Among all fatigue factors, nutritional strategies target “one” of them in particular: muscle biochemistry. This is affected as much by the nature of the energy sources you use as the efficient use of this energy by your muscles. To see more clearly, we propose a 4-part dossier on nutritional strategies related to carbohydrates that are used in endurance sports. Here is the introduction.
Today, for each use of a nutritional strategy, we systematically distinguish 2 temporalities:
– The time of the competition. Or what are the energy requirements for maximum performance?
– That of training. Or how to boost “adaptations” useful for competition?
The concern, however, is that between these two contexts the organism does not make the difference “a priori”: it does not know if its goal is performance or if it is adaptation, whereas each one presupposes very different subbases. So here you see the function of nutritional manipulation, which will be to whisper to the body a subtle message: accentuate VS. limit the state of fatigue.
THE CARBOHYDRATE-EXERCISE RELATIONSHIP.
Several energy sources are involved simultaneously with the exercise. You know that. But primarily there is a preponderance between these sources, which is dictated by the intensity of the exercise, first, and your level of training and diet, then. In numbers, we have:
– Above 60% VO2max, carbohydrates are the main source of energy.
– At ~85% VO2max, the use of carbohydrates is 10x more important than that of fats. They represent ~85% of the total energy supplied.
In Ironman distance triathlon, it is known that the average athlete is at 80-85% VO2max. When we look at the carbohydrate contribution at this level of intensity, we better understand the interest in “energy efficiency”: the athlete must learn to run faster by consuming as much/less carbohydrates.
CARBOHYDRATES IN COMPETITION.
For half- and full-ironman, an athlete’s energy demand is ~4500 kcal and ~10000 kcal, respectively. Of these ~10000 kcal, ~6000 kcal are from the degradation of the body’s initial stocks of carbohydrates and fats (including ~2000 kcal from the 500g of muscle and liver reserves). The other ~4000 kcal come from contributions made during the race: for more than 90% of athletes, these contributions are based on carbohydrates.
If we look at the qualitative aspect, then we notice that the intake of carbohydrates in competition must be dependent on their type. In fact, it is the type of carbohydrate that influences the body’s ability to oxidize it, and therefore use it as muscle fuel. But the use of carbohydrates is also capped: the body does not manage to consume an unlimited quantity of carbohydrates… In this framework, we advise you a ration combining glucose and fructose because this ration supposes the use of 2 intestinal carriers of carbohydrates, which has several consequences :
– Using these 2 types of carriers increases the carbohydrate degradation rate from ~1g.min to ~1.5g.min (i.e. ~90g.h) (and sometimes up to ~1.8g.min). In practical terms, such a rate can be achieved with water, gels and bars. What does vary, however, is the composition of these products (with or without fibre, fat, protein, caffeine…) which requires you to familiarize yourself with the training at least 2-3 weeks before the competition.
– They limit the risk of gastric disorders which are linked to the saturation of a carrier.
On this basis, the carbohydrate intake during an event is recommended very globally between ~30 and ~90g.h, with a dosage depending on the duration of the race and individual needs. But when it comes to performance, “the more the better” within this window! If some athletes support grammages > 90g.h, ~80g.h are advanced by several studies as an optimum while ~20g.h of carbohydrates seem a minimum to begin to detect benefits.
The interest of a carbohydrate intake is demonstrated in all events exceeding 60-90min. This is explained in particular by the time needed for their assimilation by the body. But be aware that carbohydrates also have an almost immediate non-metabolic effect. In other words, they are also useful for performances <60′. In what context? As part of their passage into the mouth simply !
Yes, the receptors present there stimulate the motor areas of the brain through the reward circuit. Therefore, one can think that in competition the rinsing of mouth (~10” consecutive, without ingestion) containing sweetened drinks is a useful strategy, especially when it is hot and avoiding overhydration is important.