Physical activity is widely recognized for its health benefits, but the precise molecular reasons have long been a complex puzzle. Scientists are now uncovering a class of signaling molecules called exerkines, which are released into the bloodstream during and after physical exertion. These molecules function as messengers, carrying instructions from the tissues engaged in exercise to distant parts of the body. This helps explain how an activity like running, which primarily involves the legs, can produce positive effects in organs such as the brain or liver.
The Sources of Exerkines
The term “exerkine” is a broad classification for molecules released in response to exercise, and they originate from a multitude of tissues. This widespread production shows that physical activity initiates a systemic, body-wide biological conversation, with many different organs and cell types participating.
Skeletal muscle is the most well-known source, and the exerkines it produces are called myokines. When muscles contract during a workout, they release these protein-based signals into circulation. One of the first molecules identified was Interleukin-6 (IL-6), which plays a part in metabolic regulation and inflammatory responses. This discovery shifted the understanding of muscle from a purely mechanical tissue to an active endocrine organ.
Beyond muscle, adipose tissue (body fat) is another contributor, releasing signals known as adipokines. Exercise stimulates fat cells to alter their secretory profile, influencing energy metabolism and inflammation. The liver also produces hepatokines to manage glucose and fatty acid metabolism. Immune cells, neurons, and cells within the heart also release their own exerkines, contributing to the signaling network that coordinates the body’s adaptation to exercise.
Systemic Effects of Exerkines
The messages from exerkines trigger a wide array of physiological changes, impacting the health of multiple organ systems. These molecules are how the body adapts and becomes more resilient through regular physical activity. Their influence extends from energy management to brain function, showing the interconnected benefits of exercise.
A primary area of influence for exerkines is metabolic health. They improve insulin sensitivity, which allows cells to more effectively take up glucose from the bloodstream for fuel. For instance, the myokine irisin promotes the browning of white adipose tissue, a process that increases energy expenditure. Others stimulate lipolysis, the breakdown of stored fats into fatty acids that can be used for energy.
Exerkines also impact brain and cognitive function. Some molecules, like Brain-Derived Neurotrophic Factor (BDNF), can cross the blood-brain barrier. Once in the brain, BDNF supports neurogenesis (the growth of new neurons) and strengthens connections between existing ones. This enhances learning, improves memory, and may offer protection against age-related cognitive decline.
Cardiovascular and immune functions are also modulated by exerkines. In the cardiovascular system, they help regulate blood pressure and promote angiogenesis, the formation of new blood vessels, which improves blood flow. Many exerkines also have anti-inflammatory effects. While exercise causes a temporary inflammatory response, exerkines help manage this, contributing to lower chronic inflammation, a known factor in many long-term diseases.
How Different Exercises Influence Exerkine Production
The type, intensity, and duration of physical activity influence the profile of exerkines released. Different forms of exercise create distinct physiological demands, prompting tissues to secrete unique combinations of these molecules. This means a varied fitness routine can provide a broader range of health benefits by stimulating a more diverse exerkine response.
Endurance exercises, such as jogging or cycling, are effective at stimulating exerkines that benefit metabolic and cardiovascular health. The sustained effort of aerobic activity promotes the secretion of molecules that improve fat oxidation and overall metabolic efficiency. This makes endurance training a good way to strengthen the heart and circulatory system.
Resistance training like weightlifting primarily stimulates the release of myokines geared toward muscle health. These signals promote muscle protein synthesis, which is the process of repairing and rebuilding muscle fibers to become stronger. The mechanical stress placed on muscles during resistance exercise is a trigger for this growth-oriented response.
High-Intensity Interval Training (HIIT), which involves short bursts of effort followed by brief recovery, triggers a broad release of exerkines. The intense metabolic stress of HIIT is a stimulus for the secretion of molecules that affect multiple systems, including BDNF for brain health. A fitness regimen that incorporates endurance, resistance, and high-intensity work is the most effective strategy for stimulating a comprehensive exerkine profile.