Fatmax is the intensity at which fat burning, measured in grams per minute, is at its highest. For many it occurs at moderate intensity, often around 45-65% of maximum oxygen uptake (VO₂max), although there is large variation between individuals.

Does very easy training burn the most fat?

No. At low intensity the total energy expenditure is also lower. Fat burning usually increases as intensity rises from low to moderate, and then decreases at higher intensity.

Do I need carbohydrates during a one-hour session?

For sessions lasting around one hour or less, it is usually not necessary to take in carbohydrates during the session.

What should I eat before a long or demanding session?

A meal rich in carbohydrates such as oats, bread, rice, pasta, potatoes or fruit. A larger meal usually suits a few hours before training, while a banana or sandwich may be better when there is less time.

Why does fat burning increase during long sessions?

Glycogen stores gradually decrease during long sessions, so over time a larger portion of the energy can come from fat, especially at moderate intensity.

Fat Burning During Endurance Training – What You Should Know | Hardworkout Magazine

Key takeaways

- Fat is the main energy source at low and moderate intensity, while carbohydrates supply a growing share of the energy as intensity rises.

- Fatmax – the intensity at which fat burning per minute peaks – occurs for many at around 45-65% of VO₂max, but varies considerably between individuals.

- Regular endurance training increases the number of mitochondria, the activity of fat-breakdown enzymes and the transport of fatty acids into muscle cells, so a trained athlete burns more fat at the same speed or power than an untrained one.

- Sessions of about 1-2.5 hours may call for 30-60 grams of carbohydrates per hour, while sessions of roughly an hour or less usually need none.

- Better fat utilisation spares glycogen, leaving more carbohydrate available later in a session or race.

Why does the body rely on fat during endurance training?

If you are engaged in endurance training, your muscles need a steady supply of energy over a longer period. Fat plays an important role, and the body has far greater energy stores in the form of fat than it has stored as carbohydrates.

Regular endurance training affects how the body retrieves energy from these stores and can make the muscles better at using fat.

In short

Fat is an important energy source during endurance training, especially at low and moderate intensity.

Fat is broken down into fatty acids that the muscles can use to produce energy.

As intensity increases, the body derives a larger portion of its energy from carbohydrates.

Fatmax is the intensity at which fat burning measured in grams per minute is at its highest.

During long sessions, more of the energy can come from fat as glycogen stores decrease.

Regular endurance training makes the muscles better at using fat as an energy source.

Easy and longer sessions at moderate intensity contribute to the adaptations that improve fat burning.

Carbohydrates are still important, especially before and during long or hard training sessions.

How does the body turn fat into usable energy?

Fat is primarily stored as triglycerides in adipose tissue, but smaller amounts are also found in the muscles.

When energy needs increase, triglycerides are broken down to release fatty acids. The fatty acids can then be taken up by muscle cells and broken down in the mitochondria through beta-oxidation.

This breakdown is part of the processes that form ATP, which the muscles need to contract.

Fat contains a lot of energy, but the body cannot release energy from fat as quickly as from carbohydrates.

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At what intensity do you burn the most fat?

At low and moderate intensity, fat can cover a large part of the energy needs. As intensity increases, an increasingly larger share of the energy comes from carbohydrates.

Very easy training does not necessarily yield the highest fat burning per minute. At low intensity, the total energy expenditure is also lower. Fat burning usually increases when intensity rises from low to moderate, before it decreases at higher intensity.

The intensity at which fat burning measured in grams per minute is highest is called Fatmax.

For many, this occurs at moderate intensity, often around 45-65% of maximum oxygen uptake (VO₂max), but there is a large variation between individuals. Well-trained endurance athletes may experience the highest fat burning at higher intensities than less trained individuals.

![](https://hardworkout.no/wp-content/uploads/2018/08/AdobeStock191303819.jpeg)

What happens to fat burning during a long session?

During long training sessions, glycogen stores gradually decrease. Over time, a larger portion of the energy can come from fat, especially when maintaining moderate intensity.

The amount of glycogen that can be stored in muscles and the liver is limited. When the muscles derive more energy from fat, glycogen stores are emptied more slowly. Thus, more glycogen is available later in the session or competition.

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How does training make the muscles better at burning fat?

Regular endurance training leads to several changes in the muscles.

Among other things, the number of mitochondria and the capacity to produce energy aerobically increases. The activity of enzymes involved in fat breakdown also increases, while the transport of fatty acids into muscle cells and mitochondria becomes more efficient.

A well-trained endurance athlete can therefore burn more fat at the same running speed or power on a bike than a less trained person. Fat can also cover a larger part of the energy needs at higher intensities.

Easy and longer sessions at moderate intensity contribute to these adaptations.

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How many carbohydrates do you need before and during a session?

Even though endurance training makes the muscles better at using fat, carbohydrates are still important. The need is particularly high before and during long or hard sessions.

Before long or demanding sessions, it is therefore wise to eat a meal rich in carbohydrates. Oats, bread, rice, pasta, potatoes, and fruits are good sources. A larger meal is usually suitable a few hours before training, while, for example, a banana or sandwich may be appropriate when there is less time before the session.

For sessions lasting around one hour or less, it is usually not necessary to add carbohydrates during the session.

For sessions lasting about 1-2.5 hours, 30-60 grams of carbohydrates per hour may be relevant. In very long sessions and competitions, the need may be higher.

Sports drinks, energy gels, bananas, and other easily digestible foods can be used during the session. How much you can tolerate varies, so both the amount and type of carbohydrates should be tested during training before competition.

![Carbohydrates during training Endurance training](https://hardworkout.no/wp-content/uploads/2026/08/ChatGPT-Image-16.-aug.-2026-110230.png)

Sources:

Regulation of Energy Substrate Metabolism in Endurance Exercise – [International Journal of Environmental Research and Public Health](https://www.mdpi.com/1660-4601/18/9/4963)

New Horizons in Carbohydrate Research and Application for Endurance Athletes – [Springer Nature Link](https://link.springer.com/article/10.1007/s40279-022-01757-1)