Doing more hours of treadmill does not guarantee losing more fat, and the culprit is our metabolism

There is a deep-rooted belief in the world of sports that treats the human body as if it were a simple thermal calculator, which leads us to think that if half an hour of cardio burns 300 calories, a full hour will burn 600. At the end of the day, it all boils down to ‘the more, the better’, but biology and metabolism are much more complex than a linear mathematical equation.

It is studied. To get out of this thought that can be logical, an article published this same year made a comparison between the traditional additive model and the “constrained” model of energy expenditure.

In this way, when subjecting different individuals to a type of aerobic exercise such as running, the increase in daily energy expenditure was only 30% of what would be expected if the model were completely linear. That is, instead of adding all the calories burned on the treadmill to the total expenditure for the day, the human metabolism implements a partial compensation.

Because? This discrepancy occurs because the body, faced with an acute caloric deficit induced by prolonged exercise, activates a series of biological energy-saving mechanisms to protect its energy reserves, still aware of its need for survival. That is, far from burning energy without limit, the body “cuts” spending on other functions.

For example, we know that metabolism, when we are on the treadmill, can slow down slightly, reducing the energy it ‘sends’ to non-urgent physiological processes in response to the stress of very aggressive training.

There is more. A 2023 review concludes that decreasing unstructured physical activity is an incredibly common coping mechanism. This means that when a very demanding workout begins, people unconsciously tend to move less the rest of the day, which again significantly reduces the total caloric deficit.

But when we are persistent in doing intense training, the body ends up adapting and becoming much more efficient, making the neuromuscular and cardiovascular system need less energy to do the same mechanical work. And here again we see that more exercise is not always more expense.

Variability. Not all humans are the same, partly due to this great complexity of our organism. We see this in a review which determined that the average energy compensation after the introduction of exercise is around 18%, but warned of strong heterogeneity. The degree to which our body “boycotts” extra caloric expenditure depends strongly on variables such as the duration of exercise, genetics and, above all, the amount of adipose tissue that a person has when starting treatment.

Here, a 12-week study in overweight adults pointed to how different groups showed radically different levels of metabolic compensation, registering 35% in one group compared to a massive 63% in the other. But what is clear is that doing more hours on the elliptical or treadmill does not guarantee a parallel increase in the loss of fat mass.

Cardio works. Exercise continues to be a non-negotiable pillar due to its profound benefits on cardiometabolic health and continues to contribute to the loss of body fat. What science tells us is that there is a law of diminishing returns that stipulates that, above a certain threshold, adding more training volume generates a decreasing net caloric impact.

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