Most people are aware today that physical inactivity is related to the manifestation of chronic diseases, which significantly modify the quality and prognosis of life in a negative way. There are many benefits to be gained from regular exercise.
Muscle is the largest organ in the body representing about 40% of body mass in non-obese males. We tend to think of muscles as enabling locomotion of the body, and playing a role in regulating energy and metabolic processes. However muscle is also a secretory organ capable of producing molecules with vital functions to support homeostasis, our health, and to help with aging.
There is gradual loss of skeletal muscle mass and function as we age. Physically inactive people can lose as much as 3% to 5% of their muscle mass each decade after age 30. Even if we are active, we can still have some muscle loss.
In research and clinical practice, loss of muscle mass is recognized as one of the main factors leading to negative health outcomes in geriatric disease, contributing to chronic inflammation, hormonal alterations, and vascular dysfunction. Muscle has been referred to as the organ of longevity.
When exercising and using the muscles under load or with resistance training, muscles release hundreds of different signaling proteins within the muscle cells called myokines (cytokines produced by myocytes). The signals may be to itself or the same cell (autocrine), nearby cells (paracrine), and to faraway organs (endocrine). Their role includes sending signals to initiate or help with repair and regeneration of muscle, hypertrophy, and uptake of glucose into muscle tissue.
Another very important characteristic and role of some myokines is that they travel outside of the muscle tissue, enter the blood stream and circulate throughout the body. Those myokines send signals to other organs, including fat cells, liver, pancreas, bone, bone marrow, heart, white blood cells, immune cells, brain cells, and even stem cells. Those signals have the ability to regulate the metabolic and physiological response in the other organs and to reduce inflammation. They are also instrumental in tissue regeneration and repair, maintenance of healthy bodily functioning, anti-obesity and immunomodulation, cancer prevention, heat generation, tissue and blood vessel repair, possible heart muscle repair to patients with previous heart attacks, better diabetes control, and potential treatment of cancer.
Exercise improves clinical outcomes in patients with cancer. Preclinical studies suggest the involvement of myokines in exercise-induced tumor suppression through decreasing cancer cell proliferation, limiting migration and increasing apoptosis (the process of programmed cell death). There are many different types of myokines. Those commonly identified include interleukin-6 (IL-6), IL-8, IL-15, irisin, myostatin, fibroblast growth factor 21 (FGF21), leukemia inhibitory factor (LIF), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor-1 (IGF-1). Their beneficial effects can be seen in this diagram.