Carbohydrates to Improve “Durability” in Endurance Sports

Carbohydrates and endurance in sports: key to performance

What is durability in endurance sports?

Performance in endurance sports is determined by a multitude of components, ranging from physical to technical or tactical. Among the former, three key indicators have traditionally been proposed to explain athletes' performance: maximum oxygen consumption (VO2max), the so-called 'anaerobic threshold,' and exercise economy. The combination of these three elements has been considered for years the recipe on which sporting success was based.

However, in recent years a new factor has emerged that could be decisive for performance: durability. Imagine an athlete who in a stress test shows a very high VO2max or who in a field test displays a very high anaerobic threshold. While these indicators measured in “fresh” conditions may be relevant, they will be of little use if they are not able to maintain those figures after hours of effort, when they need to make a breakaway or a sprint.

Increasingly, performance in endurance sports, especially in some such as cycling, relies on the ability to apply very high power values in critical race situations after hours or even days of effort (as in a stage race). That ability to mitigate the drop in performance under conditions of fatigue is what is considered durability.

Relationship between carbohydrates and sports performance

Mechanism of carbohydrates in fatigue

As we have seen in previous articles, carbohydrates are taking on a leading role in athletes' nutrition. Although when we exercise at low intensity fats are the main energy substrate, as intensity increases, carbohydrates become more relevant. That is why, in competition, the depletion of glycogen stores represents a limiting factor for performance.

This physiological basis explains why athletes consume foods rich in carbohydrates (sports drinks, gels, bars, etc.) during competitions. In fact, we know that cyclists, considered the standard-bearers of endurance sports, consume large amounts of carbohydrates (90 and up to 120 grams per hour). But what role do these play in fatigue resistance or endurance?

Scientific evidence: recent studies

Until recently, many studies showed that carbohydrate consumption during a test (for example, a 2-hour time trial) improved performance, but the effects on durability, understood as the drop in performance after accumulated fatigue, were unknown.

However, in recent years the evidence suggests that carbohydrates could improve this indicator. A study evaluated performance in a maximum test of 3 minutes without prior fatigue and after 2 hours of moderate-intensity effort, comparing the effects of consuming 60 grams of carbohydrates per hour with a placebo. The results showed that athletes who consumed carbohydrates maintained their performance after 2 hours of effort, while those who took a placebo experienced a 7% drop (254 W versus 236 W).

Another recent study analyzed the effects of carbohydrates on endurance in cyclists and triathletes. They performed an exercise test before and after 2 hours and a half of cycling at moderate intensity. The participants repeated the same protocol consuming carbohydrates (60 grams per hour) or a placebo. As expected, the power associated with the thresholds in the exercise test decreased with fatigue, although to a lesser extent when consuming carbohydrates. Specifically, the first threshold dropped by 6% with placebo and only by 3% with carbohydrates.

Moreover, carbohydrate consumption managed to maintain stable blood glucose levels, whereas in the control group these decreased at the end of the test. This is one of the main mechanisms that support carbohydrate consumption during prolonged exercise. Despite the progressive depletion of muscle glycogen, carbohydrate consumption can attenuate the depletion of liver glycogen, preventing hypoglycemia.

How to optimize carbohydrate intake to improve durability

We see how carbohydrate consumption during exercise (in this case, 60 grams per hour, although the amount may vary depending on the duration and intensity of the test) can attenuate the deterioration of physiological markers such as thresholds or performance after accumulated fatigue.

These results are of vital importance in long-duration tests such as cycling, where success depends on the ability to perform efforts at high intensity under conditions of fatigue.

Conclusions

• The consumption of carbohydrates during exercise helps maintain performance under conditions of fatigue.
• Improves resistance to the drop of the anaerobic threshold after several hours of effort.
• Avoid hypoglycemia by keeping blood glucose levels stable.
• It can be key in endurance competitions where performance in critical situations makes the difference.

Therefore, endurance not only depends on an athlete's initial physiological capacity, but also on their nutritional strategy, especially regarding carbohydrate intake.

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Author

Pedro Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR of Madrid).
Web: www.fissac.com

References

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2           Maunder E, Seiler S, Mildenhall MJ, et al. The Importance of ‘Durability’ in the Physiological Profiling of Endurance Athletes. Sport Med 2021; 51(8):1619–1628. Doi: 10.1007/s40279-021-01459-0.

3           Clark IE, Vanhatalo A, Thompson C, et al. Dynamics of the power-duration relationship during prolonged endurance exercise and influence of carbohydrate ingestion. J Appl Physiol 2019; 127(3):726–736. Doi: 10.1152/japplphysiol.00207.2019.

4           Dudley-Rode H, Zinn C, Plews DJ, et al. Carbohydrate ingestion during prolonged exercise blunts the reduction in power output at the moderate-to-heavy intensity transition. Eur J Appl Physiol 2024; (0123456789). Doi: 10.1007/s00421-024-05687-w.

5           Gonzalez JT, Fuchs CJ, Smith FE, et al. Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists. Am J Physiol – Endocrinol Metab 2015; 309(12):E1032–E1039. Doi: 10.1152/ajpendo.00376.2015.