Do muscles turn into fat when we stop stimulating them with exercise?

The belief that muscle turns into fat when a person stops exercising is one of the most widespread misconceptions in the fitness world.

However, this claim is false. According to various specialized sources, including Trinity Health System, Fit&Well, and Abbott, muscle and fat are completely different tissues , and one cannot be converted into the other.

When a person interrupts their training routine, their muscles begin to undergo a process called atrophy . This means that, without stimulation, the muscles decrease in size and strength.

'Fit&Well' explains that this phenomenon occurs because the body no longer needs to maintain unused muscle tissue, leading to its progressive deterioration.

At the same time, decreased physical activity means lower daily energy expenditure. If caloric intake remains the same—that is, if you continue eating as you did when you were training regularly—excess energy tends to be stored as body fat.

This combination of muscle loss and fat gain can give the impression that the muscle has been transformed into fat , although this is not the case from a biological point of view.

Trinity Health System clarifies that this misperception is due to visible physical changes: “This is more about transformations in your body than a direct conversion of one tissue into another,” the medical entity notes.

Stopping exercise can cause changes in your body in a matter of days. According to Abbott, in the first week without activity, you can see increases in resting heart rate and loss of endurance.

From that moment on, muscles begin to shrink, and the risk of weight gain increases. In the long term, a sedentary lifestyle can contribute to the development of diseases such as type 2 diabetes, cardiovascular disease, and even a shorter life expectancy.

'Fit&Well' supports this perspective with data from studies such as one published in the International Journal of Obesity, which confirms the direct relationship between lower energy expenditure and increased adipose tissue.

Even if you stop going to the gym, there are ways to maintain muscle mass through bodyweight exercises, such as push-ups, squats, and pull-ups. It's also essential to adjust your diet to your new activity level to avoid calorie excess.

For those who lead a sedentary lifestyle, Abbott recommends incorporating at least 30 minutes of moderate physical activity five times a week. Even brisk walking or mobility exercises can be beneficial.

Evidence indicates that the negative effects of a sedentary lifestyle can be reversed with the sustained adoption of an active routine.

The myth that muscle turns into fat when you stop exercising has no scientific basis . What actually happens is a decrease in muscle tissue due to lack of use and an increase in body fat if your diet isn't adjusted to the lower energy demand.

To maintain a healthy body composition, it is essential to maintain regular physical activity and adapt eating habits to the level of exercise.

*This content was written with the assistance of artificial intelligence, based on publicly available information released to media outlets. It was also reviewed by a journalist and an editor.

DIGITAL REACH EDITORIAL