It is tempting to understand muscle’s role in the body as a simple mechanical motor. But the truth is much more complex: our muscles function as an endocrine organ that can influence virtually every system in our bodies.

When a muscle contracts, hundreds of molecules known as myokines – substances essential for the body to function properly – are released. Their discovery transformed modern physiology, giving rise to the idea that “exercise is medicine”.

But this concept falls short. In reality we can go much further, and say that exercise is as necessary for our health as breathing or eating, while a sedentary lifestyle and lack of movement can be classified as a source of illness.

Myokines are hormones that communicate via the bloodstream with various organs such as the brain, adipose tissue, liver, bone and the immune system. According to a 2024 review, they are the reason why exercise is beneficial for the immune system.

The most widely studied myokine to date is interleukin-6 (IL)-6. While it is released at rest, it is released at levels up to 100 times higher during high-intensity or aerobic endurance exercise. Also of importance are irisin, which is key to maintaining body fat balance, and brain-derived neurotrophic factor (BDNF), which is involved in neuroplasticity and cognitive function.

Exercise also stimulates other organs to release exerkines, which are equally important. A 2022 review revealed the role that these molecules play in cardiovascular, metabolic, immune and neurological health. If we are inactive – meaning few exerkines circulate in our bodies – the risk of disease and all-cause mortality increases.

Molecules that benefit the entire body

Myokines act in different ways in different parts of the body:

Immune system: Recent publications identify at least nine myokines that influence the proper functioning of the immune system. These include irisin, decorin and the interleukins IL-6, IL-7 and IL-15. Their release during exercise promotes the proliferation and differentiation of our immune cells, enhancing immune surveillance. They also reduce chronic systemic inflammation, a key factor in preventing many metabolic and cardiovascular diseases. IL-6, for example, acts as an anti-inflammatory signal that can regulate the activity of lymphocytes, macrophages........

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