Muscle as an Endocrine Organ: How Your Muscles Communicate with Your Brain, Bones, Immune System and Metabolism

Muscle as an Endocrine Organ

How skeletal muscle communicates with your brain, bones, immune system and metabolism—and why regular movement matters far beyond strength.

Muscle is easy to notice when it produces movement: lifting a suitcase, climbing stairs or catching your balance. Less visible is the work skeletal muscle does as a metabolic and signalling tissue. It uses and stores fuel, produces heat and releases molecules that can act within muscle, on nearby cells or elsewhere in the body.

This is why researchers increasingly describe skeletal muscle as an endocrine organ. The description does not mean muscle replaces the thyroid, pancreas or other endocrine glands. It means muscle participates in chemical communication as well as movement—and that communication is one part of the wider response to physical activity.

Key Takeaways

1. Skeletal muscle is a contractile, metabolic and signalling tissue—not simply machinery attached to bone.

2. Muscle produces myokines and other signals that can act locally or participate in communication with distant tissues.

3. Exercise affects the whole body through several routes at once, including nerves, blood flow, fuel use, mechanical loading and chemical signalling.

4. The source, timing and context of a signal matter; not every proposed myokine has a proven whole-body effect in humans.

5. Regular movement, aerobic activity and resistance training create complementary benefits that cannot be reduced to one molecule.

6. Nutrition and recovery support working muscle, but no food or supplement reproduces the complete biological response to exercise.

What Does ‘Endocrine Organ’ Mean?

An endocrine organ releases chemical messengers that influence other cells and tissues. Classical examples include the thyroid and pancreas. Skeletal muscle also produces a large and changing collection of signalling molecules, often called its secretome.

Many muscle-derived proteins and peptides are known as myokines. Their reach varies:

1. Autocrine signals act on the cell that released them.

2. Paracrine signals act on nearby cells and tissues.

3. Endocrine signals enter the circulation and act at more distant sites.

This distinction is important. A molecule made by muscle is not automatically a circulating hormone, and detecting a molecule after exercise does not prove that muscle was its only source. The wider term ‘exerkine’ includes exercise-responsive signals released by muscle and other tissues.

Muscle Has More Than One Job

Calling muscle an endocrine organ adds to its traditional roles rather than replacing them. Skeletal muscle helps the body:

1. Generate force for movement, posture and breathing.

2. Use glucose and fatty acids to meet changing energy demands.

3. Store glycogen for later activity.

4. Produce heat, including through shivering and energy use.

5. Absorb mechanical load and work with tendons, joints and bones.

6. Release signals involved in local adaptation and inter-organ communication.

These roles overlap. Walking after a meal, for example, uses muscle contractions, increases fuel demand, changes blood flow and activates intracellular pathways. The result is not one isolated ‘message’ but a coordinated physiological response.

How Muscles Communicate

Muscle communication is not a one-way broadcast. The brain, hormones, nutrients, immune cells and neighbouring tissues all influence muscle. Muscle then sends information back through several channels.

Nervous-System Feedback

Sensory receptors in muscles and tendons report length, tension and movement. This rapid neural feedback helps the brain coordinate posture, balance and force. It is different from endocrine signalling, but it is central to the two-way muscle–brain conversation.

Mechanical Signals

When muscle pulls on bone and tendon, cells detect force and convert it into biological responses. This process, called mechanotransduction, helps explain why loading matters for musculoskeletal adaptation.

Metabolic Signals

Changes in energy use, oxygen demand, temperature, blood flow and metabolites tell cells that work is occurring. These signals can alter fuel use and gene expression within muscle.

Myokines and Other Secreted Factors

Muscle can release proteins, peptides, metabolites and extracellular vesicles. Some act locally; some enter circulation. Their pattern depends on the activity, intensity, duration, muscles recruited, training status, nutrition and when researchers measure them.

Myokines: A Growing but Evolving Field

Interleukin-6 is among the best-studied exercise-related myokines. Contracting muscle can release it during exercise, where it participates in fuel mobilisation and immune signalling. IL-6 is also produced by other tissues during infection and disease, so source, concentration, timing and surrounding signals all change how it should be interpreted.

Other candidates include myostatin, IL-15, irisin, apelin, musclin and many more. Some have substantial mechanistic evidence; others remain uncertain in humans. Measurement can be difficult, and results from cells or animals do not automatically establish a practical benefit for people.

The useful conclusion is not that one ‘good’ myokine explains exercise. It is that active muscle participates in a network of context-dependent signals. For the immune side of this story, read Inflammation Explained.

The Muscle–Brain Conversation

The brain initiates voluntary movement, while muscle and sensory nerves continuously report what happened. Practice improves how the nervous system recruits motor units, coordinates joints and corrects errors. This neural learning is one reason people can become stronger or more skilful before muscle size changes markedly.

Researchers are also studying whether muscle-derived exerkines contribute to exercise-related changes in mood, cognition and brain plasticity. That work is promising but complex: many circulating factors have several tissue sources, and exercise also changes cerebral blood flow, sleep, metabolic health and learning opportunities.

It is therefore too simple to say that one myokine travels from muscle and ‘switches on’ the brain. Explore the established neural mechanisms in Why Strength Isn’t Just About Muscle.

The Muscle–Bone Partnership

Muscle and bone communicate first through force. When muscles pull on the skeleton during appropriately loaded movement, bone cells receive mechanical information that can contribute to remodelling. Balance and strength also help people manage everyday loads and reduce some fall risks.

Chemical communication adds another layer. Muscle-derived myokines and bone-derived osteokines are being studied as messengers between the tissues. Many proposed pathways are still based on experimental models, so it would be misleading to promise that increasing one myokine will strengthen bone.

For daily life, the partnership is easy to see: the same sit-to-stand movement challenges leg muscle, loads bone, rehearses balance and trains the nervous system at once.

Muscle, Glucose and the Liver

Skeletal muscle is a major site of glucose disposal, particularly after eating and during activity. Insulin helps move glucose into muscle cells, while contraction can stimulate glucose uptake through partly independent pathways. Muscle can store glucose as glycogen and use it during later activity.

The liver helps maintain circulating glucose between meals and during exercise. As demand changes, hormones, nerves, blood flow, metabolites and muscle-derived signals all contribute to coordination. It is inaccurate to credit one myokine with the entire response.

Training also changes muscle itself—its enzymes, capillaries, mitochondria and responsiveness to insulin. Read The Muscle–Mitochondria Connection.

Muscle and Fat Tissue

Fat tissue is also an active endocrine organ. It releases adipokines and stores or releases fatty acids according to the body’s needs. Muscle and fat communicate through hormones, metabolites and inflammatory signals as well as the energy demands created by movement.

This relationship is not a battle in which one tissue must ‘defeat’ the other. Both are normal tissues with essential roles. Health depends on their function, distribution and interaction within the whole person—not on a simplistic muscle-versus-fat story.

Muscle and the Immune System

Exercise temporarily alters immune-cell traffic and inflammatory signals. Muscle-derived factors can participate in fuel availability, tissue repair and immune coordination. These short-lived exercise responses are not the same as persistent systemic inflammation associated with some diseases.

A workout does not instantly ‘boost’ immunity, and harder is not always better. Illness, sleep loss, inadequate food and excessive training can change the response. Sustainable activity and appropriate recovery matter more than chasing a dramatic signal.

The Emerging Muscle–Gut Axis

The gut influences muscle by digesting and absorbing nutrients and through microbial metabolites, immune pathways and hormones. In the other direction, physical activity changes circulation, energy use, intestinal transit and signalling throughout the body.

Researchers are investigating whether myokines are part of this bidirectional relationship, but the human evidence is still developing. The gut microbiome varies greatly between people, and associations do not prove that a particular microbe or myokine caused an outcome. Continue with The Gut–Muscle Axis.

What Changes With Inactivity and Ageing?

Muscle adapts to demand. When activity falls, strength, power, aerobic capacity and movement confidence can decline. Ageing may also bring changes in motor units, hormones, appetite, recovery, illness burden and anabolic responsiveness. None of this means muscle stops adapting.

Regular resistance training can improve strength and function in later life, while aerobic, balance and mobility activities support complementary capacities. The most suitable starting point depends on health, experience and current function. Read Why Movement Gets Harder With Age.

Movement Is a Whole-Body Input

Describing movement as ‘information’ can be helpful if the metaphor is kept accurate. A brisk walk, gardening session or set of squats changes mechanical load, energy demand, circulation, nervous-system activity and chemical signalling together. Not every step releases the same myokines, but every bout of movement contributes to the body’s total activity pattern.

Current Australian guidance for adults recommends several hours of light activity daily, moderate-to-vigorous activity on most days, muscle-strengthening activity on at least two days each week, and regular mobility, balance and coordination work. Long periods of sedentary behaviour should be broken up as often as possible.

A Practical Muscle-Supporting Week

1. Move lightly across the day and interrupt long periods of sitting.

2. Use walking, cycling, swimming or another suitable activity to build aerobic capacity.

3. Challenge major muscle groups with resistance work on at least two days each week.

4. Practise balance, mobility and coordination regularly.

5. Increase difficulty gradually rather than changing volume, intensity and frequency at once.

6. Allow sleep, nutrition and easier days to support adaptation.

People returning after a long break, living with a health condition or experiencing pain may benefit from advice from a GP, physiotherapist or accredited exercise physiologist.

Nutrition Supports the Tissue Doing the Work

Movement supplies the challenge; food supplies energy and nutrients. Protein provides amino acids for continual tissue turnover, while carbohydrate can fuel activity and replenish glycogen. Dietary fats, vitamins, minerals and fluid also support normal physiology.

No single meal controls muscle’s endocrine function. A varied eating pattern built around suitable protein foods, vegetables, fruit, whole grains, legumes, nuts, seeds and other whole foods is more useful than searching for a ‘myokine food’. Learn more in Protein Turnover Explained, Why Protein and Resistance Training Work Better Together and The Food Matrix Explained.

Where Bone Broth Fits

Bone broth can contribute fluid, flavour and collagen-derived protein to a varied diet. Protein and sodium vary by product, and collagen is not a complete protein. Bone broth does not release myokines or reproduce exercise; contraction is the relevant stimulus for exercise-related muscle signalling.

Use it as a warm drink or an ingredient in soups, stews, sauces and grain dishes, alongside a range of other protein and whole-food choices.

· Bone Broth Benefits: The Complete Guide

· Shop Broth & Co bone broth collection

Recovery Is Part of the Signal

A training session starts a response; adaptation unfolds afterwards. Sleep, adequate energy and nutrients, hydration and sensible spacing help the body restore fuel and remodel tissues. More training is not automatically more productive when recovery capacity is repeatedly exceeded.

Learn how to match challenge and recovery in Why Recovery Matters More Than Ever After 40.

Common Myths

Myth: Every contraction releases powerful hormones to every organ

Fact: Signal patterns vary, many effects are local and some proposed distant actions remain uncertain in humans.

Myth: One myokine explains all the benefits of exercise

Fact: Exercise affects neural, vascular, mechanical, immune and metabolic systems simultaneously.

Myth: More intense exercise always creates better communication

Fact: The useful dose depends on the individual, the goal and the capacity to recover. Consistency matters.

Myth: Muscle health is mainly about appearance

Fact: Strength, balance, mobility, fuel use and the ability to perform daily tasks are more meaningful measures of function.

Myth: A supplement can copy exercise signalling

Fact: No supplement reproduces the combined mechanical, neural, circulatory and metabolic effects of physical activity.

Frequently Asked Questions

Is skeletal muscle really an endocrine organ?

Yes. Skeletal muscle produces and releases signalling molecules, some of which act at distant sites. It is also a contractile and metabolic organ, and much of its signalling is local.

What are myokines?

Myokines are muscle-produced proteins or peptides that act on the same cell, nearby tissues or, in some cases, distant organs through the circulation.

Does walking activate endocrine muscle?

Walking uses skeletal muscle and changes metabolic and signalling activity. The exact response depends on pace, duration, fitness, muscles recruited and the molecule measured.

Is resistance training more important than aerobic exercise?

They provide overlapping and distinct benefits. Resistance work is especially useful for strength and muscle function; aerobic activity develops cardiovascular and metabolic capacity. A balanced programme generally includes both.

Can older muscle still adapt?

Yes. The rate and size of adaptation vary, but appropriately progressed resistance and aerobic exercise can improve function in later life.

Can food increase myokines?

Food supports the tissue and the exercise response, but myokines are not nutrients. No food replaces muscle contraction or the wider effects of movement.

Does soreness mean my muscles sent more signals?

No. Soreness often reflects novelty and tissue stress and is not a reliable measure of myokine release or training quality.

Final Thoughts

Skeletal muscle is not a passive recipient of instructions. It senses load and fuel demand, communicates through nerves and chemical signals, and works with the brain, liver, fat tissue, bone, gut and immune system.

The science is most useful when it broadens our view of movement without exaggerating it. Exercise benefits come from networks, not one miracle molecule. Regular, appropriate activity—supported by food, sleep and recovery—helps keep those networks working across a lifetime.