8 OCTOBER 2026 · LEE C. STONEHOUSE
Muscle as an Endocrine Organ: The Myokine Story Behind Strength Training Over 50
Skeletal muscle is not simply the tissue that moves the body.
It is also a signalling organ.
When muscle contracts, it releases messenger molecules called myokines. These signals communicate with muscle itself and with distant tissues, including fat, liver, brain, bone and the immune system.
This changes the meaning of strength training over 50.
The objective is not merely larger muscles or a better-looking physique. The objective is to create repeated, intelligent signals that help the body preserve capability, regulate energy, support repair and protect healthspan.
Lee C. Stonehouse became a personal trainer at 21 in California after competing as a bodybuilder. He later wrote The Healthspan Extension Manual and built the 10-Tenet operating system used by AGING?F***THAT! His own biological age was assessed at 47 against a chronological age of 63.
The principle is simple:
Measure the system. Apply the stimulus. Track the response. Repeat.
THE MUSCLE SIGNAL
Strength training is a biological message
The exercise tenet in Lee C. Stonehouse's framework is not an isolated gym habit. It is a deliberate way to send information through the body.
Mechanical tension, metabolic stress and repeated contraction alter the muscle's internal environment. In response, muscle fibres and nearby support cells release a collection of proteins and signalling molecules. Some act locally. Others enter circulation and influence tissues elsewhere.
This is known as muscle-organ crosstalk.
The research is still developing. Myokines do not all behave in the same way, and not every circulating molecule has been proven to originate mainly from skeletal muscle. However, the direction is clear: regular physical activity changes the conversation between muscle and the rest of the body.
A review in Endocrine Reviews describes skeletal muscle as a secretory organ capable of influencing metabolism, inflammation, tissue repair, the nervous system and other physiological functions through these signals (Muscle–Organ Crosstalk: The Emerging Roles of Myokines).
That makes muscle central to any serious discussion of healthspan, biological age and age reversal.
IL-6: THE EXERCISE PULSE
IL-6 is often described as an inflammatory molecule. That description is incomplete.
During exercise, contracting skeletal muscle can release IL-6 as a short-lived signal. The signal helps coordinate fuel availability and may influence glucose and fat metabolism. Research by Steensberg and colleagues demonstrated that contracting human muscle can produce IL-6 and contribute to the exercise-related increase in circulating IL-6.
The context matters.
A temporary exercise pulse is not the same as persistent elevation associated with chronic disease or prolonged inflammation. The same molecule can produce different effects depending on timing, concentration and the condition of the wider system.
Research by Carey and colleagues found that IL-6 can increase glucose disposal in humans and stimulate glucose uptake and fatty-acid oxidation through pathways involving AMP-activated protein kinase. A related study by Wolsk and colleagues examined IL-6 and fat metabolism in human skeletal muscle.
For someone over 50, the practical message is not to chase an IL-6 number. It is to create regular, tolerable muscle contractions through a balanced combination of resistance training, aerobic work and daily movement.
The muscle is being asked to communicate:
Energy is required. Fuel can be mobilised. The system is still active.
IRISIN: THE METABOLIC MESSENGER
Irisin is a fragment associated with the protein FNDC5. It became widely discussed because of research suggesting that exercise-related signalling may influence adipose tissue, energy expenditure and the conversion of some white fat cells toward a more metabolically active profile.
The concept is attractive, but the evidence needs disciplined interpretation.
Human studies have produced variable findings. Assay quality, training status, body composition, exercise intensity and the timing of blood sampling all affect the result. Irisin is not a validated standalone biological age test, and it should not be treated as proof of biological age reversal by itself.
Still, the signal is biologically interesting.
Irisin may be part of a wider communication network linking muscle with adipose tissue, metabolism and bone. A study of older adults published in Frontiers in Physiology examined circulating irisin and myostatin in relation to physical condition and muscle strength. Other research has explored how resistance training and nutrition influence these signals in older men (Circulating Irisin and Myostatin as Markers of Muscle Strength and Physical Condition in Elderly Subjects).
The sensible approach is to support the system that produces the signal:
- progressive resistance training;
- sufficient protein and overall nutrition;
- sleep that allows adaptation;
- recovery that matches training demand;
- consistency long enough for the body to remodel.
Myokines are not magic. They are part of the response to a well-designed stimulus.
MYOSTATIN: THE BRAKE ON MUSCLE ADAPTATION
Myostatin, also known as growth differentiation factor 8, helps regulate muscle growth. It acts partly as a biological brake, limiting excessive expansion of skeletal muscle tissue.
This matters in midlife because the body is constantly balancing signals that support maintenance, repair and growth against signals that limit them.
With inactivity, illness, undernutrition or prolonged stress, muscle can lose its ability to respond effectively. Aging-related muscle decline is not caused by myostatin alone, but myostatin-related signalling forms part of the wider biology of muscle atrophy and regeneration.
The opposing relationship between myostatin and follistatin is more useful than viewing either molecule in isolation. Exercise studies have reported changes in this balance alongside changes in strength and physical function. In older men, functional training has been associated with lower myostatin and higher follistatin, although results vary according to the exercise protocol and the population studied (Effects of functional training with blood occlusion on irisin, follistatin and myostatin).
The practical lesson is direct:
Muscle must receive a reason to remain.
That reason comes from progressive loading, adequate nutrition and repeated use. Sleep and recovery then provide the conditions in which adaptation can occur.
Without recovery, training becomes repeated disturbance. With recovery, it becomes information the body can use.
BDNF: MUSCLE, NERVES, REPAIR
BDNF is best known as a brain-derived neurotrophic factor. It supports processes associated with neurons, synaptic function and nervous-system adaptation.
Skeletal muscle also produces BDNF.
The role of muscle-derived BDNF is more complex than the popular claim that "exercise boosts brain BDNF". Research suggests that muscle BDNF can act locally within muscle, supporting neuromuscular-junction function, glucose handling, fat oxidation and muscle plasticity. Its direct endocrine route from muscle to brain is not yet firmly established in humans.
That distinction matters.
A 2022 review by Rentería and colleagues describes BDNF production in skeletal muscle and its role in neuromuscular function, muscle regeneration and metabolic processes (The Molecular Effects of BDNF Synthesis on Skeletal Muscle).
For healthspan, the important point is that strong movement depends on more than muscle fibre size. It depends on the relationship between muscle, nerves and the neuromuscular junction.
A person may have enough muscle tissue but still lack coordination, power or confidence. Well-designed training gives the nervous system a reason to keep communicating efficiently with that tissue.
This is one reason Lee's exercise tenet cannot be separated from the attitude tenet. The body needs a challenge, but the mind must remain willing to practise the challenge consistently.
DECORIN AND SPARC: THE REPAIR CREW
Decorin and SPARC belong to the extracellular matrix and tissue-remodelling side of the myokine story.
Decorin is involved in the organisation of connective tissue and the regulation of growth-factor activity. Research has suggested that decorin may interact with myostatin-related pathways and influence muscle growth and repair.
SPARC is a matricellular protein involved in communication between cells and the extracellular matrix. Resistance exercise can alter SPARC expression in muscle, while experimental research points toward roles in tissue remodelling, repair and protection against atrophy.
These are not simple blood-test targets for the public. Their importance lies in the larger picture: muscle is not an inert bundle of fibres. It is a living tissue embedded in a structural environment that must continually adapt.
That environment includes:
- collagen and connective tissue;
- blood supply;
- satellite cells;
- immune cells;
- nerves;
- bone and tendon interfaces.
Training therefore creates more than a muscle-building signal. It creates a repair and maintenance demand.
That demand must be matched by nutrition, sleep, stress control and recovery. If those supporting tenets are neglected, the signal may be present but the construction materials and repair conditions may be inadequate.
MUSCLE, IMMUNITY AND BONE
Muscle contraction also interacts with immune surveillance and bone biology.
Exercise-related signals can influence immune-cell behaviour and the inflammatory environment surrounding tissue repair. IL-6, for example, has different effects when released transiently during exercise compared with persistently elevated inflammatory signalling. The research reviewed by Muñoz-Cánoves, Scheele and Pedersen shows how IL-6 can participate in energy regulation, muscle regeneration and immune-related processes while also producing harmful effects in chronic disease contexts (IL-6 myokine signalling in skeletal muscle).
Bone is also responsive to mechanical loading and biochemical communication. Muscle and bone share signalling pathways that help coordinate movement, structure and repair. Stronger muscle changes the mechanical environment experienced by bone, while exercise-related molecules may contribute to muscle-bone communication.
This is why a DEXA scan, sometimes searched as a dexascan, can be useful within a wider assessment system. Body composition and bone measurements do not tell the whole story, but they add information that a mirror cannot provide.
The same principle applies to VO2max, strength testing and blood markers of longevity. Each measure gives one view of the operating system. The value comes from combining them rather than treating any single result as the whole truth.
BIOLOGICAL AGE IS A NETWORK
The myokine story helps explain why biological aging cannot be reduced to one molecule.
Myokines may influence metabolic flexibility, immune regulation, tissue repair, nervous-system function and muscle preservation. Those systems then influence one another.
Poor sleep can reduce training quality. High stress can impair recovery. Inadequate nutrition can limit adaptation. Loss of muscle can reduce daily movement. Reduced movement can worsen metabolic health and body composition.
The reverse is also possible.
Better training can improve physical capacity. Better capacity can support more movement. More movement can improve metabolic regulation and confidence. Nutrition and sleep can then reinforce the adaptation.
This is the logic behind Lee C. Stonehouse's 10-Tenet operating system. Exercise is the stimulus, but the result depends on the full system:
- Attitude, reject passive acceptance of decline.
- Nutrition, provide the materials for repair and performance.
- Exercise, create a progressive signal.
- Sleep, protect adaptation.
- Stress control, reduce unnecessary biological noise.
- Hormones and genetics, understand individual context.
- Self-care, maintain the physical platform.
- Love and community, reinforce behaviour and meaning.
- Consistency, repeat long enough to create change.
- Cosmetic presentation, reflect capability on the outside.
The AFT biological age calculator and model tracks modifiable physiological measures across biomarkers, body composition, fitness, blood and vital signs. It is a programme-tracking model, not a diagnosis, prognosis or prediction of lifespan.
That distinction is important. No single myokine currently proves biological age reversal. The strongest practical case is for repeated exercise within a broader healthspan method, followed by objective measurement.
WHAT STRENGTH TRAINING OVER 50 SHOULD ACHIEVE
Strength training over 50 should not be designed around punishment.
It should be designed around progressive capability.
The programme should develop strength, power, control, mobility and work capacity while respecting the individual's current condition. Aerobic training matters too. VO2max provides valuable information about cardiorespiratory fitness and should sit alongside resistance training rather than being ignored.
The starting point may be simple:
- assess current strength and movement capacity;
- establish a repeatable resistance-training routine;
- add aerobic work appropriate to current fitness;
- record response, recovery and performance;
- progress gradually.
A biological age test can then be interpreted alongside changes in strength, body composition, VO2max, sleep, blood markers and daily function. This is how the question "how to reverse biological age" becomes practical rather than abstract.
Lee C. Stonehouse's Elite Age Reversal Program and longevity clinic in Brighton applies this approach through progressive phases, measured assessments and intervention across the 10-Tenet framework.
The goal is not to worship muscle.
The goal is to preserve the ability to use it.
LEE C. STONEHOUSE'S PRACTICAL POSITION
Lee C. Stonehouse built his method around a conclusion developed through personal experience and professional practice: physical decline should be measured rather than guessed at.
His own biological age was assessed at 47 against a chronological age of 63. That result does not make a promise for every individual. It demonstrates the type of change the AFT system is designed to track: a measurable divergence between chronological age and selected physiological markers.
The myokine story adds depth to that method.
Every well-managed training session may create a short-lived biochemical conversation. Repeated over months and years, those conversations may help preserve muscle, metabolic flexibility, repair capacity and physical independence.
That is healthspan vs lifespan and age reversal articles in practical form.
Not merely living longer.
Remaining capable for longer.
FREQUENTLY ASKED QUESTIONS
What are myokines and why do they matter after 50?
Myokines are signalling molecules released by skeletal muscle, particularly during contraction. They can act within muscle or communicate with other tissues. After 50, preserving regular muscle activity may support metabolic health, physical function, repair and nervous-system communication.
Can strength training increase irisin and reduce myostatin?
Research suggests that exercise can alter irisin, myostatin and follistatin signalling, but responses vary between individuals and studies. Training mode, intensity, age, nutrition and sampling time all matter. Train for measurable performance rather than one blood value.
Does muscle-derived BDNF improve brain function?
Skeletal muscle produces BDNF, and exercise is associated with changes in BDNF-related signalling. Muscle-derived BDNF has clearer evidence for local roles in neuromuscular function, muscle metabolism and repair than for a direct muscle-to-brain endocrine pathway in humans.
Is IL-6 from exercise harmful?
Exercise-related IL-6 is usually a temporary signal linked to contracting muscle and fuel regulation. That is different from persistent elevation in chronic inflammation or disease. IL-6 is context-dependent and should not be labelled simply good or bad.
How can someone measure biological age reversal?
A credible approach combines a repeatable biological age test with objective measures such as blood biomarkers, body composition, fitness, strength, vital signs and lifestyle tracking. Results are most useful when they guide interventions and are reassessed over time.
THE NEXT STEP
The myokine story is a reminder that every contraction is information.
The question is whether that information is being created consistently, supported properly and measured objectively.
To enquire about the Elite Age Reversal Program, contact Lee C. Stonehouse exclusively on WhatsApp by text, voice note or voice call. The program serves clients within a 10 mile radius of Brighton & Hove city centre.
DEEP DIVE: NAMED SOURCES
- Muscle–Organ Crosstalk: The Emerging Roles of Myokines, Endocrine Reviews.
- Steensberg et al., on IL-6 production from contracting human muscle.
- Carey et al., on IL-6 and glucose disposal through AMPK-related pathways.
- Wolsk et al., on IL-6 and fat metabolism in human skeletal muscle.
- Circulating Irisin and Myostatin as Markers of Muscle Strength and Physical Condition in Elderly Subjects, Frontiers in Physiology.
- Effects of functional training with blood occlusion on irisin, follistatin and myostatin.
- Rentería et al., The Molecular Effects of BDNF Synthesis on Skeletal Muscle, 2022.
- Muñoz-Cánoves, Scheele and Pedersen, IL-6 myokine signalling in skeletal muscle.
- The AFT healthspan and age-reversal programme.
- More healthspan articles.
Ready to measure the system and start changing it?