During our conversations with athletes, we receive many questions about the “best” number of servings to use. For longer and/or more demanding sessions, taking 2 or more doses can be more than appropriate. But why? This article aims to answer that question.
Role of Carbohydrates
Carbohydrates are the body’s main energy source. They can be used immediately or stored as glycogen in the liver and muscles.
During exercise, muscle glycogen is converted back into glucose, which is used by muscle fibers as a source of energy. The liver, meanwhile, converts glycogen into glucose to be released into the bloodstream to maintain blood glucose levels.
Thus, during exercise, glycogen stores are depleted, and eventually—when liver glycogen stores are exhausted (typically after 90 to 120 minutes of continuous vigorous effort)—blood glucose levels drop. This hypoglycemia, or what is commonly called in sports circles the “bonk” or “hitting the wall,” compromises power, coordination, and judgment.
Carbohydrate intake during exercise can therefore help delay glycogen depletion and thus prevent hypoglycemia.
Personally, races during which I underestimate the required intake are, unfortunately, still too frequent! And yet, calculating what’s needed is simple—and makes all the difference. With training, my “wall” has gone from repeated pauses, to walking, then to a sluggish jog. The wall—or the infamous “bonk”—now comes later, both in time and distance. I’m always amazed by the impact of finding the right amount of carbohydrates: my pace stays steady, I have the energy to shave off precious minutes, or to finish a quality training session.
Amount of Carbohydrates to Consume During Exercise
Carbohydrates are the most efficient energy source to use during exertion.
The amount of carbohydrates to consume during exercise varies depending on the duration and intensity, the objective of the training session, and body composition.
In general, it has been established that for exercises under 30 minutes, water is sufficient. For exercises lasting 45 to 75 minutes with high intensity, a small amount of carbohydrates or a mouth rinse is recommended. For exercises lasting 1 to 2 hours, 30–60g/h should be ingested—and likely closer to 60g as duration and intensity increase.
Finally, for intense efforts lasting more than 2.5 hours, intakes of 90 g or more per hour of carbohydrate combinations using different intestinal transporters (such as our Maltodextrin-Fructose blend in a 2:1 or 1:0.8 ratio) are recommended, if the athlete can tolerate it digestively (this tolerance can be developed). This combination is important because the body’s capacity to use (oxidize) glucose or maltodextrin is limited to 60 g/h (saturation of the SGLT1 transporters). The addition of 30 g/h of fructose provides an additional oxidative pathway, as fructose is absorbed through a completely different mechanism and is not affected by SGLT1 saturation. Our Maltodextrin-Fructose formula is therefore optimal for meeting needs of 90 g/h.
For me, the transition to a drink composed of multiple carbohydrate sources instead of one predominant type was fairly subtle, but I noticed it more during high intake (more than 60 g per hour) and after several hours. If I push too much on one type of carbohydrate at a time, I feel like my stomach is too full—like after a big meal. It doesn’t stop me from functioning, far from it—but a drink that includes both Maltodextrin & Fructose doesn’t give me that sensation, even in large quantities.
Central Fatigue and Cognitive Performance
During prolonged efforts, it’s not only the muscular system that gets tired. The brain plays a key role in performance, notably through the regulation of motivation, motor coordination, and perception of effort. This so-called "central" fatigue is influenced by the availability of glucose—the primary fuel of the nervous system.
An adequate carbohydrate intake helps maintain a stable level of blood glucose, thus reducing the sensation of mental fatigue and supporting executive functions. This results in a better ability to make decisions, maintain pace, and stick to a race strategy—even when physical fatigue sets in.
The mouth contains sensory receptors that detect carbohydrates (such as sugar). These receptors send signals to the brain, particularly to areas associated with pleasure, reward, and motivation: this is the dopaminergic system. Carbohydrates also stimulate oral and neural receptors associated with the dopaminergic system, which can improve mood and motivation—even without full ingestion. Studies have shown that simply rinsing the mouth with a carbohydrate solution activates brain areas related to reward and performance (Chambers et al., 2009).
Benefits of carbohydrate intake on the brain:
Reduction in mental fatigue.Sustained rhythm and strategy.
Improved motor coordination.