Effects of glycemic index meal and CHO-electrolyte drink on cytokine response and run performance in endurance athletes

Effects of pre-exercise high and low glycaemic index meals on substrate metabolism and appetite in middle-aged women

Few studies have examined the influence of pre-exercise meals with different glycaemic indices (GIs) on substrate oxidation and non-homeostatic appetite (i.e. food reward) in adults of various ages and ethnicities. We aimed to examine the effects of pre-exercise high and low GI meals on substrate oxidation and food reward in middle-aged Japanese women. This randomised crossover trial included fifteen middle-aged women (aged 40⋅9 ± 6⋅5 years, mean ± sd). The participants consumed a high or low GI breakfast at 09.00 and rested until 11.00. Thereafter, participants performed a 60-min walk at 50 % of their estimated maximum oxygen uptake (11.00-12.00) and rested until 13.00. Expired gas samples were collected every 30 min prior to walking, and samples were collected continuously throughout the walking and post-walking periods. Blood samples and subjective appetite ratings were collected every 30 min, except during walking. The Leeds Food Preference Questionnaire in Japanese (LFPQ-J) was used to assess food reward at 09.00, 10.00, and 13.00 h. The cumulative fat oxidation during exercise was higher in the low GI trial than in the high GI trial (P = 0⋅03). The cumulative carbohydrate oxidation during walking was lower in the low GI trial than in the high GI trial (P = 0⋅01). Trial-by-time interactions were not found for any food-reward parameters between trials. Low GI meals elicited enhanced fat oxidation during a subsequent 60-min walk in middle-aged women. However, meals with different GIs did not affect food reward evaluated over time in the present study.

Carbohydrates and Endurance Exercise: A Narrative Review of a Food First Approach

Carbohydrate (CHO) supplements such as bars, gels, drinks and powders have become ubiquitous as effective evidence-based CHO sources that improve endurance exercise performance. However, athletes are increasingly turning to more cost-effective ‘food-first’ approaches for CHO ingestion to improve exercise performance. Mixed CHO foods including cooked lentils, oats, honey, raisins, rice, and potatoes are all effective pre-exercise CHO food sources. Caution is advised when selecting some of these foods as a primary CHO source, as some athletes may be prone to gastrointestinal discomfort—especially regarding those foods where the quantities required for recommended CHO intake may be voluminous (e.g., potatoes). Palatability may be another barrier to the ingestion of some of these CHO-rich foods. Although most of these CHO-rich foods appear effective for exercise performance or recovery when consumed pre- and post-exercise, not all are viable to ingest during exercise due to difficulties in the quantities required, transport, and/or gastrointestinal discomfort. Raisins, bananas and honey may be particularly useful CHO foods for consumption during exercise, as they are easily transportable. Athletes should trial CHO food sources before, during and/or following training before implementation during competition.

Pre-exercise Carbohydrate Drink Adding Protein Improves Post-exercise Fatigue Recovery

Purpose: This study aimed to assess the requirement of protein in pre-exercise carbohydrate drinks for optimal endurance performance at high intensity and post-exercise fatigue recovery.

Methods: Endurance performance at 85% V.⁢O2_peak of young men (age 20 ± 0.9 years, V.⁢_2peak 49.3 ± 0.3 L/min) was measured for two consecutive days using cycling time to exhaustion and total work exerted 2 h after three isocaloric supplementations: RICE (50 g, protein: 1.8 g), n = 7; SOY + RICE (50 g, protein: 4.8 g), n = 7; and WHEY + RICE (50 g, protein: 9.2 g), n = 7.

Results: Endurance performance was similar for the three supplemented conditions. Nevertheless, maximal cycling time and total exerted work from Day 1 to Day 2 were improved in the WHEY + RICE (+21%, p = 0.05) and SOY-RICE (+16%, p = 0.10) supplemented conditions, not the RICE supplemented condition. Increases in plasma interleukin-6 (IL-6) were observed 1 h after exercise regardless of supplemented conditions. Plasma creatine kinase remained unchanged after exercise for all three supplemented conditions. Increases in ferric reducing antioxidant power (FRAP) after exercise were small and similar for the three supplemented conditions.

Conclusion: Adding protein into carbohydrate drinks provides no immediate benefit in endurance performance and antioxidant capacity yet enhances fatigue recovery for the next day. Soy-containing carbohydrate drink, despite 50% less protein content, shows similar fatigue recovery efficacy to the whey protein-containing carbohydrate drink. These results suggest the importance of dietary nitrogen sources in fatigue recovery after exercise.

Pre-Sleep Low Glycemic Index Modified Starch Does Not Improve Next-Morning Fuel Selection or Running Performance in Male and Female Endurance Athletes

To determine the effects of pre-sleep supplementation with a novel low glycemic index (LGI) carbohydrate (CHO) on next-morning substrate utilization, gastrointestinal distress (GID), and endurance running performance (5-km time-trial, TT). Using a double-blind, randomized, placebo (PLA) controlled, crossover design, trained participants (n = 14; 28 ± 9 years, 8/6 male/female, 55 ± 7 mL/kg/min) consumed a LGI, high glycemic index (HGI), or 0 kcal PLA supplement ≥ 2 h after their last meal and <30 min prior to sleep. Upon arrival, resting energy expenditure (REE), substrate utilization, blood glucose, satiety, and GID were assessed. An incremental exercise test (IET) was performed at 55, 65, and 75% peak volume of oxygen consumption (VO_2peak) with GID, rating of perceived exertion (RPE) and substrate utilization recorded each stage. Finally, participants completed the 5-km TT. There were no differences in any baseline measure. During IET, CHO utilization tended to be greater with LGI (PLA, 56 ± 11; HGI, 60 ± 14; LGI, 63 ± 14%, p = 0.16, η² = 0.14). GID was unaffected by supplementation at any point (p > 0.05). Performance was also unaffected by supplement (PLA, 21.6 ± 9.5; HGI, 23.0 ± 7.8; LGI, 24.1 ± 4.5 min, p = 0.94, η² = 0.01). Pre-sleep CHO supplementation did not affect next-morning resting metabolism, BG, GID, or 5-km TT performance. The trend towards higher CHO utilization during IET after pre-sleep LGI, suggests that such supplementation increases morning CHO availability.

The effects of a pre-exercise meal on postexercise metabolism following a session of sprint interval training

Sprint interval training (SIT) has demonstrated reductions in fat mass through potential alterations in postexercise metabolism. This study examined whether exercising in the fasted or fed state affects postexercise metabolism following acute SIT. Ten active males performed a bout of modified SIT (8 × 15-s sprints; 120 s recovery) in both a fasted (FAST) and fed (FED) state. Gas exchange was collected through 3 h postexercise, appetite perceptions were measured using a visual analog scale, and energy intake was recorded using dietary food logs. There was no difference in energy expenditure between conditions at any time point (p > 0.329) or in total session energy expenditure (FED: 514.8 ± 54.9 kcal, FAST: 504.0 ± 74.3 kcal; p = 0.982). Fat oxidation at 3 h after exercise was higher in FED (0.110 ± 0.04 g·min^-1) versus FAST (0.069 ± 0.02 g·min^-1; p = 0.013) though not different between conditions across time (p > 0.340) or in total postexercise fat oxidation (FED: 0.125 ± 0.04 g·min^-1, FAST: 0.105 ± 0.02 g·min^-1; p = 0.154). Appetite perceptions were lower in FED (-4815.0 ± 4098.7 mm) versus FAST (-707.5 ± 2010.4 mm, p = 0.022); however, energy intake did not differ between conditions (p = 0.429). These results demonstrate the fasted or fed state does not augment postexercise metabolism following acute SIT in a way that would favour fat loss following training. Novelty Energy expenditure was similar between conditions, while fat oxidation was significantly greater in FED at 3 h after exercise. Appetite perceptions were significantly lower in FED; however, energy intake was not different between conditions. Current findings suggest that performing SIT in the fed or fasted state would not affect fat loss following training.

Effect of Glycemic Index of a Pre-exercise Meal on Endurance Exercise Performance: A Systematic Review and Meta-analysis

BACKGROUND

Low glycemic index (GI) pre-exercise meals may enhance endurance performance by maintaining euglycemia and altering fuel utilization. However, evidence for performance benefits is equivocal.

OBJECTIVE

To evaluate the effect of a low GI (LGI) versus a high GI (HGI) pre-exercise meal on endurance performance using meta-analyses.

METHODS

Data sources included MEDLINE, SPORTDiscus, AUSPORT, AusportMed, Web of Science, and Scopus. Eligibility criteria were randomized, crossover trials with an endurance exercise (≥60 min) component, e.g., time trial (TT), time to exhaustion (TTE) test, or submaximal bout followed by TT or TTE. Participants were healthy, active individuals aged ≥16 years. Interventions included a LGI (≤55) and HGI (≥70) meal ingested 30-240 min before exercise. Study quality was assessed using an adapted version of the validated Downs and Black tool. Effect size (ES) and 95 % confidence interval were calculated for each study and pooled according to performance test type and whether exogenous carbohydrate (CHO) was given during exercise. Potential effect modifiers including exercise duration, pre-exercise meal timing, glycemic load (GL), and fitness were assessed using meta-regression.

RESULTS

The search netted 3431 citations with 19 studies eligible for inclusion (totaling 188 participants; 91 % male; VO_2max: >50 ml/kg/min). Meals with 0.18-2 g CHO/kg body mass, and a mean GI and glycemic load of 82 (GL: 72) and 35 (GL: 32) for HGI and LGI, respectively, were given between 30 and 210 min before exercise. All test types without CHO ingestion during exercise showed slightly improved performance with LGI, but no significant pooled effects were observed (ES: -0.17 to -0.36; p > 0.05). Studies where exogenous CHO was ingested during exercise showed conflicting results (ES: -0.67 to 0.11; p = 0.04 to 0.94). No significant relationship was observed with any of the effect modifiers (p > 0.05). No consistent metabolic responses (glucose, insulin, lactate, respiratory exchange ratio) during exercise were observed with either meal type.

LIMITATIONS

There were small numbers of studies within each exercise testing protocol and limited statistical power within studies. Pre-exercise meal timing, GL, meal composition and participant fitness varied across studies, limiting the capacity to assess the influence of these factors on study outcomes.

CONCLUSION

There was no clear benefit of consuming a LGI pre-exercise meal for endurance performance regardless of carbohydrate ingestion during exercise.

Nighttime feeding likely alters morning metabolism but not exercise performance in female athletes

The timing of morning endurance competition may limit proper pre-race fueling and resulting performance. A nighttime, pre-sleep nutritional strategy could be an alternative method to target the metabolic and hydrating needs of the early morning athlete without compromising sleep or gastrointestinal comfort during exercise. Therefore, the purpose of this investigation was to examine the acute effects of pre-sleep chocolate milk (CM) ingestion on next-morning running performance, metabolism, and hydration status. Twelve competitive female runners and triathletes (age, 30 ± 7 years; peak oxygen consumption, 53 ± 4 mL·kg(-1)·min(-1)) randomly ingested either pre-sleep CM or non-nutritive placebo (PL) ∼30 min before sleep and 7-9 h before a morning exercise trial. Resting metabolic rate (RMR) was assessed prior to exercise. The exercise trial included a warm-up, three 5-min incremental workloads at 55%, 65%, and 75% peak oxygen consumption, and a 10-km treadmill time trial (TT). Physiological responses were assessed prior, during (incremental and TT), and postexercise. Paired t tests and magnitude-based inferences were used to determine treatment differences. TT performances were not different ("most likely trivial" improvement with CM) between conditions (PL: 52.8 ± 8.4 min vs CM: 52.8 ± 8.0 min). RMR was "likely" increased (4.8%) and total carbohydrate oxidation (g·min(-1)) during exercise was "possibly" or likely increased (18.8%, 10.1%, 9.1% for stage 1-3, respectively) with CM versus PL. There were no consistent changes to hydration indices. In conclusion, pre-sleep CM may alter next-morning resting and exercise metabolism to favor carbohydrate oxidation, but effects did not translate to 10-km running performance improvements.

Metabolic response to different glycemic indexes of pre-exercise meal

INTRODUCTION: To ensure performance and health, the type of food and the time of pre-exercise ingestion should be considered by practitioners of morning physical activity. Objective: This study assessed the metabolic response after pre-exercise meals with different glycemic indexes (GI) and in the fasting state adopting different types of hydration.METHODS: Twelve men performed four experimental tests; two with pre-exercise meals of high GI (HGI) and low GI (LGI), and two were performed in the fasting state with hydration: water (H2O) and carbohydrate drink (CHO). Each test consisted of a pre-exercise rest period of 30 minutes followed by 60 minutes of cycle ergometer with continuous load equivalent to 60% of the extrapolated maximal oxygen consumption (VO2MaxExt). During the exercise, participants were hydrated every 15 minutes with 3mL per kg body weight. During each experimental test, venous blood samples were obtained for fasting and at 15-minute intervals during rest, and every 20 minutes during exercise. The gas analysis was carried out in periods of 5 minutes every 20 minutes of exercise.RESULTS: There was no difference in substrate oxidation. After 20 minutes of exercise, pre-exercise food intake procedures showed similar behavior, having only reduced blood glucose levels compared to fasting procedures (p<0.01). There was maintenance of blood glucose at stable and higher levels during exercise in relation to the other tests in the fast procedure with CHO.CONCLUSION: The data suggest that despite the similar metabolic behavior between LGI and HGI meals, the adoption of a LGI meal before the morning exercise seems to be a more suitable feeding practice due to higher tendency of rebound hypoglycemia after HGI meal and when morning exercise is performed on fasting, hydration with CHO seems to minimize the hypoglycemic risk arising from that state.

Performance effects and metabolic consequences of caffeine and caffeinated energy drink consumption on glucose disposal

This review documents two opposing effects of caffeine and caffeine-containing energy drinks, i.e., their positive effects on athletic performance and their negative impacts on glucose tolerance in the sedentary state. Analysis of studies examining caffeine administration prior to performance-based exercise showed caffeine improved completion time by 3.6%. Similar analyses following consumption of caffeine-containing energy drinks yielded positive, but more varied, benefits, which were likely due to the diverse nature of the studies performed, the highly variable composition of the beverages consumed, and the range of caffeine doses administered. Conversely, analyses of studies administering caffeine prior to either an oral glucose tolerance test or insulin clamp showed a decline in whole-body glucose disposal of ~30%. The consequences of this resistance are unknown, but there may be implications for the development of a number of chronic diseases. Both caffeine-induced performance enhancement and insulin resistance converge with the primary actions of caffeine on skeletal muscle.

Pre-exercise nutrition: the role of macronutrients, modified starches and supplements on metabolism and endurance performance

Endurance athletes rarely compete in the fasted state, as this may compromise fuel stores. Thus, the timing and composition of the pre-exercise meal is a significant consideration for optimizing metabolism and subsequent endurance performance. Carbohydrate feedings prior to endurance exercise are common and have generally been shown to enhance performance, despite increasing insulin levels and reducing fat oxidation. These metabolic effects may be attenuated by consuming low glycemic index carbohydrates and/or modified starches before exercise. High fat meals seem to have beneficial metabolic effects (e.g., increasing fat oxidation and possibly sparing muscle glycogen). However, these effects do not necessarily translate into enhanced performance. Relatively little research has examined the effects of a pre-exercise high protein meal on subsequent performance, but there is some evidence to suggest enhanced pre-exercise glycogen synthesis and benefits to metabolism during exercise. Finally, various supplements (i.e., caffeine and beetroot juice) also warrant possible inclusion into pre-race nutrition for endurance athletes. Ultimately, further research is needed to optimize pre-exercise nutritional strategies for endurance performance.

Índice glicêmico da refeição pré-exercício e metabolismo da glicose na atividade aeróbica

O índice glicêmico (IG) é um indicador funcional que pode ser usado para classificar carboidratos de acordo com sua resposta glicêmica e insulinêmica em relação a um alimento conhecido, pão branco ou glicose. No ramo da nutrição esportiva, este é considerado principalmente para compor a refeição pré-exercício, pois afeta diretamente a resposta glicêmica pós-prandial, e dependendo de alguns fatores, tais como o tempo prévio de ingestão, existe o risco de hipoglicemia de rebote durante o exercício. Elucidar, atraves de uma revisão sistematizada, qual estratégia nutricional é a mais adequada empregando refeições de diferentes índices glicêmicos pré-exercício. Foi consultada a base de dados PubMed, utilizando os descritores: aerobic exercise, glicemic index e glycemia, de forma combinada. Foram adotados como critérios de inclusão artigos originais, publicados em inglês nos últimos cinco anos e realizados com humanos, e como critério de exclusão, amostra não saudável e exercício sem predominância aeróbica. Foram selecionados 11 artigos, os quais variavam quanto ao gênero da amostra e seu condicionamento, o tipo de exercício selecionado, assim como sua duração e intensidade, o valor de IG adotado, e o tempo prévio de ingestão alimentar, de 15 minutos a três horas. Pela recorrência de alguns resultados, alimentos de baixo índice glicêmico causam menor alteração glicêmica pós-prandial, o que pode acarretar em um comportamento mais estável ao longo do exercício, tornando-se uma estratégia nutricional mais conservadora para a população em geral.

Carbohydrate supplementation and prolonged intermittent high-intensity exercise in adolescents: research findings, ethical issues and suggestions for the future

In the last decade, research has begun to investigate the efficacy of carbohydrate supplementation for improving aspects of physical capacity and skill performance during sport-specific exercise in adolescent team games players. This research remains in its infancy, and further study would be beneficial considering the large youth population actively involved in team games. Literature on the influence of carbohydrate supplementation on skill performance is scarce, limited to shooting accuracy in adolescent basketball players and conflicting in its findings. Between-study differences in the exercise protocol, volume of fluid and carbohydrate consumed, use of prior fatiguing exercise and timing of skill tests may contribute to the different findings. Conversely, initial data supports carbohydrate supplementation in solution and gel form for improving intermittent endurance running capacity following soccer-specific shuttle running. These studies produced reliable data, but were subject to limitations including lack of quantification of the metabolic response of participants, limited generalization of data due to narrow participant age and maturation ranges, use of males and females within the same sample and non-standardized pre-exercise nutritional status between participants. There is a lack of consensus regarding the influence of frequently consuming carbohydrate-containing products on tooth enamel erosion and the development of obesity or being overweight in adolescent athletes and non-athletes. These discrepancies mean that the initiation or exacerbation of health issues due to frequent consumption of carbohydrate-containing products by adolescents cannot be conclusively refuted. Coupled with the knowledge that consuming a natural, high-carbohydrate diet -3-8 hours before exercise can significantly alter substrate use and improve exercise performance in adults, a moral and ethical concern is raised regarding the direction of future research in order to further knowledge while safeguarding the health and well-being of young participants. It could be deemed unethical to continue study into carbohydrate supplementation while ignoring the potential health concerns and the possibility of generating similar performance enhancements using natural dietary interventions. Therefore, future work should investigate the influence of pre-exercise dietary intake on the prolonged intermittent, high-intensity exercise performance of adolescents. This would enable quantification of whether pre-exercise nutrition can modulate exercise performance and, if so, the optimum dietary composition to achieve this. Research could then combine this knowledge with ingestion of carbohydrate-containing products during exercise to facilitate ethical and healthy nutritional guidelines for enhancing the exercise performance of adolescents. This article addresses the available evidence regarding carbohydrate supplementation and prolonged intermittent, high-intensity exercise in adolescent team games players. It discusses the potential health concerns associated with the frequent use of carbohydrate-containing products by adolescents and how this affects the research ethics of the field, and considers directions for future work.

Exercise-induced immunodepression in endurance athletes and nutritional intervention with carbohydrate, protein and fat-what is possible, what is not?

Heavily exercising endurance athletes experience extreme physiologic stress, which is associated with temporary immunodepression and higher risk of infection, particularly upper respiratory tract infections (URTI). The aim of this review is to provide a critical up-to-date review of existing evidence on the immunomodulatory potential of selected macronutrients and to evaluate their efficacy. The results of 66 placebo-controlled and/or crossover trials were compared and analysed. Among macronutrients, the most effective approach to maintain immune function in athletes is to consume ≥6% carbohydrate during prolonged exercise. Because inadequate nutrition affects almost all aspects of the immune system, a well-balanced diet is also important. Evidence of beneficial effects from other macronutrients is scarce and results are often inconsistent. Using a single nutrient may not be as effective as a mixture of several nutritional supplements. Due to limited research evidence, with the exception of carbohydrate, no explicit recommendations to reduce post-exercise URTI symptoms with single macronutrients can be derived.

New perspectives on nutritional interventions to augment lipid utilisation during exercise

The enhancement of fat oxidation during exercise is an aim for both recreational exercising individuals and endurance athletes. Nutritional status may explain a large part of the variation in maximal rates of fat oxidation during exercise. This review reveals novel insights into nutritional manipulation of substrate selection during exercise, explaining putative mechanisms of action and evaluating the current evidence. Lowering the glycaemic index of the pre-exercise meal can enhance lipid utilisation by up to 100 % through reduced insulin concentrations, although its application may be restricted to specific training sessions rather than competition. Chronic effects of dietary glycaemic index are less clear and warrant future study before firm recommendations can be made. A flurry of recent advances has overthrown the conventional view of l-carnitine supplementation, with skeletal muscle uptake possible under certain dietary conditions and providing a strategy to influence energy metabolism in an exercise intensity-dependent manner. Use of non-carbohydrate nutrients to stimulate muscle l-carnitine uptake may prove more beneficial for optimising lipid utilisation, but this requires more research. Studies investigating fish oil supplementation on fat oxidation during exercise are conflicting. In spite of some strong putative mechanisms, the only crossover trial showed no significant effect on lipid use during exercise. Ca may increase NEFA availability although it is not clear whether these effects occur. Ca and caffeine can increase NEFA availability under certain circumstances which could theoretically enhance fat oxidation, yet strong experimental evidence for this effect during exercise is lacking. Co-administration of nutrients to maximise their effectiveness needs further investigation.

Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation

There is a growing body of research on the influence of ingesting carbohydrate-electrolyte solutions immediately prior to and during prolonged intermittent, high-intensity exercise (team games exercise) designed to replicate field-based team games. This review presents the current body of knowledge in this area, and identifies avenues of further research. Almost all early work supported the ingestion of carbohydrate-electrolyte solutions during prolonged intermittent exercise, but was subject to methodological limitations. A key concern was the use of exercise protocols characterized by prolonged periods at the same exercise intensity, the lack of maximal- or high-intensity work components and long periods of seated recovery, which failed to replicate the activity pattern or physiological demand of team games exercise. The advent of protocols specifically designed to replicate the demands of field-based team games enabled a more externally valid assessment of the influence of carbohydrate ingestion during this form of exercise. Once again, the research overwhelmingly supports carbohydrate ingestion immediately prior to and during team games exercise for improving time to exhaustion during intermittent running. While the external validity of exhaustive exercise at fixed prescribed intensities as an assessment of exercise capacity during team games may appear questionable, these assessments should perhaps not be viewed as exhaustive exercise tests per se, but as indicators of the ability to maintain high-intensity exercise, which is a recognized marker of performance and fatigue during field-based team games. Possible mechanisms of exercise capacity enhancement include sparing of muscle glycogen, glycogen resynthesis during low-intensity exercise periods and attenuated effort perception during exercise. Most research fails to show improvements in sprint performance during team games exercise with carbohydrate ingestion, perhaps due to the lack of influence of carbohydrate on sprint performance when endogenous muscle glycogen concentration remains above a critical threshold of ∼200  mmol/kg dry weight. Despite the increasing number of publications in this area, few studies have attempted to drive the research base forward by investigating potential modulators of carbohydrate efficacy during team games exercise, preventing the formulation of optimal carbohydrate intake guidelines. Potential modulators may be different from those during prolonged steady-state exercise due to the constantly changing exercise intensity and frequency, duration and intensity of rest intervals, potential for team games exercise to slow the rate of gastric emptying and the restricted access to carbohydrate-electrolyte solutions during many team games. This review highlights fluid volume, carbohydrate concentration, carbohydrate composition and solution osmolality; the glycaemic index of pre-exercise meals; fluid and carbohydrate ingestion patterns; fluid temperature; carbohydrate mouthwashes; carbohydrate supplementation in different ambient temperatures; and investigation of all of these areas in different subject populations as important avenues for future research to enable a more comprehensive understanding of carbohydrate ingestion during team games exercise.

Carbohydrates for training and competition

An athlete's carbohydrate intake can be judged by whether total daily intake and the timing of consumption in relation to exercise maintain adequate carbohydrate substrate for the muscle and central nervous system ("high carbohydrate availability") or whether carbohydrate fuel sources are limiting for the daily exercise programme ("low carbohydrate availability"). Carbohydrate availability is increased by consuming carbohydrate in the hours or days prior to the session, intake during exercise, and refuelling during recovery between sessions. This is important for the competition setting or for high-intensity training where optimal performance is desired. Carbohydrate intake during exercise should be scaled according to the characteristics of the event. During sustained high-intensity sports lasting ~1 h, small amounts of carbohydrate, including even mouth-rinsing, enhance performance via central nervous system effects. While 30-60 g · h(-1) is an appropriate target for sports of longer duration, events >2.5 h may benefit from higher intakes of up to 90 g · h(-1). Products containing special blends of different carbohydrates may maximize absorption of carbohydrate at such high rates. In real life, athletes undertake training sessions with varying carbohydrate availability. Whether implementing additional "train-low" strategies to increase the training adaptation leads to enhanced performance in well-trained individuals is unclear.