Myokines are small proteins or peptides released by skeletal muscle cells in response to muscular contractions. These molecules act as signaling messengers, enabling muscles to communicate with various other organs throughout the body. This highlights skeletal muscle as an active endocrine organ, influencing systemic health through a sophisticated communication network.
The Release of Myokines Through Exercise
Physical activity is the primary stimulus for myokine production and release. When muscle fibers contract during exercise, they secrete these signaling molecules. Both aerobic activities, such as running or cycling, and resistance training, like weightlifting, effectively trigger this release. The specific types and quantities of myokines released can vary depending on the intensity, duration, and type of muscle contraction involved.
A single session of exercise leads to an immediate increase in myokine levels, which typically return to baseline within a few hours to a day. This transient increase demonstrates the direct link between muscular engagement and myokine secretion.
Myokines and Organ Communication
Once released from muscle cells, myokines enter the bloodstream and travel throughout the body as systemic signaling molecules. They act as messengers, allowing muscles to communicate with distant organs. This extensive communication network involves various target organs, including the liver, adipose (fat) tissue, pancreas, bones, brain, heart, gut, vascular bed, and skin.
The presence of receptors for myokines on cells across these diverse organs underscores their role in orchestrating whole-body responses to physical activity. This muscle-organ crosstalk is a fundamental mechanism by which exercise imparts its beneficial effects on overall health.
Metabolic and Anti-inflammatory Functions
Myokines play a significant role in regulating the body’s metabolism. They contribute to improved insulin sensitivity, helping cells more effectively take up glucose from the bloodstream and assisting in blood sugar regulation. Myokines also promote the breakdown of fats, a process known as lipolysis, and can induce the “browning” of white adipose tissue. This browning effect increases energy expenditure by turning energy-storing white fat cells into more metabolically active, heat-generating brown-like fat cells. Specific myokines like irisin and fibroblast growth factor 21 (FGF-21) are involved in these metabolic adaptations.
Beyond their metabolic roles, myokines exert anti-inflammatory effects. Exercise-induced myokines help counteract chronic low-grade inflammation, a state often associated with many long-term health conditions. Interleukin-6 (IL-6), released during muscle contraction, stimulates the production of anti-inflammatory cytokines and inhibits pro-inflammatory factors like tumor necrosis factor (TNF), contributing to a systemic anti-inflammatory environment in the body.
Impact on Brain and Bone Health
Myokines significantly influence brain health, with certain molecules capable of crossing the blood-brain barrier. Brain-Derived Neurotrophic Factor (BDNF) supports the growth and survival of neurons, enhances neuroplasticity, and is linked to improved mood and cognitive functions. Myokines like irisin and cathepsin B are released into circulation during exercise and can cross into the brain to promote BDNF expression, contributing to the observed cognitive benefits of physical activity.
Myokines also play a role in maintaining bone density and strength. They signal to various bone cells, influencing both bone formation and the reduction of bone resorption. Specific myokines, including irisin and IL-6, modulate bone metabolism. This signaling helps to preserve skeletal integrity, highlighting another way that muscle activity contributes to the health and resilience of other bodily systems.