What is the point of a sports session on an empty stomach?

By Guillaume Peephole – Photos: Mizuno / Brooks / PEDaLED / Orbea / Hoka

Running, cycling or swimming on an empty stomach means doing your session in the morning shortly after waking up and before breakfast. But in reality, you can consider yourself fasting 6 hours after the last meal. A session in the evening just before dinner and on condition of not having consumed calories after lunch has the same advantages.tages. And the same drawbacks.

Apart from the advantagestagwhich can be linked to the organization of a busy day, a sports session on an empty stomach would allow you to lose weight or get in shape (approach the ideal weight) more quickly. An explanation for this: After a night's sleep and a last meal several hours ago, glycogen reserves (fuel for exercise) in the muscles and liver are reduced. After a few dozen minutes of effort, the body is then forced to draw primarily on fatty acids to obtain energy. Hence an additional use of this type of fuel during this session compared to an outing carried out in the middle of the day. So theoretically a more favorable relationship between the time spent and the use of fats. But it is not that simple.

An acceleration of weight loss

A kilo of excess fat is 9000 calories. And to lose weight, you have to spend more calories than you consume. It's math.

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When running, you burn around 500 to 700 calories per hour, depending on your weight and pace. When cycling, it's around 500 and when swimming, it's around 600. It would therefore take between 15 and 20 hours of one of these so-called endurance sports without changing the usual caloric intake to lose an extra kilo.. This is a lot, especially since the preferred consumption of reserve fats implies adopting a relatively slow pace, therefore less rich in caloric expenditure.

While a slow session on an empty stomach allows you to primarily consume reserve fats, its low intensity requires little time to recover.

While a slow session on an empty stomach allows you to primarily consume reserve fats, its low intensity requires little time to recover. Indeed, after an effort, the body's basic metabolism increases to meet its needs. It therefore consumes more calories, even at rest, during the recovery phase. While a long and/or intense session carried out during the day primarily consumes glycogen reserves, the recovery phase significantly increases the basic metabolism, even more than a session at a moderate pace and of average duration. The advantagestagFasting sessions for weight loss are therefore not so obvious in purely accounting terms.

On the other hand, we should not neglect the digestive comfort associated with a session of this type, and the very pleasant sensations that go with it. An asset appreciated by many cyclists and triathletes, who nevertheless take care to carry the necessary carbohydrate supplies to limit the risks of a sudden drop in performance during the session.

A method to improve endurance

Exercising on an empty stomach with limited glycogen stores involves the implementation of adaptation systems, because the body then faces a difficult situation. Deprived of sugars or almost, it must function with fatty acids as fuel, less efficient and therefore with a lower yield.. A state substantially equivalent to that encountered at the end of long-distance events, such as the marathon and its famous "wall" at the 30th km, when glycogen reserves are exhausted, but it is still necessary to maintain a certain intensity of effort to go to the end without seeing performance drop dramatically.

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Fasting sessions therefore allow the body to be confronted with this phenomenon, and to put back in place the adaptive processes that it has assimilated during the tests. More surprisingly, Exercising on an empty stomach trains the body to resynthesize the low glycogen reserves in the muscles, and therefore increases their capacity to store it.. And when the reserves are full, this additional storage capacity ensures a few extra minutes at full output.

Disadvantages and precautions

You should not conduct a fasted session in the same way as a daytime session. First in terms of intensity. Because your glycogen reserves are limited, you risk failure. But first of all, you must start by drinking at least a large glass of water. Water is essential for the body to function, and the risks of dehydration are real after a night of fasting.. With the possibility of joint or tendon injuries as a result.

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Then you adapt your pace, avoiding any unevenness. When lacking sugars, the body goes into reserve mode, and To burn fat faster, it is better to aim for an intensity that corresponds to the priority consumption of fat, therefore around 60 to 70% of maximum capacity, no more. Too fast a pace, or worse, a session of interval training not only quickly empties the low glycogen reserves, but also risks using proteins as a substitute substrate, which form the very structure of the muscles. Proteins are only made available to produce energy as a last resort. The cellular damage is major and we then speak of "hitting the muscle", which of course turns out to be totally unproductive in addition to causing very bad muscle aches.

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Finally, the duration of the effort should be between 40 and 60 minutes running or swimming, and up to 2 hours maximum pedaling (because cycling is a supported sport and there may be moments of freewheeling). Enough to provoke the desired adaptation processes, and not too much so as not to tire the body excessively. Carrying an energy gel or fruit paste with you can provide some insurance in case of a real craving.. You should drink if possible (not easy when running or swimming), but more surely as soon as you get back, before the real breakfast or the real evening meal which you should not skip in order to reconto establish the reserves.

Above all reserved for experienced athletes for a simple question of effort management, the fasted session should not be repeated more than three times a week. It depends on your general physical condition and the need to keep qualitative sessions in addition to progress. It is therefore a question ofa relatively easy training method to implement, but from which you should not expect miracles.

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