ECSS Paris 2023: GSSI
INTRODUCTION: Exogenous carbohydrate oxidation (i.e., from drinks) is reduced in hot conditions (1,2). Increased thermal and cardiovascular strain and reduced gastrointestinal (GI) integrity (3) may impair glucose uptake and transport, gastric emptying, and intestinal absorption. However, dehydration, often resulting from heat exposure, may also contribute to these impairments by reducing blood volume and altering blood flow distribution. As previous studies in hot conditions have not controlled hydration status, the impact of dehydration on reduced exogenous carbohydrate oxidation is unclear. Therefore, this study aimed to investigate the effect of hydration status on exogenous carbohydrate oxidation during running in a hot environment. METHODS: Ten trained male runners (21 ± 2 y; 68.9 ± 7.6 kg; V̇O2peak: 67 ± 6 mL/kg/min) completed a preliminary session (V̇O2peak and sweat rate testing) and two experimental trials [100 min of steady state running at ~65% V̇O2peak in hot conditions (32°C) with hydration (water intake to replace 90% of mass losses; HYD) or to induce dehydration (minimal fluid provided; DEH)]. In each trial, participants consumed 60 g/h (bolus every 20 min) of a 35% dextrose solution enriched with [U-13C] glucose (145 ± 2 δ‰ enrichment). Expired breath (analysed for 13C:12C ratio using GC-IRMS), venous blood samples and subjective scales of GI comfort were collected at rest and every 20 min during exercise. Data were analysed using linear mixed models with significance at P < 0.05. Results presented as mean ± SD. RESULTS: Average (40-100 min) and peak exogenous carbohydrate oxidation rates were 29% (DEH: 0.35 ± 0.15 vs. HYD: 0.50 ± 0.13 g/min; P = 0.016) and 24% (DEH: 0.54 ± 0.19 vs. HYD: 0.71 ± 0.13 g/min; P = 0.017) lower in DEH than HYD, respectively. Total (DEH: 2.52 ± 0.47 vs. HYD: 2.56 ± 0.26 g/min; P = 0.737) and endogenous carbohydrate oxidation (DEH: 2.17 ± 0.36 vs. HYD: 2.06 ± 0.30 g/min; P = 0.188) were not different between trials. GI temperature (DEH: 39.4 ± 0.5°C; HYD: 39.2 ± 0.4°C; P = 0.380) and heart rate (DEH: 173 ± 11 bpm; HYD: 169 ± 12 bpm; P = 0.124) at the end of trials were not different between conditions. Body mass loss (-2.7 ± 0.5% vs. -0.4 ± 0.5%; P < 0.001) and changes in plasma volume from baseline (-9.3 ± 4.1% vs.-2.5 ± 5.1%; P < 0.001) were greater in DEH. No differences in GI symptoms, including stomach bloatedness, were observed between conditions (P > 0.05). CONCLUSION: Prolonged exercise in the heat, with minimal fluid intake leading to dehydration, impaired exogenous carbohydrate oxidation. These findings underscore the importance of hydration and fluid delivery for optimising exogenous carbohydrate utilisation, particularly for athletes aiming to sustain endurance performance in hot conditions. REFERENCES: (1) Jentjens et al. 2002. JAP 92:1562–1572 (2) Reynolds et al. 2025. MSSE Epub ahead of print. (3) Snipe et al. 2018. EJAP 118:389-400
Read CV Loïs MouginECSS Paris 2023: GSSI
INTRODUCTION: Carbohydrates (CHO) are crucial for prolonged moderate- to high-intensity exercise, although storage within the liver and skeletal muscle is relatively limited. The development of practical strategies to optimize glycogen resynthesis with athletes is thereby essential for enhancing recovery and performance. In addition to CHO, protein consumption during recovery supports muscle protein synthesis and enhances muscle glycogen storage, particularly when carbohydrate intake is suboptimal. While protein may aid liver glycogen repletion by promoting hepatic glucose storage and providing glucogenic amino acids, protein stimulates glucagon secretion - potentially impairing liver glycogen synthesis. Therefore, the present study examined the effects of co-ingesting whey protein with dual source carbohydrates on post-exercise liver and muscle glycogen resynthesis. METHODS: Following glycogen-depleting exercise, ten well-trained male cyclists (mean ± SD: age 29 ± 7 years; body mass 78.5 ± 6.4 kg; stature 181.9 ± 4.7 cm; VO2max 57.5 ± 5.8 ml·kg−1·min−1) ingested 60 g.h-1 CHO from either maltodextrin (MAL), fructose (FRU), maltodextrin + fructose (MF) or maltodextrin + fructose plus 30 g whey protein (PRO) at 0 and 180 min during a 5-h recovery period. 13C magnetic resonance spectroscopy and imaging were performed at 0-, 120- and 300-min post-exercise to determine liver and muscle glycogen concentrations and liver volume. RESULTS: Protein co-ingestion resulted in elevated serum insulin and plasma glucagon compared with FRU and MF (P < 0.001 for all). Similarly, serum insulin and plasma glucagon concentrations were markedly higher with MAL when compared with both FRU and MF (P < 0.05 for all), although plasma glucagon concentrations were also higher when compared with PRO (P < 0.001). Liver glycogen concentrations were significantly higher with FRU (276 ± 70 mmol·L-1), MF (257 ± 65 mmol·L-1) and PRO (285 ± 49 mmol·L-1) compared with MAL (198 ± 41 mmol·L-1) (P < 0.05 for all) following 5 hours of recovery. However, muscle glycogen concentrations (MAL, 166 ± 39; FRU, 145 ± 51; MF, 153 ± 39; PRO 154 ± 36, mmol·L-1) were not different between trials (P > 0.05). CONCLUSION: In summary, ingesting dual-source carbohydrates enhances liver glycogen repletion whilst maintaining comparable rates of muscle glycogen resynthesis when compared to maltodextrin only. Notably, despite enhancing glucagonemia, co-ingestion of whey protein (with a 1:1 combination of maltodextrin and fructose) does not compromise post-exercise liver glycogen resynthesis, allowing for increased aminoacidemia alongside rapid glycogen resynthesis. Considering the importance of post-exercise protein intake for muscle reconditioning and the dietary habits of elite endurance athletes, our findings suggest that combining dual-source carbohydrates (a 1:1 ratio of maltodextrin and fructose) with whey protein offers a practical strategy to optimize both amino acid availability and endogenous glycogen resynthesis.
Read CV Sophie HannonECSS Paris 2023: GSSI
INTRODUCTION: Dietary amino acids (AA), such as the essential AA leucine (Leu), are used for building new body proteins (i.e. protein synthesis) or as a source of energy (i.e., oxidation). Our laboratory has developed an oral [13C]Leu ‘breath-test’ that measures the leucine retention (Leu Ret) for protein synthesis as a marker of the body’s ‘anabolic sensitivity’ to dietary AAs. However, the effect of biological sex (i.e., males vs. females) or female hormonal milieu (i.e., naturally cycling eumenorrheic females vs. oral contraceptive (OC) use) on whole-body dietary Leu Ret at rest and following resistance exercise (RE) remains unknown. Thus, the purpose of the study was to determine Leu Ret (i.e., ‘anabolic sensitivity’) in equal groups of n=8 males (26.4±4.8 y, 78.3±7.7 kg body mass (BM), 13.8±5.9% body fat (BF)), eumenorrheic females in the follicular (21.4±3.1 y, 65.1± 0.5 kg BM, 26.4 ± 6.9% BF) and luteal (24.4 ± 4.3 y, 64.7 ± 10.2 kg BM, 28.2±5.1% BF) phases and monophasic OC users (23.3 ± 2.4 y, 59.3±10.0 kg BM, 24.9±4.9% BF) during the active pill phase (days 10-21) upon consuming a [13C]Leu-enriched beverage at rest (FED) and after a bout of full-body RE (EXFED). METHODS: Using a counterbalanced, crossover design, participants ingested a mixed macronutrient beverage containing carbohydrate and crystalline AAs (0.75 and 0.25 g/kg BM, respectively) in both FED and EXFED, enriched to ~5% with [13C]Leu, which is preferentially metabolized in peripheral (e.g. muscle) lean tissues. The oxidation of ingested Leu (Exo Ox) was assessed using 13CO2 enrichment (via isotope ratio mass spectrometry) and CO2 production (via indirect calorimetry) over 6 h. Leu Ret relative to fat-free mass (FFM) was determined by the algebraic difference between total Leu intake and the area-under-the-curve for Exo Ox. RESULTS: Over the 6 h post-prandial period, Leu Ret at rest was greater (p<0.01) in males (16.27 mg/kg FFM) compared to females in the follicular (12.70 mg/kg FFM) but not luteal (14.39 mg/kg FFM) phase or active pill OC users (14.08 mg/kg FFM), with no further group differences (p≥0.05). Although Leu Ret after exercise was ~11.2% greater in males than females in the follicular phase, there were no significant differences between groups (F (3, 28)= 2.65, p= 0.07, f2= 0.39). CONCLUSION: The greater anabolic sensitivity to dietary leucine in males compared to females during the follicular phase at rest is attenuated during recovery from RE. The impact of these differences in whole-body leucine retention on muscle protein metabolism and/or dietary protein requirements at rest or during recovery from RE warrants further investigation. This study is supported by a New Frontiers in Research Fund Grant to D.R.M.
Read CV Nicki PourhashemiECSS Paris 2023: GSSI