The notion that exercise is merely a means to build muscle is a gross oversimplification. While it is true that physical activity strengthens muscles, its impact extends far beyond the confines of our limbs. In fact, exercise acts as a biological necessity, akin to breathing or eating, and its absence can be as detrimental to our health as a sedentary lifestyle. This is because our muscles function as an endocrine organ, releasing a myriad of molecules known as myokines and exerkines that influence every system in our bodies. These substances, like hormones, communicate via the bloodstream with various organs, from the brain to the immune system, and even the skeleton.
One of the most widely studied myokines is interleukin-6 (IL-6). While it is released at rest, its levels skyrocket during high-intensity or aerobic endurance exercise. Irisin, another key player, maintains body fat balance, while brain-derived neurotrophic factor (BDNF) is involved in neuroplasticity and cognitive function. Exercise also stimulates the release of exerkines, which play a crucial role in cardiovascular, metabolic, immune, and neurological health.
The impact of exercise on the immune system is particularly noteworthy. Recent publications identify at least nine myokines that influence the proper functioning of the immune system, including irisin, decorin, and the interleukins IL-6, IL-7, and IL-15. These myokines promote the proliferation and differentiation of immune cells, enhancing immune surveillance and reducing chronic systemic inflammation. For instance, IL-6 acts as an anti-inflammatory signal, regulating the activity of lymphocytes, macrophages, and NK cells.
Exercise also has a profound effect on the nervous and neurocognitive system. Muscle exerts a direct influence on the brain via the 'muscle-brain axis'. Molecules like BDNF, irisin, and cathepsin B stimulate the formation of new neurons and are linked to improved learning and memory. Irisin, for instance, has been linked to increased levels of BDNF in the hippocampus, a region crucial for memory. Cathepsin B contributes to neuronal regeneration and improved cognition.
Furthermore, exercise plays a pivotal role in glucose and fat metabolism. During exercise, IL-6 mobilizes fatty acids from adipose tissue, primarily visceral fat, promoting fat burning and helping maintain blood glucose levels. It also regulates insulin sensitivity, enabling the muscle to take up glucose more efficiently, which explains some of the benefits of exercise in preventing type 2 diabetes.
In the cardiovascular system, physical activity triggers the release of exerkines, which promote vasodilation, improve vascular function, and reduce arterial stiffness. This explains why physically active people have a lower risk of high blood pressure, coronary heart disease, and heart failure.
Exercise also has a significant impact on bones and osteoporosis. Multiple myokines promote bone formation and remodeling by stimulating the activity of osteoblasts and regulating bone mineral density. This is a necessary complement to the mechanical stresses of exercise, and to prevent and combat osteoporosis.
Lastly, exercise has been linked to tumor suppression and reduced cancer risk. An article published in The Lancet Oncology identifies a sedentary lifestyle as a risk factor for more than 10 types of cancer. This is partly explained by the fact that during exercise, myokines are released, which inhibit the spread of cancer cells and reduce DNA damage from potentially malignant cells. Exercise also mobilizes immune cells capable of recognizing and destroying tumor cells in the early stages of growth.
In conclusion, the impact of exercise on our bodies is far more profound than initially thought. Our muscles, acting as an endocrine organ, release a myriad of molecules that influence every system in our bodies, from the immune system to the cardiovascular system. Exercise is, therefore, not just about building muscle; it is a biological necessity that promotes overall health and well-being.
