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Fat Metabolism Training in Endurance Sports

A healthy fat metabolism delays performance decline. But how do you train your fat metabolism? Our author conducted a self-experiment.

A good fat metabolism delays the decline in performance

I stare at the orange bars on the printed sheet of paper that Lorenz Leuthold is holding under my nose. “Your fat metabolism is practically non-existent”, he says dryly. The bars illustrate how much energy my body gets from fats and how much from carbohydrates under athletic stress. Basically, the better endurance trained someone is, the longer and under higher loads he or she can get energy from fats. While I have so far assessed my fitness as “quite okay”, the bars now reveal: At least my fat metabolism is running poorly underground: My maximum fat oxidation rate, as it is called in technical jargon, is 0.14 grams of fat per minute. Top endurance athletes reach values of a good 1 gram per minute, which is about seven times more. Lorenz Leuthold, movement scientist at the “Training & Diagnostics” performance center in Zurich, nods as I tell him about my regular hunger pangs during ski tours, long runs and competitions. Obviously, he is not surprised, because my carbohydrates burn like tinder, while the fats seem to push themselves away from any metabolization.

Metabolic striptease

Same place, one hour before: I step on my racing bike as if it was a matter of life and death. A mask, which makes it difficult for me to breathe, continuously measures the composition of my breathing gases, i.e. oxygen and carbon dioxide. The ratio of these gases shows whether the body is running predominantly on fats or carbohydrates. At the same time Lorenz Leuthold measures my heart rate. Thus, after the test it can be determined at which pulse and which power (watt) I burn the most fat proportionally. The test is short but painful: after a good ten minutes and at 253 watts I give up completely. But that is how it should be: This form of sprioergometry tests tests your performance to your personal maximum.

Not slow enough

“About nine out of ten athletes we tested have a poor fat metabolism,” says Leuthold. And this is quite common among top athletes, emphasizes the sports physiologist, who conducts spiroergometry tests with over a thousand athletes every year. The reason: The athletes do too few slow units and train for basic endurance in training zones that are too intense. “With three to five training units per week, most athletes don’t want to go very slowly because they think that it doesn’t help”, says Leuthold. “As a result, they automatically complete a medium-hard training that is neither fish nor bird.” Sports scientist Lorenz Leuthold rather propagates a polarized training routine, i.e. on the one hand very relaxed sessions in combination with very hard and intense training.

Energy depot fats

But how does the metabolism influence athletic performance at all? The body gets its energy mainly from either carbohydrates or fats. The only difference is that the carbohydrate stores in the cells are limited and must be protected during endurance exertion. If the strain lasts long and intensive, it is no longer possible to supply sufficient carbohydrates, because otherwise stomach problems may arise. On the other hand, fats have an almost unlimited energy potential – even in well-trained top athletes. Because the energy supply does not work without carbohydrates during intense exertion, one “breaks” as soon as these are used up. Therefore it is important to preserve carbohydrate reserves. “The goal is to train the Fatmax zone as close as possible to the anaerobic threshold”, says Leuthold. In this way, a lot of energy can be provided by the fat metabolism at higher performance levels. And: The longer the competition time, the more important. “Fat metabolism starts to take on the right weight from about two hours,” explains Joëlle Flück, expert in sports nutrition and President of the Swiss Sports Nutrition Society, on the phone. A few years ago, a Danish study examined the correlation between maximum fat burning rate and performance at the Ironman in Copenhagen by a few dozen athletes. With the result: The higher the rate, the faster the athletes ran to the finish line.

Individual pulse and watt ranges

All this sounds quite plausible to me. That is why I listen carefully to Lorenz Leuthold when he defines my fat metabolism areas and writes them down on a piece of paper. These differ markedly from person to person and lie between 50 and 80 percent of the maximum pulse rate. Individual performance diagnostics – although at around 300 francs an expensive piece of fun – therefore makes perfect sense, as Joëlle Flück confirms. My maximum fat burning range when cycling is around 130 beats per minute or 68 percent of my maximum heart rate. If you use your thumb, you can deduct ten beats for the corresponding range when running. By the way, the Fatmax zone does not burn the most calories, as is often mistakenly stated. Although the absolute fat burning is highest in this area, the most calories are consumed at very high intensities. According to experts, the fat metabolism is most efficient during a very relaxed fasting workout. Because if you fast for at least six to eight hours beforehand, the reserves are used up right from the start. “Fasting training in the individually determined training range is a shortcut, so to speak”, explains Lorenz Leuthold. He therefore fills my training plan with three such mandatory units per week, which should last about 45 to 60 minutes before breakfast at a pace just below my maximum fat-burning zone, specifically around 125 heartbeats per minute in my case. In addition, there are one or two longer basic endurance units which I am allowed to complete with filled carbohydrate stores (see box) and where the pulse rate should be around 135 beats per minute. Whether on foot or on the bike is not very important for the metabolism, says Leuthold, as long as the specific pulse ranges are adhered to.

Between one and three hours

What Joëlle Flück emphasizes: “If someone is not training for an ultra-event, sobriety training sessions should not last longer than 60 to a maximum of 120 minutes”. If, on the other hand, you start with full reserves and do not consume any carbohydrates during the training, the training can last three hours. Otherwise you will tire the body in the first place and there is even the danger of overtraining. Because if there is a lack of carbohydrates, you burn fat, but you also attack the muscle structure and the regeneration time is extended. This is why it is important to maintain or even increase your protein intake immediately after such training.

At a snail’s pace with pulse 125

So now I regularly tie my running shoes at six in the morning, with nothing but a cup of coffee in my stomach. Crawling out of bed works sometimes better, sometimes less well. What remains during the first two months: As soon as I start running, my pulse rate rises to high altitudes. Looking at the clock and being very careful not to let the number go over 125, I can hardly catch up with morning walkers and their dogs – at least not after a real training session. Even the slow basics And they strain the patience of my training partners because of my snail pace.

Radical High Fat Method

Especially in the field of top-class sports, a camp has formed in recent years that tries to improve fat burning with radical methods. “However, this only makes sense for extreme endurance events,” says Joëlle Flück. “400-metre runners or even half-marathon athletes hardly benefit at all.” One of the better known advocates is the Swiss long-distance triathlete Jan van Berkel: he has been working on his fat metabolism for a good three years. His current trainer, Dan Plews, is a great supporter of the “Low-Carb-High-Fat” diet (LCHF). In a blog post, the New Zealander describes the path that van Berkel has been following with him since 2016. During this time van Berkel significantly improved his maximum fat oxidation rate – from 0.7 to 1.2 grams per minute. On the Ironman bike course alone, Plews calculates, his athlete is now saving carbohydrates equivalent to 17 to 20 gels. Although van Berkel’s Ironman marathon best time fell from about three hours to 2:45. But whether this is really due to his good fat metabolism and the fact that he fills his stores mainly with fats and proteins instead of carbohydrates before training and competitions is scientifically highly controversial. “So far, no controlled study shows that the LCHF diet has a performance-enhancing advantage over high-carb,” says Joëlle Flück. Lorenz Leuthold stresses that experiments like those conducted by Jan van Berkel are nonsensical for amateur athletes. After all, professional triathlete van Berkel has not only radically changed his diet, but also adapted his training accordingly. “The change requires incredibly close supervision, something that an amateur athlete can hardly afford.” It’s much more worthwhile to work on the fat metabolism with specific training.

Day of truth

In my experiment I have therefore limited myself mainly to training. Nevertheless, I still have a sense of achievement: In the third month I notice how the early morning lap is much easier for me, my running speed can almost be called a race. Also, my pulse doesn’t explode immediately when I want to ride my bike up a hill. Are the first signs that my body is now running better on fat? “How long it takes for the fat metabolism to improve is highly individual”, says Lorenz Leuthold, “but as a rule, significant improvements should become apparent after a good three months. That is why – 14 weeks have passed since the first test – my control test is now due. With the mask tied around my head, I start to unwind. I start with 70 watts and every two minutes the resistance increases. At 250 watts I gasp. “One more step is possible”, says Leuthold mercilessly and adds a few more watts. At 270 watts I’m done and try not to fall off the bike with a high red head. Meanwhile Leuthold frees me from the uncomfortable mask and praises that I actually kicked 17 watts more than last time. But much more than the absolute wattage I am interested in my maximum fat oxidation rate. Full of expectation I look at the orange bars on the printed test protocol a few minutes after the test. And they show: my maximum fat oxidation rate has nearly doubled while my heart rate remained constant. This obviously explains my better watt values: Because I was able to save carbohydrates during low load, they were still available during high load. I celebrate, because getting up early seems to have been worthwhile after all. And I firmly intend to start the day once or twice a week in the future with a relaxed workout.

Text from Stephanie Schnydrig – This blog entry is provided by the Swiss magazine FIT for LIFE. If you want to regularly read interesting articles about running and endurance sports, click here

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