ECSS Paris 2023: CP-PN17
INTRODUCTION: Morning high-intensity interval training (HIIT) sessions are often performed after an overnight fast, yet there is conflicting evidence on whether pre-exercise carbohydrate feeding improves HIIT performance, substrate utilisation and perceptions of effort. Existing studies are limited by open-label designs, narrow exercise tasks and inadequate expectancy control. This study examined whether a carbohydrate breakfast alters HIIT performance, acute physiological responses, and perceived exertion using an ecologically valid, expectancy-controlled protocol. METHODS: Twenty-seven trained male participants (age: 23 ± 3 years; VO2peak: 54.2 ± 5.5 mL/kg/min) with endurance or team-sport backgrounds completed two main trials in a randomised, double-blind, crossover design. After an overnight fast, participants consumed an individualised semi-solid breakfast 90 min pre-exercise in each main trial: carbohydrate (maltodextrin 1.5 g/kg; 600 mL) or a visually identical non-caloric placebo. The main trial comprised six 4-min treadmill intervals separated by 2 min of low-intensity jogging. Intervals 1-3 were performed at 85% vVO2peak. Intervals 4-6 began at 85% vVO2peak and then became self-paced, with participants encouraged to maximise distance covered. Total distance across intervals 4-6 was the primary performance outcome. Gas exchange, rating of perceived exertion (RPE), blood lactate and blood glucose, and post-session perceptions were assessed. Outcomes were analysed using paired t-tests and 2-way repeated-measures ANOVA. RESULTS: Total distance covered in intervals 4-6 was numerically greater after the carbohydrate breakfast than after placebo (2658 ± 324 vs 2622 ± 311 m), but this difference was not statistically significant (p = 0.115, Cohen's d = 0.31). During intervals 1-3, carbohydrate increased the respiratory exchange ratio (RER) and carbohydrate oxidation (CHOox) and reduced fat oxidation (Fatox) versus placebo (condition main effects, all p < 0.001). Resting blood lactate and blood glucose did not differ by condition (p = 0.801 and p = 0.848). Across intervals, blood lactate and blood glucose increased (both p < 0.001) without significant condition effects (p = 0.341 and p = 0.070), and RPE increased across intervals (p < 0.001) with no condition effect (p = 0.236). Sessional RPE, enjoyment, and likelihood to repeat did not differ between conditions. CONCLUSION: A carbohydrate-rich breakfast consumed 90 minutes before morning HIIT significantly altered substrate utilisation, shifting metabolism towards greater CHOox and reduced Fatox, but did not produce statistically significant improvements in HIIT performance or perceived exertion compared with an energy-free placebo. These findings suggest that, during an approximately 30-min morning HIIT session after an overnight fast, pre-exercise carbohydrate intake altered substrate utilisation without a clear improvement in brief HIIT performance.
Read CV Weilin MaoECSS Paris 2023: CP-PN17
INTRODUCTION: MCT2 and MCT4 mediate complementary lactate uptake and efflux during high-intensity exercise. The MCT2 rs3763980 TA and MCT4 rs11323780 TT genotype combination has been associated with lower maximal post-exercise blood lactate concentration (Maculewicz et al. 2025). Lactate acts as a signalling molecule promoting muscle fibre-type remodelling toward more oxidative phenotypes (Zhou et al. 2024). Consequently, individual differences in lactate metabolism attributable to genetic traits may affect weightlifting performance, which requires a high explosive force relative to the body mass. This study examined the association between MCT2 rs3763980 and MCT4 rs11323780 polymorphisms with weightlifting performance in elite athletes. METHODS: A total of 215 elite weightlifters (121 men, 94 women) and 306 controls (143 men, 163 women) were recruited. Genomic DNA was extracted from saliva using an Oragene DNA kit. Genotyping of MCT2 rs3763980 (MCT2) and MCT4 rs1055013 (MCT4) polymorphisms was performed using TaqMan probe assays (WL) and the Japonica Array® v2 (CON). Rs1055013 is in complete linkage disequilibrium with rs11323780 (r² = 1.0). Weightlifting performance was assessed by converting the combined total of self-reported best records in the clean, jerk, and snatch movements into Wilks’ points adjusted for body mass and sex. Hardy–Weinberg equilibrium (HWE) and genotype frequencies were compared using the chi-square test. In the WL group, performance was compared between the MCT2 TA + MCT4 T allele group and the other genotypes using a one-way ANOVA. RESULTS: All examined polymorphisms were in HWE in the CON. No significant differences in genotype frequencies were observed between groups for either MCT2 (p = 0.60) or MCT4 (p = 0.30) genotype. The frequency of the MCT2 TA + MCT4 T allele (TA+TT) combination was 39.5% in the WL and 42.8% in the CON, with no significant difference between groups (p = 0.46). Among WL, those with the TA+T allele combination showed significantly higher combined performance than those with other genotypes (196.9 ± 29.8 vs. 188.4 ± 24.1, p = 0.027). CONCLUSION: The MCT2 rs3763980 TA genotype and MCT4 rs1055013 T allele combination was associated with superior weightlifting performance among elite athletes, although genotype frequencies did not differ between WL controls. Future studies should examine the effects of MCT2 and MCT4 polymorphisms on skeletal muscle characteristics, such as muscle fibre composition, to clarify the mechanisms underlying the association between these genetic variants and performance. Maculewicz et al. 2025. 'The interactions between monocarboxylate transporter genes MCT1, MCT2, and MCT4 and the kinetics of blood lactate production and removal after high-intensity efforts in elite males: a cross-sectional study', BMC Genomics, 26: 133. Zhou et al. 2024. 'Lactate-induced metabolic remodeling and myofiber type transitions via activation of the Ca(2+)-NFATC1 signaling pathway', J Cell Physiol, 239: e31290.
Read CV Mika Kamiya-SaitoECSS Paris 2023: CP-PN17
INTRODUCTION: Human physiology is regulated by an endogenous timing system that helps coordinate environmental cues and physiological/metabolic processes. Previous research has primarily focused on the effects of light, sleep and nutrition as synchronisers of this timing system. In contrast, the effects of physical activity and exercise have received comparatively little research attention. METHODS: In this interim analysis, twelve participants (7 males and 5 females) completed a 37-hour laboratory protocol after adhering to a 1-week of period of standardised sleep-wake timing and light exposure. Participants were randomly assigned to one of three conditions - either continuous rest (CONTROL), morning exercise (EARLY) or evening exercise (LATE). Specifically, following a familiarisation night in the laboratory, the CONTROL group rested for 24 hours (measures starting at 0800 h), whereas the EARLY and LATE groups performed 60-minutes of moderate-vigorous intensity cycling (50 % delta of LT1 and LT2) at either 0800 h or 2000 h, respectively, then rested for the subsequent 23 hours of measurement. All groups received continuous feeding via nasogastric tube for 24 h, prescribed in quantities to meet individual metabolic requirements (as established by indirect calorimetry). In the LATE condition, continuous nutrient delivery commenced at 2000 h, from onset of exercise and continued during the nighttime and following day. In contrast, in the EARLY and CONTROL conditions, continuous feeding began at 0800 h, coinciding with the onset of exercise in the EARLY condition and continued throughout the daytime and nighttime. Substrate oxidation was calculated hourly from indirect calorimetry throughout the wake period, alongside aural temperature every hour during the light phase (0700-2200 h) and every 4 hours during the dark phase (2200-0700 h), with blood pressure measured hourly during waking hours. A repeated measures ANOVA (condition x time) was used to explore patterns within and between experimental conditions. RESULTS: Lipid oxidation was significantly higher in the LATE exercise condition compared to EARLY and CONTROL (main effect of condition (p=0.031) but no such differences were evident for carbohydrate oxidation, aural temperature nor blood pressure between groups. Mean ± SD lipid oxidation rates were 0.066 ± 0.023 g·min-1 (CONTROL), 0.066 ± 0.025 g·min-1 (EARLY), and 0.102 ± 0.011 g·min-1 (LATE). CONCLUSION: The greater rates of lipid oxidation observed in the LATE condition were especially apparent during the morning after, and may be attributable to a direct effect of having exercised the previous evening (rather than immediately beforehand) and/or due to the differences in feeding pattern relative to daytime measurements that are inherent to this protocol (i.e. continuous delivery of nutrients following exercise during the nighttime as opposed to the daytime).
Read CV Katie HutchinsECSS Paris 2023: CP-PN17