Exercise triggers the release of several hormones at once, not just one. The mix changes depending on how hard you’re working, how long you keep going, and what type of exercise you’re doing. Some hormones spike within seconds to fuel your muscles, others build gradually to manage blood sugar, and a few only appear when you push past a certain intensity threshold. Here’s what’s actually happening inside your body during a workout.
Adrenaline and Norepinephrine: The Instant Responders
The moment you start exercising, your sympathetic nervous system fires up and releases two closely related hormones: epinephrine (adrenaline) and norepinephrine. These are the fastest-acting hormones in the exercise response. They increase your heart rate, widen the blood vessels feeding your working muscles, and redirect blood away from organs that don’t need it right now, like your digestive system.
The harder the exercise, the more of these hormones your body produces. The trigger works partly through pressure sensors in your arteries. When your muscles demand more blood flow, the surrounding blood vessels dilate, which drops your blood pressure momentarily. Your body detects this and responds by ramping up adrenaline and norepinephrine to constrict other blood vessels and keep pressure stable. A second trigger comes from the muscles themselves: nerve endings in contracting muscle fibers send signals back to the brain, calling for more sympathetic activation.
Of the two, norepinephrine dominates during most exercise. A massive spike in adrenaline specifically only happens when exercise is intense enough to cause a significant drop in blood sugar.
Endorphins: Harder Than You Think to Trigger
Endorphins get the most attention, largely because of the “runner’s high” concept, but they’re surprisingly difficult to trigger. Research on trained endurance athletes found that plasma endorphin levels didn’t change at all during exercise at 50%, 58%, 69%, or even 80% of maximum effort. It took exercise at 92% of maximum capacity before endorphin levels rose significantly, roughly tripling from resting values. At 98% of max effort, endorphin concentrations increased more than fivefold.
This means a casual jog or moderate bike ride probably isn’t producing the flood of endorphins many people assume. The threshold appears to be anaerobic exercise, the kind where you’re breathing so hard you can barely talk and your muscles are burning with lactic acid. If you’ve ever felt that wave of calm and euphoria after an all-out sprint session or a grueling hill workout, that’s likely the real endorphin effect. Lighter exercise still improves mood, but through other chemical pathways.
Growth Hormone: The Repair Signal
Human growth hormone plays a central role in tissue repair, fat metabolism, and muscle recovery. Your body releases it in response to exercise, but the details matter. You need to exercise above your lactate threshold (the point where your muscles start burning) for a minimum of about 10 minutes to get a meaningful increase in circulating growth hormone.
Interestingly, sustained aerobic exercise can outperform short sprints for growth hormone release. In one study, 30 minutes of cycling at 70% of peak capacity produced a greater growth hormone response than a single 30-second all-out sprint. For women, exercising at 75% of peak capacity for at least 10 minutes is enough to trigger a significant response. The takeaway is that moderate-to-hard effort sustained for a reasonable duration beats brief, explosive bursts when it comes to this particular hormone.
Growth hormone levels also help explain why exercise reduces belly fat. Higher-intensity workouts led to greater reductions in deep abdominal fat compared to moderate exercise, even when the total calories burned were matched. Growth hormone likely plays a role, though other factors contribute too.
Cortisol: The Stress Hormone With a Purpose
Cortisol often gets labeled as the “bad” stress hormone, but during exercise it serves a useful function. It helps mobilize energy stores, reduces inflammation, and supports your body’s ability to sustain effort. After a hard workout, cortisol levels stay elevated for roughly 150 minutes before returning to baseline.
The time of day you exercise affects the cortisol response. Working out late at night produces the largest spike in cortisol relative to your normal levels at that hour, since cortisol is naturally at its lowest around midnight. After a late-night session, the body also shows a rebound suppression, where cortisol drops below normal for about 50 minutes before stabilizing. This doesn’t happen with morning or evening workouts. For most people exercising at typical hours, the post-workout cortisol bump is modest and resolves on its own.
Insulin and Glucagon: Blood Sugar Management
While most exercise hormones go up, insulin goes down. Your body actively suppresses insulin secretion during physical activity so that stored glucose can be released into the bloodstream and used as fuel. This suppression is driven by the same adrenaline-related pathways that rev up your heart rate.
At the same time, glucagon (insulin’s counterpart) rises to signal the liver to release its glucose reserves. This insulin-glucagon seesaw is what keeps your blood sugar stable during a long run or cycling session, even though your muscles are burning through glucose at a high rate. It’s also why exercise is so effective at improving blood sugar control over time: regular workouts train this system to respond more efficiently.
Testosterone: A Brief Post-Workout Spike
Resistance training, specifically lifting heavy weights, triggers a temporary increase in testosterone. In men, testosterone and free testosterone typically rise within 15 to 30 minutes of starting a session and return to resting levels within an hour of finishing. This acute spike is thought to support muscle protein synthesis and recovery in the hours that follow.
In women, the testosterone response to resistance exercise is minimal or nonexistent. Women build strength and muscle through other hormonal and cellular pathways, which is why resistance training is effective regardless of sex, even though the testosterone response differs dramatically.
Irisin: The Calorie-Burning Myokine
Your muscles themselves function as a hormone-producing organ during exercise. One of the key signaling molecules they release is irisin, classified as a “myokine” because it originates from muscle tissue. Irisin’s most notable effect is converting white fat (the storage kind) into brown fat (the calorie-burning kind). Brown fat generates heat and burns energy, which is one reason regular exercisers tend to have more metabolically active fat tissue over time.
BDNF: Exercise for Your Brain
Exercise also triggers the release of brain-derived neurotrophic factor, a protein that supports the growth and survival of brain cells. BDNF is essentially fertilizer for your nervous system, strengthening existing connections between neurons and encouraging the formation of new ones.
Intensity matters here too. A single session of high-intensity aerobic exercise increased BDNF concentrations by an average of about 2.5 ng/mL, with ongoing high-intensity training programs producing even larger gains of roughly 3.4 ng/mL. Low-intensity exercise, on the other hand, actually decreased BDNF levels slightly, and moderate intensity produced mixed results. This pattern mirrors what happens with endorphins: if you want the brain benefits, you need to push reasonably hard.
The practical picture is that exercise doesn’t release one magic hormone. It orchestrates a coordinated response across your entire endocrine system: fueling muscles, stabilizing blood sugar, managing stress, triggering repair, burning fat, and protecting your brain. The intensity and duration of your workout determine which parts of this response are strongest, with harder efforts unlocking hormonal benefits that lighter activity simply doesn’t reach.