In a previous blog we discussed what it takes to run a sub 2h marathon. Nutrition is an important factor, and in particular race nutrition has received a lot of attention recently. Here we will discuss how smaller athletes can benefit more from high carbohydrate intakes than larger athletes. It is a point Trent Stellingwerff and I made almost 10 years ago (1) in response to a paper on running sub 2h (2).
Carbohydrate during endurance events improve performance
Carbohydrate intake during prolonged events (>90min) can improve exercise performance, compared with no intake or water alone. The rate limiting step for carbohydrate delivery to the muscle appears to be the absorption in the intestine (3). Transport proteins in the intestine that are responsible for transporting carbohydrates across the intestinal wall become saturated (see this blog where this is explained in more detail). There are studies suggesting that a greater carbohydrate intake can be beneficial. We discussed this is several earlier blogs (see list at the bottom of this blog).
Endurance athletes and gastro-intestinal problems
However, 15-20% of endurance athletes have a chronic history of GI problems during prolonged exercise (4) and not ingesting larger amounts of carbohydrate may prove challenging or even unpractical. It is also known that exogenous carbohydrate oxidation is independent of body weight. In other words lighter and heavier athletes will use the same amount of carbohydrate from a drink (3).
What does all this mean for a marathon runner? Smaller runners may have a relative advantage. If oxidation rates max out at 1 g/min, then a 56kg runner is able to oxidize 20% more per kg BW compared to the 70kg runner (1.07 vs. 0.86g CHO/kg body weight/h) (1). For similar reasons it has been argued that smaller runners have thermoregulatory advantages compared with heavier runners. In a commentary a few years ago we argued that smaller runners may have a distinct advantage in term of exogenous carbohydrate oxidation and its contribution to total energy expenditure compared with heavier runners.
Smaller runners may have a distinct advantage in term of exogenous carbohydrate oxidation and its contribution to total energy expenditure compared with heavier runners.
Carbohydrate intake and running sub 2
Therefore, alongside having a very high VO2max, lactate-threshold and running economy values, we further proposed that it will be prerequisite for this athlete to have an individualized and aggressive fueling plan coupled with a good tolerance for high carbohydrate intake (1). We suggested that whoever would break the 2 hour barrier would have to be light and take in carbohydrate at a high rate during their event. Where runners used to take very small amounts of carbohydrate (if at all), Haile Gebrselssie may have been one of the first runners to use high carbohydrate intakes. It is said that Kipchoge’s intake during the sub 2h marathon challenge was 100g/h with a mixture of maltodextrin and fructose.
Stellingwerff T, Jeukendrup AE. Commentaries on Viewpoint: The two-hour marathon: Who and when? J Appl Physiol 110: 278–293, 2011; Letter To The Editor doi:10.1152/japplphysiol.01259.2010
Joyner MJ, Ruiz JR, and Lucia A. The Two-Hour Marathon: Who and When? J Appl Physiol.
Jeukendrup AE. Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care 13: 452-457, 2010.
Pfeiffer B, Cotterill A, Grathwohl D, Stellingwerff T, and Jeukendrup A. The effect of carbohydrate gels on gastrointestinal tolerance during a 16km run. Int J Sport Nutr Exerc Metab 19: 485-503, 2009.