Guidelines 10 years ago indicated that carbohydrate intake during exercise should be 30-60 grams per hour. In some situations, this led to an intake of 90 g/h. However, an article was recently published that suggested an intake of 120 g/h in mountain marathon runners. Time to investigate.

It has long been believed that carbohydrate oxidation from ingested beverages, gels and bars can be utilized (oxidized) by the body at rates of up to 60 g/hr. For example, if an endurance athlete eats 100 g/h, he burns up to 60 g/h. The rest is likely to remain in the gut and this is associated with gastrointestinal problems. Now we know that the limitation is intestinal absorption and that this limitation can be overcome by using different types of carbohydrates that use different intestinal transporters for absorption. In short, certain carbohydrate combinations can be oxidized much faster. In a study it was found that combinations of glucose and fructose can be oxidized up to 105 g/h. This happened at very high intake levels of 144g/h.

However, such high intakes are not recommended for every athlete. Most must first train their gut to be able to absorb such high amounts. That's why the recommendations so far have been around 90 g/h, as a compromise between sufficient carbohydrate intake, but not so much that many athletes would experience gastrointestinal problems. It is important to note that intakes higher than 90 g/h could theoretically have positive effects as we had observed higher oxidation rates at higher intakes.

The researchers hypothesized that higher carbohydrate intake could not only increase performance but also reduce post-workout muscle damage. They therefore designed a study to compare the effects of a high carbohydrate intake of 120 g/h versus 90 g/h and 60 g/h intakes in 26 elite male ultra-endurance athletes during a mountain marathon. They were randomly assigned to one of the experimental groups and trained to use this target capture during training. So the high carbohydrate intake was nothing new to the group.

Researchers measured exercise load by asking for ratings of perceived exertion and several markers of muscle damage (creatine kinase (CK), lactate dehydrogenase (LDH), glutamic-oxaloacetic transaminase (GOT), urea, and creatinine). EIMD markers were analyzed before the race and 24 hours after, and it was found that the 120 g/h group had significantly lower CK, LDH and GOT levels than 60 or 90 g/h 24 hours after the mountain marathon.

Internal stress and muscle damage were significantly lower 24 hours after the race in the group consuming 120 g/h of carbohydrates. Based on the assessments of the perceived exertion during the event, the researchers were able to calculate an internal load and concluded that the internal load during the mountain marathon was 120 g/h, which was significantly lower than that of 60 and 90 g/h.

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