Myokines: How Your Muscles Talk to Your Brain, Bones, and Immune System (2026)

Your muscles are not just mechanical actuators. They are a secretory organ – the largest in the human body by mass – and every time they contract, they release a cascade of signaling molecules into your bloodstream that talk to your brain, your bones, your liver, your fat tissue, your immune system, and your gut.

These molecules are called myokines (from Greek myo-, meaning muscle, and -kine, meaning to move or signal), and their discovery over the past two decades has fundamentally restructured how exercise scientists, immunologists, and aging researchers think about physical activity. Exercise does not work because it "burns calories" or "gets your heart rate up." Exercise works because it triggers your largest organ to broadcast a molecular signal that recalibrates inflammation, metabolism, neuroplasticity, and immune surveillance across your entire body.

When you stop moving, that signal goes silent. The downstream consequences – chronic inflammation, cognitive decline, metabolic dysfunction, impaired immune function – are not coincidences. They are the predictable result of losing the myokine communication network that a sedentary body no longer produces.

This article covers the major myokines with established human evidence, how they work, why they decline with age and inactivity, and what it takes to keep the signal strong.

TL;DR – Key Takeaways

• Skeletal muscle (40% of body mass) is the largest endocrine organ, secreting 600+ myokines during contraction
• IL-6 from muscle is anti-inflammatory – the opposite of IL-6 from immune cells (the "IL-6 paradox")
• Irisin (Bostrom 2012, Nature) converts white fat to calorie-burning beige fat and upregulates BDNF in the brain
• BDNF is the primary mediator of exercise-induced neuroplasticity, memory enhancement, and resistance to neurodegeneration
• IL-15 from muscle activates natural killer cells – directly linking exercise to cancer immune surveillance
• SPARC suppresses colon cancer cell proliferation; meteorin-like drives anti-inflammatory immune responses
• Myokine secretion declines with age and sedentary behavior – sedentary aging = losing an endocrine organ
• Resistance training and high-intensity exercise are the most potent myokine triggers
• No pill replicates the full myokine profile of exercise – this is why "exercise in a bottle" does not exist

The Discovery: When Muscles Became an Endocrine Organ

The story begins in 2000, when Bente Klarlund Pedersen and her team at the University of Copenhagen observed something unexpected: interleukin-6 (IL-6), a molecule primarily known as a pro-inflammatory cytokine (a small protein released by cells that affects the behavior of other cells, particularly immune cells), was being released in enormous quantities from contracting skeletal muscle during exercise – but the exercising individuals were not inflamed.

The IL-6 levels in exercising subjects rose 100-fold above resting levels during prolonged exercise (Pedersen et al., 2001, The Journal of Physiology). This was puzzling. IL-6 was supposed to be a bad guy – elevated in obesity, type 2 diabetes, rheumatoid arthritis, and sepsis. Why was vigorous exercise – unambiguously healthy – flooding the body with it?

The answer, published over a series of papers culminating in a landmark 2003 review (Pedersen et al., 2003, The Journal of Physiology), was that muscle-derived IL-6 is fundamentally different from immune-cell-derived IL-6. Same molecule, different context, opposite effects. Pedersen coined the term "myokine" to describe IL-6 and other cytokines released by contracting muscle, establishing skeletal muscle as a bona fide endocrine organ.

By 2016, proteomic (the large-scale study of proteins produced by an organism) analyses had identified over 600 myokines released by skeletal muscle (Whitham & Febbraio, 2016, Trends in Endocrinology and Metabolism). Most have not been fully characterized. But the handful that have been studied in depth reveal a communication network of extraordinary complexity and importance.

The Major Myokines: A Field Guide

IL-6: The Paradox Molecule

IL-6 (interleukin-6) is the most abundant and best-studied myokine. Its story is a case study in why context matters more than the molecule itself.

When produced by immune cells and adipose tissue (fat): IL-6 is part of the chronic inflammatory milieu that drives atherosclerosis (buildup of plaques in artery walls), insulin resistance, neurodegeneration, and cancer. Chronically elevated IL-6 is a hallmark of inflammaging – see Inflammaging: The Silent Fire Accelerating How You Age.

When produced by contracting skeletal muscle: IL-6 acts as an anti-inflammatory signal. The mechanism: muscle-derived IL-6 stimulates the release of interleukin-1 receptor antagonist (IL-1ra) and interleukin-10 (IL-10) – both potent anti-inflammatory molecules – while simultaneously suppressing tumor necrosis factor alpha (TNF-alpha), one of the primary drivers of chronic inflammation (Pedersen & Febbraio, 2008, Physiological Reviews).

The difference is in the signaling pathway. Immune-cell IL-6 signals through a "trans-signaling" pathway via soluble IL-6 receptor – this is the inflammatory route. Muscle-derived IL-6 signals through "classic signaling" via membrane-bound IL-6 receptor – this is the anti-inflammatory, metabolic route (Rose-John, 2012, Biochimica et Biophysica Acta).

This is the IL-6 paradox: the same molecule can be either the fire or the fire extinguisher, depending on where it comes from and how it signals. The practical implication is profound – exercise does not just fail to worsen inflammation. It actively suppresses it through the very molecule that drives it in sedentary, chronically inflamed bodies.

The magnitude of the exercise IL-6 response is dose-dependent: larger muscle mass recruited and longer duration = more IL-6 released. A 45-minute resistance training session produces a moderate IL-6 spike; a 90-minute cycling session can increase IL-6 by 50-100 fold. In both cases, levels return to baseline within 1-2 hours, and the anti-inflammatory aftereffect persists for 24-72 hours.

Irisin: The Fat-Browning, Brain-Building Myokine

Irisin was identified in a 2012 Nature paper by Bostrom and colleagues at Harvard Medical School (Bostrom et al., 2012, Nature). The paper described irisin as a cleaved fragment of the membrane protein FNDC5, released by muscle during exercise, that drives the "browning" of white adipose tissue.

White adipose tissue (WAT) stores energy. Brown adipose tissue (BAT) and beige adipose tissue burn energy by converting calories directly into heat through the action of uncoupling protein 1 (UCP1 – a protein in mitochondria that uncouples the electron transport chain from ATP production, generating heat instead of stored energy). Irisin activates UCP1 expression in white fat cells, effectively converting them from storage units into furnaces. This process – called browning or beiging – increases metabolic rate, improves glucose tolerance, and reduces fat accumulation.

But irisin's story goes beyond fat. Subsequent research showed that irisin crosses the blood-brain barrier and directly upregulates BDNF expression in the hippocampus (the brain region critical for memory formation and spatial navigation) (Wrann et al., 2013, Cell Metabolism). This provided the first molecular mechanism linking muscle contraction to brain health – irisin is literally a messenger molecule that carries an exercise signal from your muscles to your neurons.

Andrew Huberman has discussed the irisin-BDNF pathway extensively as a key mechanism underlying the well-established cognitive benefits of exercise. His emphasis is on the directness of the link: it is not that exercise improves blood flow to the brain (though it does), or that it reduces stress (though it does). It is that contracting muscles secrete a specific molecule that travels through the blood, enters the brain, and turns on the gene for neuroplasticity. The molecule is irisin. The gene it activates produces BDNF.

Irisin levels decline with age and sedentary behavior. Huh et al. (2014, Metabolism, n = 117 healthy adults) found that circulating irisin levels were negatively correlated with age and positively correlated with muscle mass and physical activity. Translation: the less muscle you have and the less you move, the less irisin your body produces – and the less fat-browning and BDNF-boosting signal your brain receives.

BDNF: The Neuroplasticity Driver

Brain-derived neurotrophic factor (BDNF) is a protein that supports the survival, growth, and differentiation of neurons. It is the central mediator of exercise-induced cognitive benefits, and while it is primarily produced in the brain (particularly the hippocampus and cortex), its production is powerfully regulated by muscle-derived signals – primarily irisin and lactate (the byproduct of anaerobic metabolism during intense exercise).

Vaynman et al. (2004, Neuroscience) demonstrated that exercise-induced BDNF upregulation in the hippocampus was necessary for the cognitive benefits of exercise in rats – blocking BDNF abolished the memory improvements from running. In humans, Erickson et al. (2011, Proceedings of the National Academy of Sciences, n = 120 older adults, RCT) showed that one year of aerobic exercise increased hippocampal volume by 2% and increased serum BDNF levels, while the sedentary control group showed the expected 1-2% annual hippocampal shrinkage.

Rhonda Patrick has covered BDNF extensively in her research summaries, emphasizing that BDNF is not just about memory – it is about neuronal resilience. Higher BDNF levels are associated with resistance to Alzheimer's disease, Parkinson's disease, and age-related cognitive decline. Lower BDNF levels are associated with depression, anxiety, and accelerated brain aging. Exercise is the single most potent BDNF-boosting intervention available – more effective than any pharmaceutical currently approved.

The type of exercise matters for BDNF output:

• High-intensity exercise produces the largest acute BDNF spikes (Schmolesky et al., 2013, Physiology & Behavior)
• Resistance training increases BDNF through both irisin signaling and direct mechanical-metabolic pathways
• Zone 2 aerobic exercise (moderate-intensity sustained cardio) produces a smaller but more sustained BDNF elevation
• The combination of resistance and aerobic training produces the most robust long-term BDNF elevation

IL-15: The Immune System Activator

Interleukin-15 (IL-15) is a myokine with direct implications for cancer defense. IL-15 is a primary growth and activation factor for natural killer (NK) cells – immune cells that patrol the body and destroy virus-infected and cancerous cells without needing prior sensitization (they are part of the innate immune system, your body's first line of defense).

Nielsen et al. (2016, Cell Metabolism, n = mouse study with human exercise data) demonstrated that exercise-induced IL-15 mobilized NK cells into the bloodstream and redirected them to tumor sites, significantly reducing tumor growth and metastasis in multiple cancer models. The effect was abolished when NK cells were depleted, confirming that the anti-cancer effect of exercise was mediated through immune cell activation, not some other mechanism.

In humans, Pedersen et al. (2016, Cell Metabolism) showed that a single bout of exercise increased circulating NK cell numbers and cytotoxic (cell-killing) activity within minutes. Regular exercise training increased baseline NK cell function, suggesting a cumulative immune surveillance benefit.

The clinical implication: muscle mass and physical activity are not just correlates of lower cancer risk – they are mechanistic contributors to anti-cancer immune function, mediated in part through IL-15 signaling.

SPARC: The Colon Cancer Shield

SPARC (secreted protein acidic and rich in cysteine) is released by skeletal muscle during exercise and has been shown to suppress colon cancer cell proliferation. Aoi et al. (2013, Medicine and Science in Sports and Exercise) demonstrated that exercise-conditioned serum (blood serum collected after exercise, containing elevated SPARC) significantly inhibited colon cancer cell growth in vitro (in laboratory cell cultures), and that regular exercise in mice reduced colon tumorigenesis (the formation of tumors) in a SPARC-dependent manner.

This finding provides a molecular explanation for the well-established epidemiological association between physical activity and reduced colon cancer risk – an association that holds across dozens of studies and meta-analyses.

Meteorin-like (Metrnl): The Anti-Inflammatory Regulator

Meteorin-like (Metrnl) is a myokine identified by Rao et al. (2014, Cell, Harvard Medical School) that is induced by exercise and cold exposure. It promotes an anti-inflammatory immune response by stimulating the production of M2 macrophages (immune cells that resolve inflammation and promote tissue repair, as opposed to M1 macrophages that drive inflammation) and eosinophils (immune cells that, in this context, produce anti-inflammatory molecules).

Metrnl also enhances glucose tolerance and energy expenditure, adding to the metabolic benefits of the myokine cascade. Its dual role – anti-inflammatory and metabolic – exemplifies how muscle communicates with the immune system and the metabolic system simultaneously.

Key Takeaway: Irisin converts white fat to metabolically active brown fat and protects bone. IL-6 from exercise activates AMPK and promotes anti-inflammatory macrophage polarization. Brain-derived myokines (cathepsin B, BDNF) cross the blood-brain barrier and promote neuroplasticity. Muscle is not just a locomotion organ — it is an endocrine organ that broadcasts health-promoting signals throughout the body.

Myokine Decline With Age: Losing an Endocrine Organ

Here is the problem that makes all of this urgently relevant to aging: myokine secretion declines with both age and inactivity, and the two factors compound each other.

Age-Related Decline

As muscle mass decreases (sarcopenia – the progressive loss of skeletal muscle mass, strength, and function beginning around age 30), the total secretory capacity of the muscular endocrine organ shrinks. Fewer muscle fibers = fewer myokine-producing factories. Greiwe et al. (2001, American Journal of Physiology, n = 16 older vs. younger adults) showed that basal and exercise-stimulated IL-6 release from muscle was lower in older adults compared to younger adults, even when adjusted for muscle mass.

Irisin levels decline approximately 1-2% per year after age 40 (Huh et al., 2014, Metabolism), tracking closely with the decline in lean mass. BDNF levels in the hippocampus also decline with age, contributing to the cognitive deterioration that most people consider inevitable.

Sedentary Compounding

Inactivity accelerates the decline. A sedentary 60-year-old has both less muscle and less activation of the muscle they have – a double hit to myokine production. The chronic low-level inflammation of sedentary aging (inflammaging) is partly the result of losing the anti-inflammatory myokine signal that active muscle provides.

This creates a vicious cycle:

1. Inactivity reduces muscle mass
2. Less muscle reduces myokine secretion
3. Lower myokine output increases inflammation and metabolic dysfunction
4. Inflammation and metabolic dysfunction impair muscle protein synthesis
5. Muscle mass declines further

Breaking this cycle requires physical activity – specifically the type that maximally stimulates myokine release.

Key Takeaway: As you lose muscle with age (sarcopenia), you lose an endocrine organ — not just contractile tissue. The decline in myokine signaling contributes to increased inflammation, metabolic dysfunction, cognitive decline, and immune impairment. Maintaining muscle mass through resistance training is not just about strength; it is about preserving a critical hormonal communication system.

How to Maximize Myokine Production

Exercise Type Matters

Not all exercise produces the same myokine profile:

The key variable is muscle recruitment – both the volume of muscle engaged and the intensity of contraction. Compound resistance exercises (squats, deadlifts, rows) that recruit large muscle groups produce more myokines than isolation exercises (bicep curls, calf raises). High-intensity intervals produce larger acute spikes than steady-state cardio, though Zone 2 training produces a more sustained myokine release over a longer duration.

For a practical exercise protocol, see Exercise and Longevity: What Actually Moves the Needle and Strength Training for Longevity: Why Muscle Is a Survival Organ.

The Minimum Effective Dose

The myokine research supports the WHO physical activity guidelines as a minimum: 150 minutes of moderate-intensity aerobic activity per week plus two or more resistance training sessions. But the dose-response is clear – more muscle engagement and higher intensity produce more myokines, up to a point. An optimized longevity protocol (Zone 2 cardio + resistance training + occasional HIIT) covers all the myokine bases.

Can You Boost Myokines Without Exercise?

Not meaningfully. Cold exposure stimulates some myokines (particularly Metrnl and irisin), but the effect is smaller than exercise. No supplement replicates the full myokine cascade. This is why the concept of an "exercise pill" remains elusive – exercise does not activate one pathway. It activates hundreds of pathways simultaneously through a secretory organ that constitutes 40% of your body mass. No single molecule can replicate that breadth.

Some compounds support the myokine system indirectly:

• NMN and NAD+ precursors support mitochondrial function in muscle, potentially enhancing the energy substrate for myokine production during exercise. See What Is NMN?.
• Creatine supports the phosphocreatine energy system that powers high-intensity contractions – the contractions that produce the most myokines.
• Omega-3 fatty acids reduce the chronic inflammatory background against which myokines operate, potentially amplifying their anti-inflammatory signal.

But none of these replace the contraction signal itself. The muscle must contract – intensely, repeatedly, against meaningful resistance – for the myokine communication network to function.

Myokines and Specific Disease Prevention

The myokine network does not just promote general health – it provides mechanistic explanations for the specific disease-prevention effects of exercise that epidemiologists have documented for decades.

Type 2 Diabetes

Muscle-derived IL-6 and irisin both improve glucose uptake and insulin sensitivity independently of insulin signaling. Carey et al. (2006, Diabetes, n = 7 healthy men, human study) demonstrated that physiological concentrations of IL-6 (matching exercise-induced levels) directly increased glucose disposal in skeletal muscle through AMPK activation – bypassing the insulin receptor entirely. This means exercise improves blood sugar control through a myokine pathway that still functions even when insulin resistance has impaired the normal insulin signaling cascade.

Alzheimer's Disease and Neurodegeneration

The irisin-BDNF axis provides a direct molecular link between muscle contraction and brain protection. Lourenco et al. (2019, Nature Medicine, mouse study with human brain tissue validation) showed that irisin levels were reduced in the hippocampus and cerebrospinal fluid of Alzheimer's patients, and that boosting irisin (through exercise or direct administration) rescued memory in Alzheimer's mouse models. The study used human post-mortem brain tissue to confirm that irisin levels were depleted in Alzheimer's brains – translating the mouse findings to human relevance.

This provides a mechanistic explanation for the well-established epidemiological finding that regular exercise reduces Alzheimer's risk by 30-45% (Hamer & Chida, 2009, Psychological Medicine, meta-analysis of 16 prospective studies).

Depression

The myokine pathway also offers a biological explanation for exercise as an antidepressant. BDNF levels are consistently reduced in patients with major depressive disorder (Brunoni et al., 2008, Molecular Psychiatry, meta-analysis). Exercise increases BDNF through irisin signaling. Schuch et al. (2016, Journal of Psychiatric Research, meta-analysis of 25 RCTs) found that exercise had a large and significant antidepressant effect – comparable to pharmacotherapy in mild-to-moderate depression. The myokine framework explains why: exercise is not just a behavioral distraction from depression. It is pharmacology – a molecular intervention that increases the specific neurotrophic factors that depression depletes.

Osteoporosis

Myokines communicate directly with bone cells. Irisin stimulates osteoblast (bone-building cell) differentiation and activity while inhibiting osteoclastogenesis (the formation of bone-resorbing cells) (Colaianni et al., 2015, Proceedings of the National Academy of Sciences). This muscle-to-bone signaling pathway exists independently of the mechanical loading effect of exercise on bones, meaning muscle contraction provides a chemical signal to build bone in addition to the physical stimulus.

Key Takeaway: High-intensity exercise and resistance training produce the most robust myokine response. Irisin peaks during HIIT and resistance sessions. IL-6 release is proportional to muscle mass engaged and exercise duration. To maximize myokine production, prioritize compound movements (squats, deadlifts, presses) and include both resistance and high-intensity cardiovascular training weekly.

The mTOR-AMPK Connection

Myokine secretion is regulated by two master metabolic switches: mTOR (mechanistic target of rapamycin – a protein complex that promotes cell growth and protein synthesis) and AMPK (AMP-activated protein kinase – a protein that senses low cellular energy and activates pathways for energy production and cellular maintenance). Resistance training activates mTOR; endurance exercise activates AMPK. Both stimulate different myokine profiles.

This is why combining resistance training and aerobic exercise produces a broader myokine spectrum than either alone. The mTOR stimulus from lifting drives IL-15 and SPARC; the AMPK stimulus from cardio drives irisin and IL-6. The longevity-optimal protocol includes both – pulsing between anabolic (building) and catabolic (cleaning) states throughout the week. For the full picture on these master switches, see mTOR and AMPK: The Two Master Switches That Control How You Age.

Frequently Asked Questions

The Bottom Line: Your muscles are not just for movement -- they are the largest endocrine organ in your body, and every time you contract them intensely, they broadcast hundreds of health-promoting signaling molecules that no pill can replicate.

Related Reading

• Exercise and Longevity: What Actually Moves the Needle
• Strength Training for Longevity: Why Muscle Is a Survival Organ
• Inflammaging: The Silent Fire Accelerating How You Age
• mTOR and AMPK: The Two Master Switches That Control How You Age
• GLP-1 Drugs and Aging: What Ozempic Means for Longevity
• Grip Strength and Mortality: The Cheapest Longevity Test You Can Do