Exercise is often described as a way to burn calories, strengthen muscles and improve heart health. But there is another fascinating side to exercise: when we move our bodies, our muscles, brain, adrenal glands and other organs communicate with each other by releasing hormones and hormone-like substances.

In fact, skeletal muscle is now considered an endocrine organ because contracting muscles release biologically active substances called myokines, which can influence metabolism, inflammation, the brain, immune system and other organs.

The hormonal response to exercise is not the same every time. There is a difference between what happens during one exercise session and what happens after months or years of regular exercise.

1. What happens during the first few minutes of exercise?

When you start walking, running, cycling or exercising, your body immediately recognizes that its energy requirements have increased.

The sympathetic nervous system becomes activated and the adrenal glands release adrenaline and noradrenaline.

Adrenaline and noradrenaline

These hormones help the body respond to the increased physical demand.

They:

Increase heart rate
Increase blood flow to working muscles
Help mobilize glucose for energy
Promote breakdown of stored fat
Improve alertness and readiness
Help maintain blood pressure during exercise

Studies show that vigorous exercise can produce substantial temporary increases in catecholamines such as adrenaline and noradrenaline. These levels generally return toward baseline after exercise.

This is one reason you may feel energized and mentally alert after exercise.

2. Cortisol — the misunderstood stress hormone

Cortisol is frequently called the "stress hormone," but cortisol is not necessarily harmful.

During exercise, particularly prolonged or intense exercise, cortisol can increase.

Its job is to help the body provide enough fuel for the exercise session.

It helps:

Maintain blood glucose
Mobilize energy stores
Support blood pressure
Coordinate the body's response to physical stress

However, exercise intensity, duration, fitness level and individual characteristics all influence the cortisol response.

Regular exercise can also change the way the stress-response system reacts to exercise. Some forms of regular training, particularly high-intensity interval training, have been associated with lower resting cortisol in some studies.

The important message

A temporary rise in cortisol during exercise is a normal physiological response.

The goal is not to eliminate cortisol. The goal is to develop a healthy and adaptable stress-response system.

3. Growth hormone — released during exercise

Exercise, particularly higher-intensity aerobic and resistance exercise, can stimulate the release of growth hormone (GH).

GH is involved in:

Tissue repair
Protein metabolism
Fat metabolism
Muscle and bone physiology
Recovery and adaptation

Both aerobic and resistance exercise can produce an acute increase in growth hormone.

Importantly, however, a temporary exercise-related increase in GH should not be interpreted as meaning that more GH is always better. Hormones work as part of a complex physiological system.

4. Endorphins — the famous "feel-good" chemicals

Exercise can influence the brain's opioid system and increase endorphin activity.

Endorphins are associated with:

Reduced perception of pain
Improved mood
Feelings of well-being
Better tolerance of physical effort

This may contribute to the feeling many people describe as:

"I feel better after exercising."

But the exercise-related improvement in mood is not caused by endorphins alone. The brain responds to exercise through multiple pathways, including neurotransmitters and other signaling molecules.

5. Dopamine and serotonin — exercise and the brain

Exercise also influences neurotransmitter systems involved in mood, motivation, reward and emotional well-being.

Dopamine

Dopamine is important for:

Motivation
Reward
Attention
Learning
Movement

Serotonin

Serotonin participates in:

Mood regulation
Sleep
Appetite
Emotional regulation

This is one reason regular physical activity can be useful as part of a healthy strategy for improving mood and psychological well-being.

6. BDNF — fertilizer for the brain

One particularly interesting molecule influenced by exercise is brain-derived neurotrophic factor (BDNF).

BDNF supports:

Neuronal survival
Learning
Memory
Brain plasticity

BDNF is sometimes described as a kind of "fertilizer for the brain."

Exercise-induced BDNF responses have been studied extensively, although the exact response varies depending on the exercise type, intensity, timing and individual characteristics.

This provides one biological explanation for why regular exercise is associated with better cognitive and psychological health.

7. The muscle itself becomes an endocrine organ

This is perhaps the most exciting development in exercise biology.

When muscles contract, they release signaling molecules known as myokines.

Some important examples include:

IL-6
IL-15
Irisin
BDNF
Myostatin
FGF21
SPARC
Apelin

These substances communicate between muscle and other organs, including the liver, fat tissue, brain, bones and immune system.

8. IL-6 — inflammation is not always bad

IL-6 is an interesting example because it can have different biological effects depending on its context.

During exercise, contracting skeletal muscle can release IL-6.

Exercise-associated IL-6 signaling participates in:

Energy metabolism
Mobilization of energy substrates
Communication between muscle and other tissues
Regulation of inflammatory responses

This is different from the chronic inflammatory state associated with persistent disease.

Therefore, it is important to distinguish short-lived exercise-related signaling from chronic inflammation.

9. Irisin — the exercise-associated myokine

Irisin is another molecule released in association with muscle activity.

It has attracted considerable scientific interest because experimental studies suggest roles in:

Energy metabolism
Adipose tissue biology
Glucose metabolism
Muscle adaptation

However, the science surrounding irisin is still developing, and the magnitude and physiological importance of changes in humans remain an active research area.

10. Insulin — exercise makes the body use glucose better

Exercise has a powerful effect on insulin sensitivity.

During and after exercise, skeletal muscle becomes more efficient at taking up glucose.

With regular exercise, many people develop improved:

Insulin sensitivity
Blood glucose regulation
Metabolic health
Body composition

This is particularly important because insulin resistance is associated with obesity, type 2 diabetes and several chronic diseases.

Studies in cancer survivors have also demonstrated improvements in insulin and insulin resistance following exercise interventions.

11. What changes after months and years of exercise?

This is where exercise becomes particularly powerful.

One workout produces a temporary hormonal response.

Years of regular exercise produce adaptation.

The body becomes better at regulating:

Blood glucose
Blood pressure
Energy metabolism
Inflammation
Cardiovascular function
Muscle mass
Fat mass
Stress responses
Physical fitness

Exercise training has also been associated in studies with changes in several anabolic hormones, including testosterone, IGF-1, growth hormone and DHEA, although responses vary considerably according to age, sex, exercise type, intensity and individual factors.

The goal should therefore not be:

"How can I maximize my hormones?"

Instead, the goal should be:

"How can I make my body more metabolically, physically and psychologically resilient?"

12. Can exercise help prevent cancer recurrence?

This is an extremely important question for cancer survivors.

The answer needs some nuance.

Yes — there is encouraging evidence.

But exercise should not be described as a proven replacement for cancer treatment, and we should not claim that exercise guarantees that cancer will not return.

Research has consistently found associations between physical activity after cancer diagnosis and better outcomes, particularly in breast, colorectal and prostate cancer survivors.

For example, the National Cancer Institute reports that among breast cancer survivors, higher physical activity has been associated with substantially lower overall and breast-cancer mortality. Similar associations have been observed in colorectal and prostate cancer survivors.

13. What about breast cancer recurrence specifically?

This is an area of considerable research.

A meta-analysis involving almost 30,000 breast cancer survivors found that post-diagnosis recreational physical activity was associated with approximately a 16% lower risk of breast cancer recurrence and a 23% lower risk of recurrence or disease-specific mortality.

Another meta-analysis of prospective studies found that women achieving at least approximately 7.5 MET-hours/week of recreational physical activity had a lower risk of breast cancer recurrence than women with very low activity levels.

However, not every study has found a statistically significant reduction in recurrence. A Global Cancer Update Programme review found strong evidence for improved survival but did not find a clear association with recurrence in its pooled analysis.

Therefore, the most scientifically responsible statement is:

Regular physical activity is associated with better survival among many cancer survivors and may reduce recurrence risk, particularly in breast cancer, but the evidence for recurrence prevention is not equally strong for every cancer type and is not proof of causation.

14. What about colorectal cancer?

The evidence is also encouraging.

A 2024 systematic review and meta-analysis involving more than 82,000 colorectal cancer patients found that physical activity after diagnosis was consistently associated with lower risks of adverse outcomes, although the authors emphasized important limitations of observational studies.

For cancer recurrence specifically, the expert panel classified the evidence as limited-suggestive, meaning the findings are promising but stronger research is still needed.

15. How could exercise potentially influence cancer biology?

Scientists are studying several possible mechanisms.

Exercise may influence:

1. Insulin and metabolic pathways

Improved insulin sensitivity may reduce unfavorable metabolic signaling.

2. Body fat

Maintaining a healthy body composition can reduce metabolic and inflammatory abnormalities.

3. Chronic inflammation

Regular exercise can influence inflammatory signaling and immune regulation.

4. Immune function

Exercise interacts with immune cells and immune surveillance.

5. Myokines

Exercise-induced muscle signals may communicate with other tissues and potentially influence tumor biology.

6. Hormonal environment

Physical activity can influence insulin, sex hormones, cortisol and other endocrine pathways.

7. Cardiovascular fitness

Better cardiovascular health reduces competing causes of illness and death.

The possibility that myokines influence cancer-related inflammation and the tumor microenvironment is an active area of research, but many of these mechanisms remain experimental rather than proven clinical explanations.

16. Exercise is not only about preventing recurrence

For a cancer survivor, exercise can be valuable even when we cannot prove that it prevents recurrence.

Evidence supports exercise for improving:

Cancer-related fatigue
Physical functioning
Anxiety
Depressive symptoms
Quality of life
Cardiovascular fitness
Muscle strength
General metabolic health

An international multidisciplinary consensus concluded that exercise is generally safe for cancer survivors and that survivors should avoid inactivity, with exercise programs adapted to the person's cancer, treatment history, physical condition and treatment-related effects.

17. How much exercise should a cancer survivor do?

There is no single prescription that is suitable for everyone.

A cancer survivor's exercise program should consider:

Cancer type and stage
Surgery
Chemotherapy
Radiation therapy
Hormonal therapy
Immunotherapy
Bone health
Anemia
Neuropathy
Heart and lung function
Age
Previous fitness level

For many survivors, a gradual combination of aerobic exercise and resistance training is an excellent long-term goal.

The most important principle is:

Start where you are. Progress gradually. Stay consistent.

Someone who cannot run does not need to run.

Walking is exercise.

Cycling is exercise.

Swimming is exercise.

Strength training is exercise.

Even short periods of movement are better than remaining completely inactive.

The Bigger Picture

Exercise does something extraordinary.

The medicine is not coming from a tablet.

Your muscles themselves participate in producing a complex biological response involving hormones, myokines, neurotransmitters, immune signals and metabolic pathways.

A single workout can temporarily change adrenaline, noradrenaline, cortisol, growth hormone and other signaling systems.

But repeated exercise produces something much more important:

Adaptation.

The heart becomes fitter.

The muscles become stronger.

Insulin sensitivity improves.

Metabolism becomes healthier.

The brain receives beneficial signals.

Mood and sleep may improve.

Body fat can decrease.

Physical function improves.

And for many cancer survivors, regular physical activity is associated with better quality of life and longer survival, with encouraging evidence that it may also reduce recurrence risk for some cancers.

But exercise should be viewed as one important component of survivorship care — not a substitute for appropriate cancer treatment, surveillance, medication or medical advice.

A message to every cancer survivor

After completing cancer treatment, it is natural to worry:

"Will my cancer come back?"

That fear can sometimes become a constant part of life.

Instead of living only in fear of recurrence, gradually begin asking:

"What can I do today to make my body stronger?"

Take a walk.

Do some stretching.

Build your muscle strength.

Spend time outdoors.

Improve your sleep.

Eat a balanced diet.

Return to the activities you love.

And slowly rediscover the person you were before cancer — perhaps an even stronger version of yourself.

Exercise cannot promise that cancer will never return.

But it can help you build a stronger heart, stronger muscles, better metabolic health, greater confidence and a better quality of life.

And that is a powerful reason to keep moving.

— Dr. M. G. Giriyappagoudar
Senior Consultant Radiation Oncologist
HCG Cancer Centre, Hubballi

Exercise: The Hormonal Medicine Your Body Makes for Itself How exercise changes your hormones — from the first few minutes to many years of regular activity