Bike training during fasting

Bike training during fasting? This is one of those recurring themes among us cyclists.

Is it useful or not? Are there any contraindications?

So, let’s try to clear things up.

First, it is useful to divide fasting exercises into two categories.

The first is those who do fasting to lose weight and improve fat metabolism.

The second is for those who do fasting out of “need”, that is, lack of time: if you can train from 6 to 8 in the morning it will be difficult to leave having digested a good breakfast.


Let’s start with those who train on an empty stomach to stimulate the body to use fats more effectively as fuel, along with sugars. It is a training that is highly valued by both professionals and amateurs.

Let’s not kid ourselves this is a great way to lose a few pounds: it consumes the fat deposited inside the body instead of the one ingested.

For athletes of a certain level, who obviously do not need to lose excess weight, it serves to improve the ability to use fat as fuel, but not only this, but it is also a very good way to increase endurance and performance over long distances.

What does the science say? One gram of fat contains 9 kilocalories, while carbohydrates contain about 4. Therefore, for the same weight, fats provide more energy. It is also fair to add that muscle and liver glycogen reserves are exhausted in about two hours (depending on the intensity of the effort), while fat reserves are practically inexhaustible.

How to train?

For good results it is necessary to start training with low blood sugar and reduced glycogen reserves. This means that if you’ve had pasta or pizza or desserts the night before, it’s unlikely that the results will be as expected. In contrast, a protein-based dinner is ideal.

The ride must be made on an empty stomach.

Intensity and duration

Fats are only used by the body when the intensity of the effort is medium to low. In technical jargon this translates to 70/75% of the Max. CF and no more than the CF of the middle power zone or Z3.

Higher intensity training requires sugar. But if sugars are scarce, the body will produce them by destroying muscle proteins through the gluconeogenesis mechanism (process of glucose synthesis from non-glycidic precursors). For this reason, high-intensity fasting training can endanger the condition of the muscles.

It’s a stressful workout for our bodies, so the advice is not to include it in your routine more than once or twice a week.

As for the duration, if you are new to this training, you will not have to exceed 1h30’/2h. As your body gets used to it, you may even be able to go beyond 3 hours. In this case, however, it is important to eat something after 1h30′, as you would do on a traditional outing, preferring carbohydrates with a low glycemic index.


Some people train first thing in the morning because they prefer it, others do it for work and family commitments. In this case, of course, that means cycling without having digested breakfast.

If you are training at a low intensity, you can safely use the advice given in the previous point.

If, on the other hand, the programme foresees high intensities, then the focus must be changed completely.

In this case it will be necessary to replenish the muscle and liver glycogen supplies the night before. How? With a good carbs dinner, for example.

This way your blood sugar level in the morning won’t be so low and you’ll be able to train well for at least an hour and a half.

If you plan a longer workout, then you’ll need to plan your diet well: at breakfast as well as at workout, liquid and rapidly-assimilated carbohydrates are perfect.


In both cases, you will return home with your glycogen supply either completely or nearly empty. Therefore, breakfast (or lunch for those who have trained long distance) should be rich in carbohydrates. But it is also important to include fats and proteins to have the necessary amino acids for protein synthesis after training.

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Stefano Francescutti

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