PUSHING THE LIMITS OF HUMAN PERFORMANCE: ARE 120 G/H OF CARBOHYDRATES THE KEY?

During exercise, energy comes from several substrates, especially fat and carbohydrates, with carbohydrates stored in the body as glycogen. Their contribution varies with exercise intensity, and carbohydrates become the main source during moderate- and especially high-intensity work. Depletion of glycogen stores therefore limits performance during high-intensity exercise. This explains why athletes consume carbohydrate-rich sports drinks, gels and bars during competition: they provide energy for intense efforts and preserve glycogen stores. But how much carbohydrate should they consume?

Traditional carbohydrate-intake recommendations

Until recently, standard guidelines recommended approximately 60 grams of carbohydrate per hour of exercise. The assumption was that the transporters used to move carbohydrates into cells had this maximum capacity, with an even lower limit for slowly oxidized carbohydrates such as fructose or galactose. Later studies showed that the amount could increase when combining carbohydrates that use different transporters to enter the cell, such as glucose and fructose. Studies led by sports dietitian Asker Jeukendrup found that very high doses—between 108 and 144 g/h—of a glucose-fructose mixture increased carbohydrate oxidation and improved performance not only compared with placebo, but also compared with the same carbohydrate dose from glucose alone.1,2

New findings on carbohydrate intake

Based on these findings, the past decade has seen recommendations of up to 90 g/h of carbohydrate, especially for events lasting more than 2 hours,3 because intestinal absorption was thought to prevent further oxidation benefits at higher doses. Most cyclists consume this amount, as discussed in a recent post. Recent evidence has challenged that limit. Studies led by Spanish sports dietitians Aritz Urdampilleta and Aitor Viribay found that trail runners consuming 120 g/h reported lower perceived load and neuromuscular fatigue and showed less muscle damage—including lower creatine kinase—after a trail race than runners consuming 60 g/h or 90 g/h, the doses more commonly used.4,5 Despite important limitations, including only 6 to 7 runners per group and a parallel rather than crossover design, these studies offer a new perspective. In athletes accustomed to high carbohydrate intake—the participants consumed 90 g/h in at least two weekly sessions during the 4 weeks before the race—tolerance may be much greater than previously thought. Another recent study gave 120 g/h as a drink, gels or jelly to 9 cyclists during a 3-hour moderate-intensity trial. Participants oxidized much of the carbohydrate without gastrointestinal symptoms.6 An intake of 120 g/h therefore appears feasible, at least after appropriate gut training, and could extend performance limits. This is consistent with observations from professional cyclists in the Vuelta a España 5 years ago: average intake was 90 g/h during stages and approached 120 g/h in some.7

Conclusions
Science continues to push the known limits of human performance. High carbohydrate intakes—60 g/h for efforts lasting up to 2 hours and more for longer events—are generally beneficial. However, the association between carbohydrate intake and performance may not be linear: increasing intake from 30 to 60 g/h may provide greater benefits than increasing from 90 to 120 g/h.8 More large-scale studies are also needed to confirm whether very high intakes, reaching the widely discussed 120 g/h, meaningfully improve performance and prevent glycogen depletion.9 Current evidence nevertheless suggests that appropriate gut training can enable athletes to tolerate and oxidize very high carbohydrate doses, potentially providing additional performance benefits.

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References
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2. Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008;40(2):275-281. doi:10.1249/mss.0b013e31815adf19
3. Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29(SUPPL. 1):37-41. doi:10.1080/02640414.2011.585473
4. Urdampilleta A, Arribalzaga S, Viribay A, Castañeda-Babarro A, Seco-Calvo J, Mielgo-Ayuso J. Effects of 120 vs. 60 and 90 g/h carbohydrate intake during a trail marathon on neuromuscular function and high intensity run capacity recovery. Nutrients. 2020;12(7):1-17. doi:10.3390/nu12072094
5. Viribay A, Arribalzaga S, Mielgo-ayuso J, Castañeda-babarro A. Effects of 120 g/h of Carbohydrates Intake during a Mountain Marathon on Exercise-Induced Muscle. Nutrients. 2020;12.
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7. Muros JJ, Sánchez-Muñoz C, Hoyos J, Zabala M. Nutritional intake and body composition changes in a UCI World Tour cycling team during the Tour of Spain. Eur J Sport Sci. 2019;19(1):86-94. doi:10.1080/17461391.2018.1497088
8. Smith JW, Pascoe DD, Passe DH, et al. Curvilinear dose-response relationship of carbohydrate (0-120 g??h-1) and performance. Med Sci Sports Exerc. 2013;45(2):336-341. doi:10.1249/MSS.0b013e31827205d1
9. Podlogar T, Bokal Š, Cirnski S, Wallis GA. Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h−1 versus 90 g h−1 at different ratios. Eur J Appl Physiol. 2022;122(11):2393-2401. doi:10.1007/s00421-022-05019-w