The role of carbohydrates in endurance training and performance
Part 2: Practical Recommendations for Carbohydrate Strategies
An article written by Sophie Herzog, Øyvind Sandbakk, Trond Nystad and Rune Talsnes, with expert inputs by Dr. Tim Podlogar
Introduction
Over the years, we have observed firsthand the difference adequate carbohydrate fueling can make. Athletes recovering from underperformance or struggling with heavy training loads have often experienced significant breakthroughs simply by optimizing their carbohydrate intake during and around training. In fact, anecdotally, athletes with higher carbohydrate availability often report greater resilience to high training loads, improved recovery and better training quality – supporting long-term adaptations
Building on the scientific foundation from Part 1, this article focuses on practical strategies for incorporating carbohydrates into endurance training. The aim is to bridge the gap between knowledge and application, empowering athletes to fuel effectively for improved performance, recovery, and long-term health.
Pre-competition/Very demanding training sessions
Starting an event with adequate muscle glycogen stores is important to optimize endurance performance. Consequently, several strategies have been proposed to maximize muscle glycogen synthesis in the days leading up to competition - also known as carbohydrate or glycogen loading (Hawley et al., 1997).
Carbohydrate loading: 36–48 h before competitions lasting > 90 minutes: Consume 10–12 g of carbohydrates per kilogram of body mass to maximize muscle glycogen stores (Thomas et al., 2016)
Pre-event meal: After an overnight fast, liver glycogen stores are typically reduced by ~25% (Iwayama et al., 2021). A pre-event meal containing 1–4 g fructose-glucose-based carbohydrates per kilogram of body mass helps stabilize blood glucose levels during the competition and optimizes performance (Burke et al., 2011). The size of the meal, i.e., the amount of carbohydrates recommended to ingest, depend on the time to digest before competition. As a rule of thumb, 1 g/kg for every hour before is recommended (see Figure 1). In practical terms, this means that if you have your breakfast 2 hours before the start, 2 g/kg would be recommended, with the majority of the carbohydrates coming from glucose (e.g., white rice) and adding some fructose through jam, honey, syrups or fruit juices.
This combination of glucose-fructose-based carbohydrates was found to provide superior exercise capacity compared to glucose-only carbohydrates (Podlogar et al, 2022) and it is expected that general guidelines will be updated with more nuanced recommendations based on the timing and the type of carbohydrates to be ingested.
Figure 1: Breakfast before competition (Image credits mysportscience) https://www.mysportscience.com/post/race-day-breakfast-considerations
During competition
The optimal carbohydrate intake during competition depends on the duration, intensity, goal of the competition or training, absolute performance[1] and individual tolerance.
General Guidelines:
<30 minutes: No carbohydrate intake is necessary, as there’s minimal evidence of performance benefits for short durations.
45-75 minutes: A carbohydrate mouth rinse or intake of ~30 g/hour can improve performance at very high intensity. Choose based on practicality and conditions (e.g., temperature, accessibility). At this duration, the type of carbohydrate doesn’t seem to make a significant difference.
Prolonged exercise: For sessions lasting 1-2 hours, carbohydrate intake has been shown to boost performance, with around 30 grams per hour being sufficient. As exercise duration or intensity increases, so should carbohydrate intake - up to 60 grams per hour, and for efforts exceeding 2.5 hours, 90-120 grams per hour depending on tolerance. Very high carbohydrate intakes of 120g/h and higher are increasingly common among elite endurance athletes, but there is only very little evidence to proof that this high intake is performance-enhancing or superior for recovery (e.g., during a multi-day event like the Tour de France) (Viribay et al., 2020). While it is now common practice for elite athletes who intend to take in high carbohydrate intakes during their races to also “train their gut” to tolerate higher amounts, itI seems that the major limitation is absorption, which is highly individual and there is currently no evidence that it can be improved with gut training (Burke et al, 2021).
Figure 2: Carbohydrate intake during exercise (Image credits mysportscience): https://www.mysportscience.com/post/2015/05/27/recommendations-for-carb-intake-during-exercise
Insights for Application
Experimenting with different carbohydrate sources (e.g., gels, drinks, bars, “real” food) and adjusting strategies based on environmental conditions can help to determine your best individual practice. Furthermore, for some athletes, simply increasing carbohydrate intake in training can lead to noticeable improvements in training adaptation, recovery and performance. However, other athletes must overcome psychological barriers, such as fears of weight/fat gain - which can be a hindrance to optimal nutrition. Addressing this fear requires education and a shift in mindset, emphasizing the importance of adequate energy (and carbohydrate) availability for sustaining high training loads, achieving peak performance and career longevity.
In cases where deeper challenges, such as disordered eating or eating disorders, are at play, the path to improvement is more complex and often requires a longer, more holistic approach.
More practical information that can help you adjust your in-race fuelling[1]:
Post-competition/training recovery practices
Success in endurance sport is shaped both by the training performed and how the organism can adapt to those stimuli. In this context, nutrition has an important role in optimizing recovery, adaptation and subsequent performance. Since endogenous glycogen stores are a key determinant of endurance performance and capacity, rapid post-exercise glycogen repletion becomes a priority when athletes need to restore performance within a limited time frame, such as in multi-day events or back-to-back training sessions. Therefore, both the timing and composition of nutrition matter and post-exercise recovery involves a complex interplay between muscle and liver glycogen restoration.
Research has shown that post-exercise liver glycogen repletion can be significantly accelerated by consuming glucose in combination with fructose or sucrose, nearly doubling the replenishment rate compared to glucose alone (see Figure 3, Gonzalez et al., 2016, Podlogar et al., 2022). This suggests that optimizing carbohydrate intake post-exercise can enhance liver glycogen recovery, which is crucial for sustaining blood glucose levels during subsequent training sessions.
Full muscle glycogen replenishment, on the other hand, can take up to 24 hours or longer, particularly if there is muscle damage or carbohydrate intake was insufficient during exercise. However, a delay in carbohydrate intake post-exercise has also been shown to impair high-intensity exercise capacity the following day (Díaz-Lara et al., 2024). Additionally, neglecting proper fueling around training can lead to within-day energy deficits, which may cause metabolic perturbations, post-exercise cravings or excessive compensatory overeating - what we often refer to as “raiding the refrigerator.” This pattern can disrupt an athlete’s overall energy balance and hinder recovery.
Post-competition recommendations to maximize glycogen synthesis:
Timing matters: During the first 3-4 hours post-exercise, prioritize 1.2 g of carbohydrates per kilogram of body weight per hour to optimize glycogen replenishment (Thomas et al., 2016).
Optimal Combinations: Fructose-glucose mixtures have proven most effective for replenishing both muscle and liver glycogen stores after exercise (Maunder et al., 2018, Gray et al. 2019, Podlogar et al. 2023). Milk based carbohydrates (e.g., galactose and lactose) are good for replenishing liver but not ideal for the replenishment of muscle glycogen stores. However, chocolate milk, which contains both, milk derived carbohydrates and also table sugar (i.e., sucrose) is likely sufficient to optimize both liver and muscle glycogen stores.
Figure 3: Current evidence on optimal combinations of different carbohydrates. Image provided by Dr. Tim Podlogar
Conclusion
Carbohydrate strategies are not a one-size-fits-all approach and must be tailored to the athlete’s goals, exercise duration and intensity, and personal utilization and absorption rates. Furthermore, a comprehensive nutritional strategy should view pre-, during-, and post-exercise fueling as interconnected components, each essential for sustaining high performance.
By implementing these evidence-based recommendations, athletes can:
Maximize performance and recovery.
Maintain training consistency.
Build a strong nutritional foundation for long-term development.
[1] We would like to thank MySportScience for allowing us to use some of their graphics and for the valuable work they do in translating science into practice.
References
Podlogar T, Cirnski S, Bokal Š, Verdel N, Gonzalez J. Addition of fructose to a carbohydrate-rich breakfast improves cycling endurance capacity in trained cyclists. Int J Sport Nutr Exerc Metab. 2022
Podlogar T, Shad BJ, Seabright AP, Odell OJ, Lord SO, Civil R, Salgueiro RB, Shepherd EL, Lalor PF, Elhassan YS, Lai YC, Rowlands DS, Wallis GA. Postexercise muscle glycogen synthesis with glucose, galactose, and combined galactose-glucose ingestion. Am J Physiol Endocrinol Metab. 2023 Dec 1;325(6):E672-E681. doi: 10.1152/ajpendo.00127.2022. Epub 2023 Oct 18. PMID: 37850935; PMCID: PMC10864004.
Hawley JA, Schabort EJ, Noakes TD, Dennis SC. Carbohydrate- loading and exercise performance. An update. Sports Med. 1997;24:73–81. http:// www. ncbi. nlm. nih. gov/ pubmed/92915 49.
Iwayama K, Tanabe Y, Tanji F, Ohnishi T, Takahashi H. Diurnal variations in muscle and liver glycogen differ depending on the timing of exercise. J Physiol Sci. 2021;71:35. https:// doi. org/ 10.1186/ s12576- 021- 00821-1.
Thomas DT, Erdman KA, Burke LM. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48:543–68.
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29:S17-27. https:// doi. org/ 10. 1080/ 02640 414. 2011. 585473
Viribay A, Arribalzaga S, Mielgo-Ayuso J, Castañeda-Babarro A, Seco-Calvo J, Urdampilleta A. Effects of 120 g/h of carbohydrates intake during a mountain marathon on exercise-induced muscle damage in elite runners. Nutrients. 2020;12.
Burke LM, Hall R, Heikura IA, Ross ML, Tee N, Kent GL, Whitfield J, Forbes SF, Sharma AP, Jones AM, Peeling P, Blackwell JR, Mujika I, Mackay K, Kozior M, Vallance B, McKay AKA. Neither Beetroot Juice Supplementation nor Increased Carbohydrate Oxidation Enhance Economy of Prolonged Exercise in Elite Race Walkers. Nutrients. 2021 Aug 12;13(8):2767. doi: 10.3390/nu13082767. PMID: 34444928; PMCID: PMC8398364.
Gonzalez JT, Fuchs CJ, Betts JA, van Loon LJ. Liver glycogen metabolism during and after prolonged endurance-type exercise. Am J Physiol Endocrinol Metab. 2016 Sep 1;311(3):E543-53. doi: 10.1152/ajpendo.00232.2016. Epub 2016 Jul 19. PMID: 27436612.
Díaz-Lara J, Reisman E, Botella J, et al. Delaying post-exercise carbohydrate intake impairs next-day exercise capacity but not muscle glycogen or molecular responses. Acta Physiol. 2024; 240:e14215. doi:10.1111/apha.14215
Maunder E, Podlogar T, Wallis GA. Postexercise fructose– maltodextrin ingestion enhances subsequent endurance capacity. Med Sci Sports Exerc. 2018;50:1039–45. https:// journals.lww.com/ 00005 768- 20180 5000- 00018.
Gray EA, Green TA, Betts JA, Gonzalez JT. Postexercise glucose– fructose coingestion augments cycling capacity during short-term and overnight recovery from exhaustive exercise, compared with isocaloric glucose. Int J Sport Nutr Exerc Metab. 2020;30:54–61. https:// www. ncbi. nlm. nih. gov/ pubmed/31715 584.
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[1] https://www.mysportscience.com/post/2015/05/27/recommendations-for-carb-intake-during-exercise
