window. Exercise training and dietary intake were similar across interventions. Runners completed a dual-energy X-ray absorptiometry (DXA) scan to assess body composition, a graded treadmill running test to assess substrate utilization, and ran a 10 km time trial to assess performance. Results: There was a significant decrease in fat mass in the TRF intervention (−0.8 ± 1.3 kg with TRF (p = 0.05), vs. +0.1 ± 4.3 kg with ND), with no significant change in fat-free mass. Exercise carbon dioxide production (VCO₂) and blood lactate concentration were significantly lower with the TRF intervention (p ≤ 0.02). No significant changes were seen in exercise respiratory exchange ratio or 10 km time trial performance (−00:20 ± 3:34 min:s TRF vs. −00:36 ± 2:57 min:s ND). Conclusion: This investigation demonstrated that adherence to a 4-week 16/8 TRF dietary intervention decreased fat mass and maintained fat-free mass, while not affecting running performance, in trained male endurance runners.

Metabolic and Molecular Subacute Effects of a Single Moderate-Intensity Exercise Bout, Performed in the Fasted State, in Obese Male Rats

Introduction and objectives: Obesity represents a major global public health problem. Its etiology is multifactorial and includes poor dietary habits, such as hypercaloric and hyperlipidic diets (HFDs), physical inactivity, and genetic factors. Regular exercise is, per se, a tool for the treatment and prevention of obesity, and recent studies suggest that the beneficial effects of exercise can be potentiated by the fasting state, thus potentially promoting additional effects. Despite the significant number of studies showing results that corroborate such hypothesis, very few have evaluated the effects of fasted-state exercise in overweight/obese populations. Therefore, the aim of this study was to evaluate the subacute effects (12 h after conclusion) of a single moderate-intensity exercise bout, performed in either a fed or an 8 h fasted state, on serum profile, substrate-content and heat shock pathway–related muscle protein immunocontent in obese male rats. Methods: Male Wistar rats received a modified high-fat diet for 12 weeks to induce obesity and insulin resistance. The animals were allocated to four groups: fed rest (FER), fed exercise (FEE), fasted rest (FAR) and fasted exercise (FAE). The exercise protocol was a 30 min session on a treadmill, with an intensity of 60% of VO₂max. The duration of the fasting period was 8 h prior to the exercise session. After a 12 h recovery, the animals were killed and metabolic parameters of blood, liver, heart, gastrocnemius and soleus muscles were evaluated, as well as SIRT1 and HSP70 immunocontent in the muscles. Results: HFD induced obesity and insulin resistance. Soleus glycogen concentration decreased in the fasted groups and hepatic glycogen decreased in the fed exercise group. The combination of exercise and fasting promoted a decreased concentration of serum total cholesterol and triglycerides. In the heart, combination fasting plus exercise was able to decrease triglycerides to control levels. In the soleus muscle, both fasting and fasting plus exercise were able to decrease triglyceride concentrations. In addition, heat shock protein 70 and sirtuin 1 immunocontent increased after exercise in the gastrocnemius and soleus muscles. Conclusions: An acute bout of moderate intensity aerobic exercise, when realized in fasting, may induce, in obese rats with metabolic dysfunctions, beneficial adaptations to their health, such as better biochemical and molecular adaptations that last for at least 12 h. Considering the fact that overweight/obese populations present an increased risk of cardiovascular events/diseases, significant reductions in such plasma markers of lipid metabolism are an important achievement for these populations.

Effects of Time-Restricted Feeding on Supramaximal Exercise Performance and Body Composition: A Randomized and Counterbalanced Crossover Study in Healthy Men

Using a crossover design, we explored the effects of both short- and long-term time-restricted feeding (TRF) vs. regular diet on Wingate (WnT) performance and body composition in well-trained young men. Twelve healthy male physical education students were included (age: 22.4 ± 2.8 years, height: 174.0 ± 7.1 cm, body mass: 73.6 ± 9.5 kg, body mass index: 24.2 ± 2.0 kg/m²). The order of dieting was randomized and counterbalanced, and all participants served as their own controls. TRF was limited to an 8-h eating window and non-TRF involved a customary meal pattern. Participants performed WnT tests and body composition scans at baseline, post-one and post-four weeks of the assigned diet. Before testing, participants were asked to fill out a dietary record over four consecutive days and were instructed to continue their habitual training throughout the study. Energy intake and macronutrient distribution were similar at baseline in both conditions. WnT mean power and total work output increased post-four weeks of TRF. Both conditions were similarly effective in increasing fat-free mass after four weeks of intervention. However, there was no correlation between change in fat-free mass and WnT mean power after TRF. TRF did not elicit any changes in WnT performance or body composition one week post-intervention. Thus, long-term TRF can be used in combination with regular training to improve supramaximal exercise performance in well-trained men.

Carbohydrate-Restricted Exercise With Protein Increases Self-Selected Training Intensity in Female Cyclists but Not Male Runners and Cyclists

ABSTRACT

Oosthuyse, T, Florence, GE, Correia, A, Smyth, C, and Bosch, AN. Carbohydrate-restricted exercise with protein increases self-selected training intensity in female cyclists but not male runners and cyclists. J Strength Cond Res 35(6): 1547-1558, 2021-Carbohydrate-restricted training challenges preservation of euglycemia and exercise intensity that precludes ergogenic gains, necessitating countering strategies. We investigated the efficacy of ingesting casein protein hydrolysate in overnight-fasted male runners, male cyclists, and female cyclists. Twenty-four overnight-fasted athletes ingested 15.8 g·h-1 casein hydrolysate or placebo-water during exercise (60-80 minutes) comprising an incremental test to exhaustion, steady-state exercise (70% Vmax or 60% peak power output, 87 ± 4% HRmax), and 20-minute time trial (TT) in a double-blind randomized crossover design, with p < 0.05 accepted as significant. Ingesting protein vs. placebo increased metabolic demand {oxygen consumption, +4.7% (95% confidence interval [CI] ± 4%), p = 0.0297; +3.2% (95% CI ± 3.4%), p = 0.061}, heart rate (p = 0.0083; p = 0.007) and rating of perceived exertion (RPE) (p = 0.0266; p = 0.0163) in male cyclists and runners, respectively, but not female cyclists. Protein vs. placebo increased carbohydrate oxidation (+0.26 [95% CI ± 0.13] g·min-1, p = 0.0007) in female cyclists alone. Cyclists reported +2 ± 1 higher RPE than runners (p = 0.0062). Glycemia was maintained only in runners and increased with protein vs. placebo after 20 minutes of steady-state exercise (+0.63 [95% CI ± 0.56] mmol·L-1, p = 0.0285). TT performance with protein vs. placebo ingestion was modestly compromised in runners (-2.8% [95% CI ± 2.2%], p = 0.0018), unchanged in male cyclists (+1.9% [95% CI ± 5.6%], p = 0.5794), and modestly improved in female cyclists (+2.5% [95% CI ± 1.8%], p = 0.0164). Casein hydrolysate ingestion during moderate to hard carbohydrate-restricted exercise increases glycemia in runners, but not cyclists. Casein hydrolysate increases metabolic demand in male athletes and carbohydrate oxidation in female cyclists and is suitable for improving carbohydrate-restricted training intensity in female but not male endurance athletes.

Considerations for Maximizing the Exercise "Drug" to Combat Insulin Resistance: Role of Nutrition, Sleep, and Alcohol

Insulin resistance is a key etiological factor in promoting not only type 2 diabetes mellitus but also cardiovascular disease (CVD). Exercise is a first-line therapy for combating chronic disease by improving insulin action through, in part, reducing hepatic glucose production and lipolysis as well as increasing skeletal muscle glucose uptake and vasodilation. Just like a pharmaceutical agent, exercise can be viewed as a "drug" such that identifying an optimal prescription requires a determination of mode, intensity, and timing as well as consideration of how much exercise is done relative to sitting for prolonged periods (e.g., desk job at work). Furthermore, proximal nutrition (nutrient timing, carbohydrate intake, etc.), sleep (or lack thereof), as well as alcohol consumption are likely important considerations for enhancing adaptations to exercise. Thus, identifying the maximal exercise "drug" for reducing insulin resistance will require a multi-health behavior approach to optimize type 2 diabetes and CVD care.

Carbohydrate improves exercise capacity but does not affect subcellular lipid droplet morphology, AMPK and p53 signalling in human skeletal muscle

KEY POINTS

Muscle glycogen and intramuscular triglycerides (IMTG, stored in lipid droplets) are important energy substrates during prolonged exercise. Exercise-induced changes in lipid droplet (LD) morphology (i.e. LD size and number) have not yet been studied under nutritional conditions typically adopted by elite endurance athletes, that is, after carbohydrate (CHO) loading and CHO feeding during exercise. We report for the first time that exercise reduces IMTG content in both central and peripheral regions of type I and IIa fibres, reflective of decreased LD number in both fibre types whereas reductions in LD size were exclusive to type I fibres. Additionally, CHO feeding does not alter subcellular IMTG utilisation, LD morphology or muscle glycogen utilisation in type I or IIa/II fibres. In the absence of alterations to muscle fuel selection, CHO feeding does not attenuate cell signalling pathways with regulatory roles in mitochondrial biogenesis.

ABSTRACT

We examined the effects of carbohydrate (CHO) feeding on lipid droplet (LD) morphology, muscle glycogen utilisation and exercise-induced skeletal muscle cell signalling. After a 36 h CHO loading protocol and pre-exercise meal (12 and 2 g kg^-1 , respectively), eight trained males ingested 0, 45 or 90 g CHO h^-1 during 180 min cycling at lactate threshold followed by an exercise capacity test (150% lactate threshold). Muscle biopsies were obtained pre- and post-completion of submaximal exercise. Exercise decreased (P < 0.01) glycogen concentration to comparable levels (∼700 to 250 mmol kg^-1 DW), though utilisation was greater in type I (∼40%) versus type II fibres (∼10%) (P < 0.01). LD content decreased in type I (∼50%) and type IIa fibres (∼30%) (P < 0.01), with greater utilisation in type I fibres (P < 0.01). CHO feeding did not affect glycogen or IMTG utilisation in type I or II fibres (all P > 0.05). Exercise decreased LD number within central and peripheral regions of both type I and IIa fibres, though reduced LD size was exclusive to type I fibres. Exercise induced (all P < 0.05) comparable AMPK^Thr172 (∼4-fold), p53^Ser15 (∼2-fold) and CaMKII^Thr268 phosphorylation (∼2-fold) with no effects of CHO feeding (all P > 0.05). CHO increased exercise capacity where 90 g h^-1 (233 ± 133 s) > 45 g h^-1 (156 ± 66 s; P = 0.06) > 0 g h^-1 (108 ± 54 s; P = 0.03). In conditions of high pre-exercise CHO availability, we conclude CHO feeding does not influence exercise-induced changes in LD morphology, glycogen utilisation or cell signalling pathways with regulatory roles in mitochondrial biogenesis.

Sucrose-Sweetened Drinks Reduce the Physical Performance and Increase the Cardiovascular Risk in Physically Active Males

INTRODUCTION

The intake of sugar-sweetened beverages (SSBs) has increased rapidly, but the effects of this habit on health and physical performance are unknown. This study assessed the effect of excessive SSB intake on biochemical, physical performance, and biochemical and cardiovascular parameters of physically active males.

METHODS

Seventeen volunteers consumed a placebo drink (Pd; carbohydrate free) and an excessive SSB drink (eSSBd = Pd plus 300 g sucrose). In a blind randomized crossover study, the subjects were assigned to Pd or eSSBd groups for 15 days. After an interval of 7 days, subjects were reassigned to the other condition.

RESULTS

After eSSBd intake, there was an increase in weight (69.34 ± 13.71 vs. 70.62 ± 14.06), body mass index (24.49 ± 4.01 vs. 24.97 ± 4.13), waist circumference (75.33 ± 11.22 vs. 76.79 ± 11.51), VLDL (19.54 ± 9.50 vs. 25.52 ± 11.18), triglycerides (78.94 ± 23.79 vs. 114.77 ± 43.65), and peak systolic blood pressure (178.57 ± 26.56 vs. 200.71 ± 24.64). The cardiorespiratory response to exercise (VO2max) (48.15 ± 10.42 vs. 40.98 ± 11.20), peak heart rate (186.64 ± 8.00 vs. 179.64 ± 6.28), total exercise time (15.02 ± 1.57 vs. 14.00 ± 2.18), and mechanical work (15.83 ± 4.53 vs. 13.68 ± 5.67) decreased after eSSBd intake (all values expressed in initial mean ± DP vs. final). The rates of perceived exertion were higher (1.300 vs.1.661 slope and -0.7186 vs. -1.118 y-intercept) after eSSBd intake.

CONCLUSION

The present study shows that 15 days of eSSBd intake may negatively modulate biochemical parameters associated with cardiovascular risk. In addition, this overintake can impair the physical performance and cardiovascular responses to physical exercise.

Bicarbonate Unlocks the Ergogenic Action of Ketone Monoester Intake in Endurance Exercise

PURPOSE

We recently reported that oral ketone ester (KE) intake before and during the initial 30 min of a 3 h 15 min simulated cycling race (RACE) transiently decreased blood pH and bicarbonate without affecting maximal performance in the final quarter of the event. We hypothesized that acid-base disturbances due to KE overrules the ergogenic potential of exogenous ketosis in endurance exercise.

METHODS

Nine well-trained male cyclists participated in a similar RACE consisting of 3 h submaximal intermittent cycling (IMT180') followed by a 15-min time trial (TT15') preceding an all-out sprint at 175% of lactate threshold (SPRINT). In a randomized crossover design, participants received (i) 65 g KE, (ii) 300 mg·kg-1 body weight NaHCO3 (BIC), (iii) KE + BIC, or (iv) a control drink (CON), together with consistent 60 g·h-1 carbohydrate intake.

RESULTS

KE ingestion transiently elevated blood D-ß-hydroxybutyrate to ~2-3 mM during the initial 2 h of RACE (P < 0.001 vs CON). In KE, blood pH concomitantly dropped from 7.43 to 7.36 whereas bicarbonate decreased from 25.5 to 20.5 mM (both P < 0.001 vs CON). Additional BIC resulted in 0.5 to 0.8 mM higher blood D-ß-hydroxybutyrate during the first half of IMT180' (P < 0.05 vs KE) and increased blood bicarbonate to 31.1 ± 1.8 mM and blood pH to 7.51 ± 0.03 by the end of IMT180' (P < 0.001 vs KE). Mean power output during TT15' was similar between KE, BIC, and CON at ~255 W but was 5% higher in KE + BIC (P = 0.02 vs CON). Time to exhaustion in the sprint was similar between all conditions at ~60 s (P = 0.88). Gastrointestinal symptoms were similar between groups.

DISCUSSION

The coingestion of oral bicarbonate and KE enhances high-intensity performance at the end of an endurance exercise event without causing gastrointestinal distress.

Influence of high-intensity interval training and intermittent fasting on myocardium apoptosis pathway and cardiac morphology of healthy rats

AIM

To evaluate the influence of intermittent fasting and high-intensity interval training (HIIT) on myocardial apoptosis signaling and cardiac morphological characteristics in healthy rats.

METHODS

Male Wistar rats (n = 60) were divided into four groups: sedentary control (SED-C), intermittent fasting (SED-IF), high-intensity interval training (HIIT-C), and high-intensity interval training plus intermittent fasting (HIIT-IF). SED-C and HIIT-C groups were treated daily with ad libitum chow; SED-IF and HIIT-IF received the same standard chow every other day. HIIT-C and HIIT-IF rats were submitted to an HIIT protocol five times a week for 12 weeks. At the end of the experiment, functional capacity, cardiac morphology, and expression of apoptosis signaling pathways-related proteins were analyzed.

KEY FINDINGS

HIIT increased cardiomyocyte cross-sectional area, collagen interstitial fraction, and the pro-apoptotic proteins AIF and caspase-3 expression, and reduced pro-apoptotic protein CYTC expression and the cleaved-to-non-cleaved PARP-1 ratio in myocardium. Intermittent fasting reduced cardiomyocyte cross-sectional area, collagen interstitial fraction, and expression of Bax, CYTC and cleaved PARP-1, and increased expression of the anti-apoptotic protein BCL-2. SMAC, ARC, and caspase-8 expression was not changed by HIIT or intermittent fasting.

SIGNIFICANCE

HIIT promotes cardiomyocyte hypertrophy and interstitial fibrosis, and modulates the apoptosis signaling pathway in healthy rat myocardium. Intermittent fasting reduces pro-apoptotic and increases antiapoptotic signaling, besides attenuating HIIT-induced cardiomyocyte hypertrophy and myocardial interstitial fibrosis.

Tuning fatty acid oxidation in skeletal muscle with dietary fat and exercise

Both the consumption of a diet rich in fatty acids and exercise training result in similar adaptations in several skeletal muscle proteins. These adaptations are involved in fatty acid uptake and activation within the myocyte, the mitochondrial import of fatty acids and further metabolism of fatty acids by β-oxidation. Fatty acid availability is repeatedly increased postprandially during the day, particularly during high dietary fat intake and also increases during, and after, aerobic exercise. As such, fatty acids are possible signalling candidates that regulate transcription of target genes encoding proteins involved in muscle lipid metabolism. The mechanism of signalling might be direct or indirect targeting of peroxisome proliferator-activated receptors by fatty acid ligands, by fatty acid-induced NAD⁺-stimulated activation of sirtuin 1 and/or fatty acid-mediated activation of AMP-activated protein kinase. Lactate might also have a role in lipid metabolic adaptations. Obesity is characterized by impairments in fatty acid oxidation capacity, and individuals with obesity show some rigidity in increasing fatty acid oxidation in response to high fat intake. However, individuals with obesity retain improvements in fatty acid oxidation capacity in response to exercise training, thereby highlighting exercise training as a potential method to improve lipid metabolic flexibility in obesity.

Low-carbohydrate diets: Effects on metabolism and exercise - A comprehensive literature review

BACKGROUND & AIMS

Low-carbohydrate diets (LCD) have gained substantial attention in recent years for their potential in health promotion and treatment of diseases, but they remain controversial in nutrition guidelines and exercise performance. Herein, through a literature review, we discuss the current evidence base by considering management of LCD and potential coupling of these dietary regiments with physical exercise.

METHODS

We performed a comprehensive literature review with no date limits as a means of including seminal to current studies.

RESULTS

Reduction of CHO intake decreases muscle glycogen, yielding greater fat oxidation and associated metabolic benefits. LCD may promote fat mass loss and regulation of biochemical parameters, such as lipid and glycemic biomarkers. The therapeutic potential of LCD towards noncommunicable diseases, particularly obesity and its comorbidities, is therefore reasonable as a dietary candidate in this context. Potential benefits to this approach are linked to enhancement of mitochondrial gene expression and mitochondrial biogenesis. As such, LCD may be a feasible tool in a 'periodized nutrition' for athletes and within clinical scenarios. Long-term observational follow-up studies have demonstrated increased mortality and cardiovascular implications of LCD. However, harmful associations may depend on the food source (e.g., animal-based vs. plant-based foods).

CONCLUSION

LCD may decrease body mass, waist circumference, and improve fat and carbohydrate metabolism. When combined with exercise, LCD seems to be an effective strategy in regulating metabolic factors of cardiovascular diseases. Conversely, LCD may be associated with higher mortality and metabolic dysregulations if it contains large amounts of animal-based foods, particularly saturated fat.

What Should I Eat before Exercise? Pre-Exercise Nutrition and the Response to Endurance Exercise: Current Prospective and Future Directions

The primary variables influencing the adaptive response to a bout of endurance training are exercise duration and exercise intensity. However, altering the availability of nutrients before and during exercise can also impact the training response by modulating the exercise stimulus and/or the physiological and molecular responses to the exercise-induced perturbations. The purpose of this review is to highlight the current knowledge of the influence of pre-exercise nutrition ingestion on the metabolic, physiological, and performance responses to endurance training and suggest directions for future research. Acutely, carbohydrate ingestion reduces fat oxidation, but there is little evidence showing enhanced fat burning capacity following long-term fasted-state training. Performance is improved following pre-exercise carbohydrate ingestion for longer but not shorter duration exercise, while training-induced performance improvements following nutrition strategies that modulate carbohydrate availability vary based on the type of nutrition protocol used. Contrasting findings related to the influence of acute carbohydrate ingestion on mitochondrial signaling may be related to the amount of carbohydrate consumed and the intensity of exercise. This review can help to guide athletes, coaches, and nutritionists in personalizing pre-exercise nutrition strategies, and for designing research studies to further elucidate the role of nutrition in endurance training adaptations.

Short-Term, Combined Fasting and Exercise Improves Body Composition in Healthy Males

Fasting enhances the beneficial metabolic outcomes of exercise; however, it is unknown whether body composition is favorably modified on the short term. A baseline-follow-up study was carried out to assess the effect of an established protocol involving short-term combined exercise with fasting on body composition. One hundred seven recreationally exercising males underwent a 10-day intervention across 15 fitness centers in the Netherlands involving a 3-day gradual decrease of food intake, a 3-day period with extremely low caloric intake, and a gradual 4-day increase to initial caloric intake, with daily 30-min submaximal cycling. Using dual-energy X-ray absorptiometry analysis, all subjects substantially lost total body mass (-3.9 ± 1.9 kg; p < .001) and fat mass (-3.3 ± 1.3 kg; p < .001). Average lean mass was lost (-0.6 ± 1.5 kg; p < .001), but lean mass as a percentage of total body mass was not reduced. The authors observed a loss of -3.9 ± 1.9% android fat over total fat mass (p < .001), a loss of -2.2 ± 1.9% gynoid over total fat mass (p < .001), and reduced android/gynoid ratios (-0.05 ± 0.1; p < .001). Analyzing 15 preselected single-nucleotide polymorphisms in 13 metabolism-related genes revealed trending associations for thyroid state-related single-nucleotide polymorphisms rs225014 (deiodinase 2) and rs35767 (insulin-like growth factor1), and rs1053049 (PPARD). In conclusion, a short period of combined fasting and exercise leads to a substantial loss of body and fat mass without a loss of lean mass as a percentage of total mass.

Carbohydrate Consumption and Periodization Strategies Applied to Elite Soccer Players

PURPOSE OF REVIEW

During a soccer season, athletes tend to play intense and light matches such as decisive and qualifying games. The amount of muscle glycogen stores is a determining factor of performance during exercise, and manipulation of carbohydrate intake during the soccer season to enhance muscle glycogen stores can improve the performance of elite soccer players. The purpose of this review is to provide a holistic view of the periodization of carbohydrates and their effects on sports performance, based on what the literature recommends for the periodization of carbohydrates for endurance athletes, and of muscle glycogen recovery and compensation among professional soccer players.

RECENT FINDINGS

The ingestion of large amounts of carbohydrates (CHO;10 g/kg of body weight (BW)/day) is important 36 h before a match for the elite soccer player to ensure muscle glycogen supercompensation. In addition, elite soccer players should intake 1 to 1.5 g/kg BW/h within the first 4 h after a soccer game to maximize glycogen resynthesis. However, the season is comprised of away and home games that require different intensities; thus, soccer players need to periodize CHO intake based on evidence-based recommendations such as "train low," "train low, compete high," and/or "sleep low." The goal is to induce training adaptations by alternating with high or low CHO availability based on seasons, matches, and training intensities. The strategy can result in improved performance during games. Periodizing the consumption of carbohydrates, based on the intensity of training and matches, should include more carbohydrates when the matches require higher intensity and fewer carbohydrates when they require lower intensity; this is a strategy that will improve the performance of elite soccer athletes.

Supplement with whey protein hydrolysate in contrast to carbohydrate supports mitochondrial adaptations in trained runners

Background

Protein supplementation has been suggested to augment endurance training adaptations by increasing mixed muscle and myofibrillar protein synthesis and lean body mass. However, a potential beneficial effect on mitochondrial adaptations is yet to be clarified.

The aim of the present study was to investigate the effect of consuming whey protein hydrolysate before and whey protein hydrolysate plus carbohydrate (PRO-CHO) after each exercise session during a six-week training period compared to similarly timed intake of isocaloric CHO supplements on biomarkers of mitochondrial biogenesis, VO_2max and performance in trained runners.

Methods

Twenty-four trained runners (VO_2max 60.7 ± 3.7 ml O₂ kg^− 1 min¹) completed a six-week block randomized controlled intervention period, consisting of progressive running training. Subjects were randomly assigned to either PRO-CHO or CHO and matched in pairs for gender, age, VO_2max, training and performance status. The PRO-CHO group ingested a protein beverage (0.3 g kg^− 1) before and protein-carbohydrate beverage (0.3 g protein kg^− 1 and 1 g carbohydrate kg^− 1) after each exercise session. The CHO group ingested an energy matched carbohydrate beverage. Resting muscle biopsies obtained pre and post intervention were analyzed for mitochondrial specific enzyme activity and mitochondrial protein content. Subjects completed a 6 K time trial (6 K TT) and a VO_2max test pre, midway (only 6 K TT) and post intervention.

Results

Following six weeks of endurance training Cytochrome C (Cyt C) protein content was significantly higher in the PRO-CHO group compared to the CHO group (p < 0.05), with several other mitochondrial proteins (Succinate dehydrogenase (SDHA), Cytochrome C oxidase (COX-IV), Voltage-dependent anion channel (VDAC), Heat shock protein 60 (HSP60), and Prohibitin (PHB1)) following a similar, but non-significant pattern (p = 0.07–0.14). β-hydroxyacyl-CoA dehydrogenase (HAD) activity was significantly lower after training in the CHO group (p < 0.01), but not in the PRO-CHO group (p = 0.24). VO_2max and 6 K TT was significantly improved after training with no significant difference between groups.

Conclusion

Intake of whey PRO hydrolysate before and whey PRO hydrolysate plus CHO after each exercise session during a six-week endurance training period may augment training effects on specific mitochondrial proteins compared to intake of iso-caloric CHO but does not alter VO_2max or 6 K TT performance.

Trial registration

clinicaltrials.gov, NCT03561337. Registered 6 June 2018 – Retrospectively registered.

Prevalence and Determinants of Fasted Training in Endurance Athletes: A Survey Analysis

Athletes may choose to perform exercise in the overnight-fasted state for a variety of reasons related to convenience, gut comfort, or augmenting the training response, but it is unclear how many endurance athletes use this strategy. We investigated the prevalence and determinants of exercise performed in the overnight-fasted state among endurance athletes using an online survey and examined differences based on sex, competitive level, and habitual dietary pattern. The survey was completed by 1,950 endurance athletes (51.0% female, mean age 40.9 ± 11.1 years). The use of fasted training was reported by 62.9% of athletes, with significant effects of sex (p < .001, Cramer’s V [φc] = 0.18, 90% CI [0.14, 0.22]), competitive level (p < .001, φc = 0.09, 90% CI [0.5, 0.13]), and habitual dietary pattern noted (p < .001, φc = 0.26, 90% CI [0.22, 0.29]). Males, nonprofessional athletes, and athletes following a low-carbohydrate, high-fat diet were most likely to perform fasted training. The most common reasons for doing so were related to utilizing fat as a fuel source (42.9%), gut comfort (35.5%), and time constraints/convenience (31.4%), whereas the most common reasons athletes avoided fasted training were that it does not help their training (47.0%), performance was worse during fasted training (34.7%), or greater hunger (34.6%). Overall, some athletes perform fasted training because they think it helps their training, whereas others avoid it because they think it is detrimental to their training goals, highlighting a need for future research. These findings offer insights into the beliefs and practices related to fasted-state endurance training.

Exercising your fat (metabolism) into shape: a muscle-centred view

Fatty acids are an important energy source during exercise. Training status and substrate availability are determinants of the relative and absolute contribution of fatty acids and glucose to total energy expenditure. Endurance-trained athletes have a high oxidative capacity, while, in insulin-resistant individuals, fat oxidation is compromised. Fatty acids that are oxidised during exercise originate from the circulation (white adipose tissue lipolysis), as well as from lipolysis of intramyocellular lipid droplets. Moreover, hepatic fat may contribute to fat oxidation during exercise. Nowadays, it is clear that myocellular lipid droplets are dynamic organelles and that number, size, subcellular distribution, lipid droplet coat proteins and mitochondrial tethering of lipid droplets are determinants of fat oxidation during exercise. This review summarises recent insights into exercise-mediated changes in lipid metabolism and insulin sensitivity in relation to lipid droplet characteristics in human liver and muscle. Graphical abstract.

Five Evidence-Based Lifestyle Habits People With Diabetes Can Use

Several evidence-based lifestyle habits focusing on the composition, timing, and sequence of meals and on pre- and postmeal exercise can improve diabetes management. Consuming low-carbohydrate, balanced meals and eating most carbohydrates early in the day are helpful habits. Eating the protein and vegetable components of a meal first and consuming the carbohydrates 30 minutes later can moderate glucose levels. Postmeal glucose surges can be blunted without precipitating hypoglycemia with moderate exercise 30-60 minutes before the anticipated peak. Short-duration, high-intensity exercise could also be effective. Premeal exercise can improve insulin sensitivity but can also cause post-exertion glucose elevations. Moreover, high-intensity premeal exercise may precipitate delayed hypoglycemia in some people. Glycemia benefits can be enhanced by eating a light, balanced breakfast after premeal exercise.

The Role of Nutri(epi)genomics in Achieving the Body's Full Potential in Physical Activity

Physical activity represents a powerful tool to achieve optimal health. The overall activation of several molecular pathways is associated with many beneficial effects, mainly converging towards a reduced systemic inflammation. Not surprisingly, regular activity can contribute to lowering the “epigenetic age”, acting as a modulator of risk toward several diseases and enhancing longevity. Behind this, there are complex molecular mechanisms induced by exercise, which modulate gene expression, also through epigenetic modifications. The exercise-induced epigenetic imprint can be transient or permanent and contributes to the muscle memory, which allows the skeletal muscle adaptation to environmental stimuli previously encountered. Nutrition, through key macro- and micronutrients with antioxidant properties, can play an important role in supporting skeletal muscle trophism and those molecular pathways triggering the beneficial effects of physical activity. Nutrients and antioxidant food components, reversibly altering the epigenetic imprint, have a big impact on the phenotype. This assigns a role of primary importance to nutri(epi)genomics, not only in optimizing physical performance, but also in promoting long term health. The crosstalk between physical activity and nutrition represents a major environmental pressure able to shape human genotypes and phenotypes, thus, choosing the right combination of lifestyle factors ensures health and longevity.

Diurnal variation in the glycogen content of the human liver using 13 C MRS

Glycogen in tissues functions not only as carbohydrate reserves, but also as molecular sensors capable of activating signaling pathways in response to physical activity. While glycogen in the skeletal muscles is mainly a local energy substrate, glycogen in the liver serves as a glucose reserve to maintain normal blood glucose levels in the body, even during the sleep state. The aim of this study is to compare the diurnal variation of glycogen in the muscle and liver of human subjects under normal conditions. The glycogen content was measured in the muscle and liver of 10 young, healthy, male volunteers using ¹³ C MRS, a non-invasive technique. The subjects remained sedentary, and glycogen concentration was measured six times daily. Experimental meals were provided to achieve individual energy balance, estimated according to the energy requirement guideline for patients from Japan. The largest variation in muscle glycogen compared with 1 h after supper (20:00 on Day 1) was 3.1 ± 8.2 mmol/L (16:00 on Day 2). In the liver, however, the glycogen content decreased by 80.6 ± 40.4 mmol/L through the overnight fasting period (07:00 on Day 2). This study demonstrated that the glycogen content in the liver was significantly lower in the morning, while the glycogen content in the calf muscles underwent minimal diurnal variation. The overnight fast is a characteristic daily condition, in which liver glycogen content is low, whereas muscle glycogen content is relatively unaffected.

Taurine Supplementation Increases Post-Exercise Lipid Oxidation at Moderate Intensity in Fasted Healthy Males

Based on the fact that taurine can increase lipid metabolism, the objective of the present study was to evaluate the effects of different doses of acute taurine supplementation on lipid oxidation levels in healthy young men after a single bout of fasting aerobic exercise. A double-blind, acute, and crossover study design was conducted. Seventeen men (age 24.8 ± 4.07y; BMI: 23.9 ± 2.57 kg/m²) participated in the present study. Different doses of taurine (TAU) (3 g or 6 g) or placebo were supplemented 90 min before a single bout of fasting aerobic exercise (on a treadmill at 60% of VO₂ max). The subjects performed three trials, and each one was separated by seven days. Blood samples were collected at baseline and after the exercise protocol of each test to analyze plasma levels of glycerol and taurine. Lipid and carbohydrate oxidation were determined immediately after exercise for 15 min by indirect calorimetry. We observed that TAU supplementation (6 g) increased lipid oxidation (38%) and reduced the respiratory coefficient (4%) when compared to the placebo (p < 0.05). However, no differences in lipid oxidation were observed between the different doses of taurine (3 g and 6 g). For glycerol concentrations, there were no differences between trials. Six grams of TAU supplementation 90 min before a single bout of aerobic exercise in a fasted state was sufficient to increase the lipid oxidation post-exercise in healthy young men.

Exogenous ketosis impacts neither performance nor muscle glycogen breakdown in prolonged endurance exercise

Available evidence indicates that ketone bodies inhibit glycolysis in contracting muscles. Therefore, we investigated whether acute exogenous ketosis by oral ketone ester (KE) intake early in a simulated cycling race can induce transient glycogen sparing by glycolytic inhibition, thereby increasing glycogen availability in the final phase of the event. In a randomized crossover design, 12 highly trained male cyclists completed a simulated cycling race (RACE), which consisted of 3-h intermittent cycling (IMT_180′), a 15-min time trial (TT_15′), and a maximal sprint (SPRINT). During RACE, subjects received 60 g carbohydrates/h combined with three boluses (25, 20, and 20 g) (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE) or a control drink (CON) at 60 and 20 min before and at 30 min during RACE. KE intake transiently increased blood d-β-hydroxybutyrate to ~3 mM (range: 2.6–5.2 mM) during the first half of RACE (P < 0.001 vs. CON). Blood pH concomitantly decreased from approximately 7.42 to 7.36 (range: 7.29–7.40), whereas bicarbonate dropped from 26.0 to 21.6 mM (range: 20.1–23.7; both P < 0.001 vs. CON)_. Net muscle glycogen breakdown during IMT_180′ [KE: −78 ± 30 (SD); CON: −60 ± 22 mmol/kg wet wt; P = 0.08] and TT_15′ (KE: −9 ± 18; CON: −18 ± 18 mmol/kg wet wt; P = 0.35) was similar between KE and CON. Accordingly, mean power output during TT_15′ (KE: 273 ± 38; CON: 272 ± 37 W; P = 0.83) and time-to-exhaustion in the SPRINT (KE: 59 ± 16; CON: 58 ± 17 s; P = 0.66) were similar between conditions. In conclusion, KE intake during a simulated cycling race does not cause glycogen sparing, nor does it affect all-out performance in the final stage of a simulated race.

NEW & NOTEWORTHY Exogenous ketosis produced by oral ketone ester ingestion during the early phase of prolonged endurance exercise and against the background of adequate carbohydrate intake neither causes muscle glycogen sparing nor improves performance in the final stage of the event. However, such exogenous ketosis may decrease buffering capacity in the approach of the final episode of the event. Furthermore, ketone ester intake during exercise may reduce appetite immediately after exercise.

Mendonca G. Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis

Intermittent fasting (IF) has been studied in athletes during Ramadan and in those willing to decrease adiposity while maintaining or increasing lean body mass. The purpose of this systematic review was to summarize the effects of IF on performance outcomes. We searched peer-reviewed articles in the following databases: PubMed, Web of Science and Sport Discus (up to December 2019). Studies were selected if they included samples of adults (≥18 years), had an experimental or observational design, investigated IF (Ramadan and time-restricted feeding (TRF)), and included performance outcomes. Meta-analytical procedures were conducted when feasible. Twenty-eight articles met the eligibility criteria. Findings indicated that maximum oxygen uptake is significantly enhanced with TRF protocols (SMD = 1.32, p = 0.001), but reduced with Ramadan intermittent fasting (Ramadan IF; SMD = −2.20, p < 0.001). Additional effects of IF may be observed in body composition (body mass and fat mass). Non-significant effects were observed for muscle strength and anaerobic capacity. While Ramadan IF may lead to impairments in aerobic capacity, TRF may be effective for improving it. As there are few studies per performance outcome, more research is needed to move the field forward.