Muscle functions as an endocrine organ, releasing signaling molecules called myokines during contraction. These molecules influence multiple physiological systems. The article summarizes current scientific understanding of myokines and exerkines.
Background
- The discovery of myokines transformed physiology, leading to the idea that exercise is medicine.
- A 2024 review identified myokines as the reason exercise benefits the immune system.
- Interleukin-6 (IL-6) is the most studied myokine; levels can increase up to 100-fold during intense exercise. Other notable myokines include irisin and brain-derived neurotrophic factor (BDNF).
- Exercise also stimulates release of exerkines from other organs; a 2022 review highlighted their roles in cardiovascular, metabolic, immune, and neurological health.
- Physical inactivity correlates with increased risk of disease and all-cause mortality.
Effects on Specific Systems
Immune System
- At least nine myokines (e.g., irisin, decorin, IL-6, IL-7, IL-15) influence immune function.
- They promote immune cell proliferation and differentiation, enhancing immune surveillance.
- They reduce chronic systemic inflammation. IL-6 acts as an anti-inflammatory signal regulating lymphocytes, macrophages, and NK cells.
Nervous and Neurocognitive System
- The "muscle-brain axis" describes direct muscle influence on the brain.
- Molecules such as BDNF, irisin, and cathepsin B stimulate neurogenesis, improve learning and memory, and protect against cognitive decline.
- Irisin is linked to increased BDNF in the hippocampus; cathepsin B contributes to neuronal regeneration.
Glucose and Fat Metabolism
- During exercise, IL-6 mobilizes fatty acids from adipose tissue (especially visceral fat), promoting fat burning and maintaining blood glucose.
- IL-6 regulates insulin sensitivity, improving glucose uptake by muscle.
- Muscle acts as a "metabolic thermostat" regulating energy expenditure.
Cardiovascular System
- Physical activity triggers exerkines that promote vasodilation, improve vascular function, and reduce arterial stiffness.
- Active individuals have lower risk of hypertension, coronary heart disease, and heart failure.
- Exercise for cardiac patients should be prescribed by a healthcare professional.
Bones and Osteoporosis
- Multiple myokines promote bone formation and remodeling by stimulating osteoblast activity and regulating bone mineral density.
- This complements mechanical stress from exercise in preventing osteoporosis.
Tumor Suppression and Cancer Risk
- A study in The Lancet Oncology identified sedentary lifestyle as a risk factor for over 10 cancer types.
- Myokines released during exercise can inhibit cancer cell spread and reduce DNA damage.
- Exercise mobilizes immune cells that recognize and destroy tumor cells.
- Even a single exercise session increases levels of myokines that suppress cancer cell growth.
Summary
Every muscle contraction sends signals that regulate internal balance, making movement biologically necessary for proper system function.