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