ECSS Paris 2023: OP-PN15
INTRODUCTION: Shifts in substrate mobilisation and utilisation occur as exercise intensity increases. Specifically, there is a progressive rise in the relative contribution of carbohydrate oxidation to total energy expenditure, accompanied by a corresponding decline in the relative contribution of fat oxidation. However, from low to moderate exercise intensities, the absolute rate of fat oxidation increases, before declining at higher intensities as carbohydrate becomes the predominant energy substrate. More recently, considerable attention has been directed towards characterising fat oxidation across a wide range of exercise intensities to identify the intensity at which fat oxidation is maximal (MFO). This has been extensively investigated in both healthy and clinical populations. In athletic cohorts, shifts in fat mobilisation and utilisation are critical for endurance performance. Notably, most studies have assessed MFO under ‘fresh’ conditions, largely neglecting the potential influence of prior exercise. Accordingly, the purpose of the present study was to examine the effects of preceding heavy-intensity exercise on maximal fat oxidation in well-trained endurance cyclists. METHODS: Twenty-five well-trained male cyclists (age: 22 ± 4 years; V̇O₂peak: 64.0 ± 5.3 mL·kg⁻¹·min⁻¹) were recruited for this study. Participants attended the laboratory on two separate occasions. On Day 1 (fresh, non-fatigued condition), they performed a ramp-incremental exercise test on an electronically braked cycle ergometer. On Day 2, participants returned to complete a second ramp-incremental test following 90 min of continuous cycling performed at 110% of the gas exchange threshold. Whole-body fat oxidation rates were determined using indirect calorimetry and expressed as a function of exercise intensity during both ramp-incremental tests. RESULTS: MFO was significantly greater during the fatigued ramp-incremental exercise test following prolonged heavy-intensity exercise compared with the fresh, unfatigued condition (1.12 ± 0.20 vs. 0.79 ± 0.12 g·min⁻¹, P < 0.05). Similarly, Fatmax (i.e., the exercise intensity corresponding to MFO) occurred at a higher relative intensity in the fatigued condition compared with the fresh condition (P < 0.05). The Fatmax zone (i.e., defined as the range of exercise intensities eliciting fat oxidation rates within 10% of MFO) differed between conditions (P < 0.05). In the fresh test, the Fatmax zone ranged from 41.1 ± 6.7 to 67.3 ± 4.0% HRmax, whereas in the fatigued state it ranged from 43.7 ± 7.5 to 74.0 ± 6.3% HRmax (P < 0.05). The relative contribution of fat to total energy expenditure was lower in the fresh condition (55.8 ± 16.4%) compared with the fatigued condition (75.1 ± 14.9%) (P < 0.05). CONCLUSION: These findings demonstrate that maximal fat oxidation and its derived indices are influenced by prior heavy-intensity exercise in well-trained endurance cyclists, with important practical and theoretical implications.
Read CV Andrea Gomes BernardesECSS Paris 2023: OP-PN15
INTRODUCTION: Both the timing of exercise and the duration of pre-exercise fasting influence metabolic responses and energy balance. However, the combined effects of these factors on post-exercise energy intake and appetite regulation remain poorly defined. This study examined the independent and interactive effects of time of day and fasting duration on acute and 24 h post-exercise energy intake, subjective appetite, and substrate oxidation. METHODS: In a randomized five-condition crossover design, 35 healthy young adults completed three fasted exercise trials consisting of 30 min treadmill running at 65 percent of peak oxygen uptake: morning exercise following a 12 h overnight fast, evening exercise following a 6 h fast, and evening exercise following a 12 h fast. A subsample (n = 17) additionally completed fed morning and fed evening exercise sessions. Acute post-exercise energy intake was assessed using an ad libitum meal, while total energy intake over the subsequent 24 h was measured via weighed food records. Subjective appetite ratings were obtained before and after exercise, and substrate oxidation during exercise was determined by indirect calorimetry. Linear mixed models were applied for statistical analyses. RESULTS: Acute post-exercise energy intake differed significantly across fasted conditions, increasing from morning to evening exercise and being highest following evening exercise after a 12 h fast (p < 0.001). Total 24 h energy intake showed a similar pattern, with the greatest intake observed after evening exercise following prolonged fasting (p < 0.001). Hunger, desire to eat, and prospective food consumption were consistently higher, and fullness lower, after evening compared with morning exercise, paralleling intake responses. Substrate oxidation during exercise was strongly influenced by condition, with greater fat oxidation during fasted and evening exercise (p < 0.001). In the subsample, pre-exercise feeding altered substrate oxidation but did not attenuate acute or 24 h post-exercise energy intake or appetite responses. CONCLUSION: Prolonged fasting combined with evening exercise resulted in consistently greater compensatory energy intake, evident both at the post-exercise meal and across the subsequent 24 h, indicating a sustained rather than transient response. Although fasting and feeding altered substrate oxidation during exercise markedly, these metabolic shifts were not accompanied by corresponding reductions in post-exercise intake, supporting a dissociation between substrate use and behavioral energy compensation. Collectively, these findings indicate that temporal context and fasting-related factors play a dominant role in post-exercise appetite regulation, outweighing acute metabolic signals.
Read CV Karsten KoehlerECSS Paris 2023: OP-PN15
INTRODUCTION: The common R577X polymorphism within ACTN3 gene renders ~20% of the global human population α-actinin-3 deficient. Because of its effects on skeletal muscle properties such as muscle mass and fiber composition, this genetic variation may also influence whole-body metabolism and thereby modify health and well-being. The objective of the current study was to compare body composition and metabolic health markers between overweight α-actinin-3-deficient (XX) and α-actinin-3-expressing (RR) individuals. METHODS: Untrained overweight participants (Men: RR n=20, XX n=20; Women: RR n=21, XX n=19; 43 ± 7 years; BMI 29 ± 3 kg/m2) underwent assessments of segmental body composition and bone mineral content (DXA), m. vastus lateralis thickness (ultrasound), resting metabolism, C-reactive protein, blood lipid profile, glucose tolerance and insulin sensitivity. Data were analyzed using two-way repeated or factorial ANOVA. RESULTS: Anthropometrical and body composition features, including body mass, fat %, visceral adipose tissue mass, bone mineral content and vastus lateralis thickness, did not differ between the genotype groups in either women or men. However, individuals with the XX genotype had lower fat-free mass compared with RR individuals, irrespective of sex (genotype effect: p=0.035). There were no differences between the genotype groups in measured resting metabolic rate and fat oxidation rate, blood lipid profile, C-reactive protein level or glucose tolerance. However, women of the XX genotype had a smaller insulin response to the oral glucose tolerance test compared to RR women (genotype effect: p=0.042), while there was no difference in insulin response between RR and XX men. CONCLUSION: In conclusion, our results show no major effect of ACTN3 R577X polymorphism on metabolic health and body composition in untrained overweight but otherwise healthy men and women. Nevertheless, a smaller total and lean body mass together with less insulin required to handle a constant glucose load in XX than in RR women is intriguing and calls for further investigation of ACTN3 effects on carbohydrate metabolism.
Read CV Tomas VenckunasECSS Paris 2023: OP-PN15