What Hormones Are Released During Exercise?

Exercise triggers the release of dozens of hormones and hormone-like molecules, spanning nearly every major gland and organ system in the body. The mix shifts depending on how hard you work, how long you keep going, what type of exercise you do, and even what time of day you do it. Some of these hormones, like adrenaline and cortisol, spike within seconds to minutes. Others, like growth hormone and certain muscle-derived signaling molecules, build over the course of a session. Understanding which hormones respond and why gives a much richer picture of exercise than “it burns calories.”

Adrenaline and Noradrenaline

The moment you start moving with any real effort, your sympathetic nervous system fires up and your adrenal glands dump adrenaline (epinephrine) and noradrenaline (norepinephrine) into your bloodstream. Both hormones rise in proportion to how hard and how long you exercise.¹ Their job is to prepare your body for sustained effort: your heart rate climbs, airways widen, and blood gets shunted toward working muscles.

These catecholamines also have a major behind-the-scenes role in fueling the workout itself. They suppress insulin secretion and act directly on fat and glycogen stores, helping to unlock both sugar and fat for energy.¹ That dual action, slowing insulin while accelerating fuel mobilization, is one reason your body can sustain surprisingly intense effort without running out of gas immediately. You feel this as the rush at the start of a hard run or the alertness that kicks in during a heavy set of squats.

Cortisol and the Intensity Threshold

Cortisol often gets a bad reputation as “the stress hormone,” but during exercise it serves a practical purpose: it helps maintain blood sugar, supports fat metabolism, and manages inflammation. What makes cortisol interesting is that it doesn’t simply go up whenever you move. There appears to be an intensity threshold below which cortisol barely budges, or even drops.

Research comparing different exercise intensities found that working at about 40% of maximum capacity produced no meaningful rise in cortisol, and once adjustments were made for plasma volume changes and circadian rhythm, that low-intensity work actually lowered circulating cortisol. At 60% intensity, cortisol rose by roughly 40%, and at 80% it jumped by about 83%.² This is a useful detail for people who worry about cortisol: an easy walk or gentle yoga session is unlikely to spike it. Moderate-to-hard efforts are a different story, and that spike is a normal, healthy part of how the body responds to physical challenge.

High-intensity interval training and heavy resistance work reliably trigger cortisol alongside growth hormone, and the two often rise together during demanding sessions.³ The acid buildup that comes with intense work (that burning sensation in your muscles) appears to be part of the signal that pushes both hormones upward.

Insulin and Glucagon

While catecholamines are flooding in, the pancreas is quietly adjusting its own output to keep blood sugar in a safe range. At the onset of exercise, blood glucose actually ticks upward briefly. After about 30 minutes of sustained, submaximal effort, glucose starts to fall, which triggers a drop in insulin and a rise in glucagon.⁴ That shift tells the liver to release more glucose, keeping the brain and muscles fed.

This insulin-glucagon dance is especially relevant if you have diabetes or take medications that affect blood sugar. The natural decline in insulin during exercise is a feature, not a bug, but it can interact unpredictably with injected insulin or certain oral medications. Anyone managing blood sugar with medication should be aware that exercise changes the hormonal backdrop the drug is working against.

Growth Hormone

Growth hormone (GH) is one of the most exercise-responsive hormones in the body, and intensity matters enormously. High-intensity work, whether it’s sprints, heavy lifting, or interval training, produces the largest GH spikes.³ Low-intensity exercise produces far less of a bump. The acid environment created by intense effort seems to be a key trigger, which is why protocols with short rest periods and high metabolic stress tend to drive GH higher than, say, a long easy jog.

Resistance training can induce GH release in both young and older adults, though the magnitude of the response tends to be smaller in older populations.⁵ GH supports tissue repair, fat metabolism, and muscle protein synthesis, which is part of why recovery from a hard workout involves not just rest but a hormonal environment geared toward rebuilding.

Testosterone

Exercise can raise circulating testosterone, but the effect depends on the type of exercise, your age, your sex, and a long list of individual factors.⁶ Heavy resistance training is the most reliable stimulus. Younger men tend to have higher baseline levels and show training-induced increases in free testosterone, while older men still get a bump in total testosterone from resistance exercise, though the response is smaller.⁷

The acute testosterone spike after a single training session is temporary, usually returning to baseline within an hour or so. Whether those brief spikes matter for long-term muscle growth is still debated. Some researchers view the post-exercise testosterone surge as a meaningful anabolic signal; others argue that local muscle-level processes are more important than the temporary increase in circulating hormone. Either way, consistent training over weeks and months does appear to shift resting testosterone in a favorable direction in men, particularly when combined with adequate sleep and nutrition.

In women, the picture looks somewhat different. A 10-week study comparing high-intensity interval training and traditional resistance training in young women found that both types of exercise actually decreased testosterone over time, while estrogen increased substantially.⁸ That’s a reminder that the same exercise can produce opposite hormonal shifts depending on the person doing it.

Endorphins and Brain-Derived Neurotrophic Factor

The “runner’s high” is real, and beta-endorphins are a leading candidate for explaining it. These opioid peptides are released peripherally during exercise and have been explored as potential mediators of improved mood, reduced pain perception, and even the growth of new brain cells in the hippocampus, the brain region central to memory and learning.⁹ They’ve historically been dismissed because they’re released outside the brain and are too large to cross the blood-brain barrier easily, but researchers have identified possible routes by which endorphin signaling during exercise could still reach the hippocampus.

Alongside endorphins, exercise also boosts brain-derived neurotrophic factor (BDNF), a protein that supports the survival and growth of neurons. Animal studies have shown that voluntary running for several weeks significantly increases BDNF protein levels in the hippocampus.¹⁰ The mechanism appears to involve ketone bodies, specifically beta-hydroxybutyrate, which are produced during sustained exercise and can cross into the brain. This link between physical exertion and neuroplasticity is part of the growing case for exercise as a legitimate tool for brain health, not just cardiovascular fitness.

Myokines From Working Muscles

One of the more fascinating discoveries in exercise science is that skeletal muscle itself acts as an endocrine organ. When muscles contract, they release signaling molecules now known as myokines, which travel through the bloodstream and affect distant tissues.

The best-studied myokine is interleukin-6 (IL-6). After prolonged exercise, working muscles produce and release significant amounts of IL-6, which influences energy metabolism, stimulates muscle growth, and helps regulate the proliferative capacity of muscle stem cells.¹¹ The fact that IL-6 is also an inflammatory cytokine in other contexts caused some confusion early on, but the version released by exercising muscle behaves differently from the IL-6 produced during chronic inflammation. Exercise-derived IL-6 tends to drive anti-inflammatory effects downstream, which is part of why regular exercise reduces systemic inflammation over time even though a single workout temporarily raises certain inflammatory markers.¹²

Another myokine that has attracted attention is irisin, which is cleaved from a protein called FNDC5 on the surface of muscle cells during exercise. Irisin can convert white fat cells into a more metabolically active, brown-fat-like state, a process sometimes called “browning.”¹³ In animal models, irisin drives thermogenesis in white fat, suggesting it could partly explain how exercise improves metabolic health beyond just burning calories during the workout itself.¹⁴ Research on irisin in humans is still maturing, with debate about how much circulating irisin actually changes in response to different exercise types, but the concept of muscles as a hormone-releasing organ has reshaped how scientists think about the benefits of movement.

Appetite Hormones

If you’ve ever noticed that you feel less hungry right after a hard workout, there’s a hormonal explanation. Exercise suppresses acylated ghrelin, the form of ghrelin that stimulates hunger, while increasing peptide YY (PYY), a gut hormone associated with satiety.¹⁵ Both aerobic and resistance exercise suppress ghrelin, though PYY tends to rise more reliably with aerobic work.

This temporary appetite suppression has been confirmed in various experimental settings, including high-altitude simulations where exercise still managed to blunt hunger and reduce ghrelin despite the additional physiological stress.¹⁶ The effect is short-lived, usually fading within an hour or two. Whether these transient hormonal shifts lead to people eating less over the course of a day is harder to pin down, because appetite is influenced by so many other factors. But the hormonal signal itself is clear: hard exercise tells your gut “not now.”

Fluid Balance and Heart Hormones

Exercise puts pressure on the body’s fluid regulation systems, and the endocrine response reflects that. During prolonged endurance exercise like a marathon, plasma volume can drop substantially. In one study of well-trained runners, plasma volume fell by about 12% immediately after a marathon, and the fluid-regulating hormones arginine vasopressin (AVP, also known as antidiuretic hormone) and aldosterone spiked dramatically in response.¹⁷ AVP tells the kidneys to retain water, while aldosterone tells them to hold onto sodium. Both hormones were elevated immediately post-race but returned to normal within about a day, suggesting they are most active during the event itself and the immediate recovery window.

The heart also contributes to the hormonal picture. Atrial natriuretic peptide (ANP) is released when the walls of the heart’s atria are stretched, and exercise is one of the most common triggers for that stretch.¹⁸ ANP promotes sodium and water excretion and helps lower blood pressure, essentially counterbalancing some of the fluid-retaining signals from aldosterone. During cycling exercise, plasma ANP rose by over 200%, while brain natriuretic peptide (BNP) showed a more modest increase.¹⁹ ANP and BNP appear to be regulated by different aspects of cardiac function, with ANP linked more closely to atrial changes and BNP to ventricular function.

Thyroid Hormones and Bone Regulators

Thyroid hormones govern metabolic rate and heat production, so it makes sense that exercise affects them. The response is more nuanced than a simple rise. At moderate intensity, around the anaerobic threshold, thyroid hormones showed the most prominent changes, with T4, free T4, and TSH continuing to climb at higher intensities. However, T3 and free T3 actually started to fall once intensity exceeded that moderate threshold.²⁰ The reasons likely involve shifts in how the thyroid hormones are converted and cleared, including changes in liver and brown fat tissue enzyme activity that occur in the hours following a bout of exercise.²¹

Parathyroid hormone (PTH), which regulates calcium and phosphate balance, also responds to exercise. Physical activity changes circulating calcium and phosphate levels, and PTH adjusts accordingly. PTH also responds directly to exercise-induced myokines, creating a feedback loop between muscle activity and bone mineral homeostasis.²² This hormonal crosstalk helps explain the well-established link between weight-bearing exercise and bone density. The bones aren’t just passively stressed by loading; they receive chemical signals from the endocrine system that encourage mineral deposition and remodeling.

How Time of Day Influences the Hormonal Response

The same workout can produce different hormonal responses depending on when you do it. Cortisol follows a strong circadian rhythm, peaking in the early morning and falling through the day to its lowest levels around midnight. Exercise at 7 a.m. produces higher absolute cortisol peaks because baseline levels are already elevated. But exercise at midnight produces the largest relative increase, because it’s pushing cortisol up from its daily floor.²³ After late-night exercise, there’s even a rebound suppression of cortisol that doesn’t happen with morning or evening sessions.

Growth hormone, by contrast, doesn’t seem to care about the clock. Its response to exercise was similar regardless of whether the workout happened in the morning, evening, or middle of the night.²³ This means that if you’re concerned primarily about the anabolic GH signal from training, workout timing probably doesn’t matter much. If you’re trying to minimize cortisol exposure, though, evening workouts may produce a smaller absolute cortisol response than early-morning ones.

How the Menstrual Cycle Interacts With Exercise Hormones

For women, the menstrual cycle adds another layer to the hormonal response to exercise. Estradiol levels differ significantly between the early follicular phase and the luteal phase, roughly doubling in some studies.²⁴ This has led to speculation that women should time their training to their cycle, training harder during certain phases and backing off during others.

The evidence on whether those hormone fluctuations actually change exercise performance or metabolism in a practically meaningful way is, so far, thin. One study in well-trained women found that despite the expected differences in estradiol and progesterone between menstrual cycle phases, there were no differences in fat oxidation rates at any time point after resistance exercise.²⁵ In other words, the exercise itself was the dominant signal, not the cycle phase. This doesn’t mean the menstrual cycle is irrelevant to training, as symptoms like fatigue and cramping clearly matter for how workouts feel, but the hormonal fluctuations may not change the metabolic outcomes as much as some popular fitness advice implies.

How Chronic Training Reshapes Resting Hormones

Everything discussed so far has been about the acute hormonal response, what happens during and immediately after a single workout. Over weeks and months of consistent training, the baseline hormonal landscape itself shifts. A combined aerobic-and-resistance exercise program has been shown to reduce fasting insulin and improve insulin sensitivity, lower resting cortisol, raise resting growth hormone, and, in men, increase resting total testosterone.²⁶

The pattern with cortisol is interesting because it appears to depend on the type of training. Regular endurance exercise tends to result in slightly higher basal cortisol levels over time, likely reflecting the chronic demand of sustained aerobic work. Regular high-intensity interval training, on the other hand, tends to lower basal cortisol. The catecholamine response also dampens with repeated high-intensity work, meaning the body adapts so that the same effort produces less of a stress-hormone surge.²⁷ This is part of the broader phenomenon of training adaptation: what was once a major physiological stressor becomes routine, and the endocrine system’s alarm bells ring a little less loudly each time. For the single-bout growth hormone response, however, regular exercise doesn’t seem to blunt the peak, meaning trained individuals still get robust GH spikes from hard sessions even after months of training.

These chronic adaptations help explain why consistent exercise improves metabolic health in ways that go far beyond the calories burned during any individual session. Lower resting insulin and cortisol, improved insulin sensitivity, and a more favorable testosterone-to-cortisol ratio all point toward a metabolic environment that favors lean tissue maintenance and reduces disease risk over time.