Re-examination of the contribution of substrates to energy expenditure during high-intensity intermittent exercise in endurance athletes

The Prevalence of Low Energy Availability in Cross-Country Skiers during the Annual Cycle

BACKGROUND AND OBJECTIVES

A sustained mismatch between energy intake (EI) and exercise energy expenditure (EEE) can lead to Low Energy Availability (LEA), as well as health and performance impairments characteristic of Relative Energy Deficiency in Sport (RED-S). Research in females has identified specific LEA cut-points for the risks of developing physiological and performance disturbances. Cut-points in males have yet to be evaluated; therefore, this study examined the prevalence of LEA in highly trained male cross-country skiers. The key purpose of this study was to analyze EI, resting energy expenditure (REE), EEE, and energy availability (EA) in highly trained cross-country skiers during the preparation and competition periods. The secondary objective of our study was to evaluate the relative contribution of fats and carbohydrates to EI, REE, and EEE.

MATERIALS AND METHODS

EI was determined by an estimated 24 h diet recall method, REE was assessed by indirect calorimetry, and EEE was estimated from heart rate in 27 cross-country skiers.

RESULTS

EI amounted to 4050 ± 797 kcal/day on a typical training day (TD) and 5986 ± 924 kcal/day (p < 0.001) on a typical competition day (CD). REE on TDs (2111 ± 294 kcal/day or 30 ± 6 kcal/day/kg) was higher (p < 0.05) than on CDs (1891 ± 504 kcal/day or 27 ± 7 kcal/day/kg). The EA in the athletes was <15 kcal∙kg FFM-1·d-1 on TDs and <65 kcal∙kg FFM-1·d-1 on CDs. EI was not optimal, as indicated by low EA throughout TDs (June). This could be associated with insufficient EI along with a high amount of EEE (3690.7 ± 485.2 kcal/day). During the transition from TD to CD, an increase in the contribution of fats to EI and EEE was observed in cross-country skiers.

CONCLUSION

The conception of LEA and REDs and their potential implication for performance is underestimated among coaches and athletes. The importance of appropriate dietary strategies is essential to ensure that enough calories are consumed to support efficient training.

Genotypic and Allelic Distribution of the CD36 rs1761667 Polymorphism in High-Level Moroccan Athletes: A Pilot Study

Previous studies have shown that variations in the CD36 gene may affect phenotypes associated with fat metabolism as the CD36 protein facilitates the transport of fatty acids to the mitochondria for oxidation. However, no previous study has tested whether variations in the CD36 gene are associated with sports performance. We investigated the genotypic and allelic distribution of the single-nucleotide polymorphism (SNP) rs1761667 in the CD36 gene in elite Moroccan athletes (cyclists and hockey players) in comparison with healthy non-athletes of the same ethnic origin. Forty-three Moroccan elite male athletes (nineteen cyclists and twenty-four field hockey players) belonging to the national teams of their respective sports (athlete group) were compared to twenty-eight healthy, active, male university students (control group). Genotyping of the CD36 rs1761667 (G>A) SNP was performed via polymerase chain reaction (PCR) and Sanger sequencing. A chi-square (χ2) test was used to assess the Hardy-Weinberg equilibrium (HWE) and to compare allele and genotype frequencies in the "athlete" and "control" groups. The genotypic distribution of the CD36 rs1761667 polymorphism was similar in elite athletes (AA: 23.81, AG: 59.52, and GG: 16.67%) and controls (AA: 19.23, AG: 69.23, and GG: 11.54%; χ2 = 0.67, p = 0.71). However, the genotypic distribution of the CD36 rs1761667 polymorphism was different between cyclists (AA: 0.00, AG: 72.22, and GG: 27.78%) and hockey players (AA: 41.67, AG: 50.00, and GG: 8.33%; χ2 = 10.69, p = 0.004). Specifically, the frequency of the AA genotype was significantly lower in cyclists than in hockey players (p = 0.02). In terms of allele frequency, a significant difference was found between cyclists versus field hockey players (χ2 = 7.72, p = 0.005). Additionally, there was a predominance of the recessive model in cyclists over field hockey players (OR: 0.00, 95% CI: 0.00-0.35, p = 0.002). Our study shows a significant difference between cyclists and field hockey players in terms of the genotypic and allelic frequency of the SNP rs1761667 of the CD36 gene. This divergence suggests a probable association between genetic variations in the CD36 gene and the type of sport in elite Moroccan athletes.

Impact of aerobic fitness status, menstrual cycle phase, and oral contraceptive use on exercise substrate oxidation and metabolic flexibility in females

The influence of menstrual cycle phase and fitness status on metabolism during high-intensity interval exercise (HIIE) was assessed. Twenty-five females (24.4 (3.6) years) were categorized by normal menstrual cycle (n = 14) vs. oral contraceptive (OC) use (n = 11) and by aerobic fitness, high-fitness females (HFF; n = 13) vs. low-fitness females (LFF; n = 12). HIIE was four sets of four repetitions with a 3 min rest between intervals on a cycle ergometer at a power output halfway between the ventilatory threshold and V̇O2peak and performed during follicular (FOL: days 2-7 or inactive pills) and luteal phases (LUT: day ∼21 or 3rd week of active pills). Substrate oxidation was assessed via indirect calorimetry, blood lactate via finger stick, and recovery of skeletal muscle oxidative metabolism (mV̇O2) via continuous-wave near-infrared spectroscopy. HFF oxidized more fat (g·kg-1) during the full session (FOL: p = 0.050, LUT: p = 0.001), high intervals (FOL: p = 0.048, LUT: p = 0.001), low intervals (FOL: p = 0.032, LUT: p = 0.024), and LUT recovery (p = 0.033). Carbohydrate oxidation area under the curve was greater in HFF during FOL (FOL: p = 0.049, LUT: p = 0.124). Blood lactate was lower in LFF in FOL (p ≤ 0.05) but not in LUT. Metabolic flexibility (Δ fat oxidation g·kg-1·min-1) was greater in HFF than LFF during intervals 2-3 in FOL and 1-4 in LUT (p ≤ 0.05). Fitness status more positively influences exercise metabolic flexibility during HIIE than cycle phase or OC use.

Supplementation with food-derived oligopeptides promotes lipid metabolism in young male cyclists: a randomized controlled crossover trial

BACKGROUND

Accumulation of body fat and dyslipidemia are associated with the development of obesity and cardiometabolic diseases. Moreover, the degree to which lipids can be metabolized has been cited as a determinant of cardiometabolic health and prolonged endurance capacity. In the backdrop of increasing obesity and cardiometabolic diseases, lipid metabolism and its modulation by physical activity, dietary adjustments, and supplementation play a significant role in maintaining health and endurance. Food-derived oligopeptides, such as rice and soybean peptides, have been shown to directly regulate abnormal lipid metabolism or promote hypolipidemia and fat oxidation in cell culture models, animal models, and human studies. However, whether supplementation with oligopeptides derived from multiple food sources can promote lipid degradation and fat oxidation in athletes remains unclear. Therefore, in a randomized controlled crossover trial, we investigated the impact of food-derived oligopeptide supplementation before and during exercise on lipid metabolism in young male cyclists.

METHODS

Sixteen young male cyclists (age: 17.0 ± 1.0 years; height: 178.4 ± 6.9 cm; body mass: 68.7 ± 12.7 kg, body mass index: 21.5 ± 3.4 kg/m2; maximum oxygen uptake: 56.3 ± 5.8 mL/min/kg) participated in this randomized controlled crossover trial. Each participant drank two beverages, one containing a blend of three food-derived oligopeptides (treatment, 0.5 g/kg body weight in total) and the other without (control), with a 2-week washout period between two experiments. The cyclists completed a one-day pattern protocol that consisted of intraday fasting, 30 min of sitting still, 85 min of prolonged exercise plus a 5-min sprint (PE), a short recovery period of 60 min, a 20-min time trial (TT), and recovery till next morning. Blood samples were collected for biochemical analyses of serum lipids and other biomarkers. We analyzed plasma triglyceride species (TGs), free amino acids (FAAs), and tricarboxylic acid (TCA) cycle intermediates using omics methods. In addition, exhaled gas was collected to assess the fat oxidation rate.

RESULTS

Five of 20 plasma FAAs were elevated pre-exercise (pre-Ex) only 20 min after oligopeptide ingestion, and most FAAs were markedly increased post PE and TT. Serum levels of TG and non-esterified fatty acids were lower in the experimental condition than in the control condition at the post PE and TT assessments, respectively. Further, the omics analysis of plasma TGs for the experimental condition demonstrated that most TGs were lower post PE and at the next fasting when compared with control levels. Simultaneously, the fat oxidation rate began to increase only 20 min after ingestion and during the preceding 85 min of PE. Levels of TCA cycle intermediates did not differ between the conditions.

CONCLUSIONS

The study noted that continuous ingestion of food-derived oligopeptides accelerated total body triglyceride breakdown, non-esterified fatty acid uptake, and fat oxidation during both sedentary and exercise states. Elevated circulating and intracellular FAA flux may modulate the selection of substrates for metabolic pathways in conjunction with the release of neuroendocrinological factors that slow down carbohydrate metabolism via acetyl coenzyme A feedback inhibition. This may increase the availability of fatty acids for energy production, with FAAs supplying more substrates for the TCA cycle. The findings of this study provide novel insight into strategies for promoting lipid metabolism in populations with dyslipidemia-related metabolic disorders such as obesity and for improving physiological functioning during endurance training. However, the absence of a non-exercising control group and verification of long-term supplementation effects was a limitation. Future studies will emphasize the impacts of whole protein supplementation as a control and of combined food-derived peptides or oligopeptides with probiotics and healthy food components on lipid metabolism in individuals who exercise.

The Effects of HIIT vs. MICT and Sedentary Controls on Blood Lipid Concentrations in Nondiabetic Overweight and Obese Young Adults: A Meta-analysis

With rates of obesity and dyslipidemia rising among young adults, this meta-analysis aimed to compare the effects of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) and sedentary controls (CON) on low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride (TG), and total cholesterol (TC) in nondiabetic overweight and obese young adults to determine if HIIT or MICT is more efficacious in improving dyslipidemia. Studies included in the analysis had to be randomized controlled trials or quasi-experimental studies, comparing the effects of HIIT versus MICT or CON on at least three variables of interest: LDL, HDL, TG, and TC, in nondiabetic adults, with body mass indexes (BMIs) above 25, and average ages between 18-30. The quality of the studies was evaluated using the Physiotherapy Evidence Database (PEDro) scale. Eight studies fulfilled the selection criteria, with a mean PEDro quality score of 5.8. Compared to CON, HIIT significantly decreased the concentrations of LDL (-12.14 mg/dL, p = < 0.00001) and TC (-9.27 mg/dL, p = 0.003), without significantly affecting HDL or TG. Compared to MICT, HIIT significantly decreased the concentrations of LDL (-6.23 mg/dL, p = 0.05) and TC (-7.85 mg/dL, p = 0.02), without significantly affecting HDL or TG concentrations. HIIT is superior to MICT and CON in improving the concentrations of LDL and TC in our target population. As early management of dyslipidemia improves long-term health, we recommend clinicians consider HIIT training protocols for their nondiabetic overweight and obese young adult patients.

FAT/CD36 Participation in Human Skeletal Muscle Lipid Metabolism: A Systematic Review

Fatty acid translocase/cluster of differentiation 36 (FAT/CD36) is a multifunctional membrane protein activated by a high-fat diet, physical exercise, fatty acids (FAs), leptin, and insulin. The principal function of FAT/CD36 is to facilitate the transport of long-chain fatty acids through cell membranes such as myocytes, adipocytes, heart, and liver. Under high-energy expenditure, the different isoforms of FAT/CD36 in the plasma membrane and mitochondria bind to the mobilization and oxidation of FAs. Furthermore, FAT/CD36 is released in its soluble form and becomes a marker of metabolic dysfunction. Studies with healthy animals and humans show that physical exercise and a high-lipid diet increase FAT/CD36 expression and caloric expenditure. However, several aspects such as obesity, diabetes, Single Nucleotide polymorphisms (SNPs), and oxidative stress affect the normal FAs metabolism and function of FAT/CD36, inducing metabolic disease. Through a comprehensive systematic review of primary studies, this work aimed to document molecular mechanisms related to FAT/CD36 in FAs oxidation and trafficking in skeletal muscle under basal conditions, physical exercise, and diet in healthy individuals.

The Regulation of Fat Metabolism During Aerobic Exercise

Since the lipid profile is altered by physical activity, the study of lipid metabolism is a remarkable element in understanding if and how physical activity affects the health of both professional athletes and sedentary subjects. Although not fully defined, it has become clear that resistance exercise uses fat as an energy source. The fatty acid oxidation rate is the result of the following processes: (a) triglycerides lipolysis, most abundant in fat adipocytes and intramuscular triacylglycerol (IMTG) stores, (b) fatty acid transport from blood plasma to muscle sarcoplasm, (c) availability and hydrolysis rate of intramuscular triglycerides, and (d) transport of fatty acids through the mitochondrial membrane. In this review, we report some studies concerning the relationship between exercise and the aforementioned processes also in light of hormonal controls and molecular regulations within fat and skeletal muscle cells.

Maximum Aerobic Function: Clinical Relevance, Physiological Underpinnings, and Practical Application

The earliest humans relied on large quantities of metabolic energy from the oxidation of fatty acids to develop larger brains and bodies, prevent and reduce disease risk, extend longevity, in addition to other benefits. This was enabled through the consumption of a high fat and low-carbohydrate diet (LCD). Increased fat oxidation also supported daily bouts of prolonged, low-intensity, aerobic-based physical activity. Over the past 40-plus years, a clinical program has been developed to help people manage their lifestyles to promote increased fat oxidation as a means to improve various aspects of health and fitness that include reducing excess body fat, preventing disease, and optimizing human performance. This program is referred to as maximum aerobic function, and includes the practical application of a personalized exercise heart rate (HR) formula of low-to-moderate intensity associated with maximal fat oxidation (MFO), and without the need for laboratory evaluations. The relationship between exercise training at this HR and associated laboratory measures of MFO, health outcomes and athletic performance must be verified scientifically.