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This is actually on intramuscular fat but it also provides some nice insights on elite physiology.
Well, taking into account all this, especially the important bioenergetic argument, the question is: How to train and eat to improve the composition and localization of GIMTs? To answer this question, we can only look at professional endurance athletes. What are they doing?
Training a lot, but well. If we look at the history of any World Tour cyclist, we can see months in which they train from 80 to 110 hours. Similarly, if we analyze the records of the best runners or triathletes in the world, we find weeks of> 180 km or> 35h, respectively. A long, long time, a lot of volume. But at what intensities? Important. Is it possible to train 90 hours a month at a high intensity? Or even at a medium intensity? No. If we go back to these records we see that the distribution of the intensities is very significant: The time line elapsed at low intensities (Z1-Z2) is> 5 times higher than that of a medium intensity (Z3) and> 10 times more than that of high intensities (Z4-Z5). And we professionals who dedicate ourselves to working with them know this well.This large volume makes it easier for them to mobilize metabolic resources related to the use of fatty acids and, more specifically, to TGIM, generating adaptations that allow them to oxidize them in the mitochondria with high efficacy and efficiency.
What about nutrition? Do we look again at the best athletes in the world? This time, I can also bring in more information from my own work, so let’s take a deeper look. Training at a low intensity does not mean that the metabolic demand is low. Do you know at what relative intensity a professional WT cyclist has his ventilatory threshold 1? At the same, or even above, that an amateur athlete can obtain his ventilatory threshold 2. But, also, do you know that a quality of these athletes is their high capacity to produce energy? They are Formula 1 engines, so their production is very high, but without losing efficiency, on the contrary, improving it. A professional cyclist can generate more energy (kcal / min) than an amateur athlete at the same intensity, and that is a very good thing (contrary to what it may seem) because it translates into more mechanical energy (with more% than the amateur, by the way), in more watts. These cyclists are better at everything, at producing, at spending, at doing it efficiently, and at creating and resynthesizing what they spend. All this means that, despite training at low-moderate intensities for them, the metabolic stress they endure is very high. For example, an athlete can consume 18-20kcal / min at a moderate intensity. If you multiply by a 3h workout, you can get a calculation of> 3000 kcal. Do you understand the high demand for these athletes? How do they supply it?
One of the main factors that most determine the ability to train is taking in a lot of energy. Of course these athletes do. But, in addition, eating an energy that allows you to train a lot of volume at high metabolic stress. And these cyclists do this too. They consume high amounts of carbohydrates, not only during exercise, but also outside of it (although to a much lesser extent). But at low and moderate intensities? Let me ask you one more thing. How many g / min of glucose do you think a “motor” of these consumes at an intensity of VT1? The answer is a lot, exactly> 1.8-2g / min. Do hourly calculations, if you want. Therefore, the oxidation of glycogen and glucose is high at these intensities, as much as we want to understand this zone as a “magic zone” in which only fatty acids are used. Therefore, its replacement is decisive. As for the “magic zone”, by the way, we should not think that carbohydrate intake limits fat oxidation, or rather, the ability to generate related adaptations, because that is not the case. L he athletes with the highest rates of fat oxidation that I have been able to measure are those who ingest carbohydrates the most, especially during exercise. In addition, the role of glycogen in muscle contraction, recovery, subsequent signaling and metabolic adaptation related to mitochondrial biogenesis is so important that directly compromising it leads to states of overtraining and the inability to train which necessary to generate the adaptations of which we speak.
Summarizing. Improving the TGIM will depend, to a large extent, on the volume and distribution of the intensity of the exercise. High volumes are associated with better adaptations. To train these volumes, especially as the athlete’s level increases, it is necessary to provide energy and, more specifically, sufficient carbohydrates, always ensuring a considerable availability of lactate and liver and muscle glycogen.