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Exercise is a powerful form of stress relief. But biologically, exercise is stress.
This may be exactly why exercise is so protective. You're "practicing" the stress response, then training the body to recover, recalibrate, and return to baseline.
A new year-long study put this idea to the test. Researchers asked whether 12 months of aerobic exercise would make adults less reactive to stress at multiple levels. The answer was mostly no, with one important exception. The exercise group showed a meaningful reduction in cumulative cortisol exposure over months.
That might sound disappointing at first. But when paired with other recent studies, an interesting picture appears—the strongest stress-buffering effects of exercise may not come as a permanent, trait-like change after training. They may occur in the short window after a workout.
In other words, exercise may not make you “stress-proof.” But when timed correctly, it may change the physiological cost of the next stressful event.
In today's newsletter, we'll talk about why this happens and how to use deliberate exercise to make yourself more stress-tolerant.
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The study we’re covering today was built around the "cross-stressor adaptation" hypothesis—the idea that exposing the body to one type of stress can train it to better handle another.
Exercise is the obvious example. When you run, cycle, row, or do any form of sufficiently challenging aerobic exercise, you are deliberately putting your body under physiological stress. Heart rate rises. Blood pressure rises. Fuel is mobilized. And, especially at higher intensities, cortisol (the hormone most closely associated with the stress response) can rise, too.
That may sound like a bad thing. But it’s not. The stress response is not inherently harmful. It becomes harmful when it is excessive, repeated too often without recovery, or fails to shut off.
This is where exercise becomes interesting.
The cross-stressor adaptation hypothesis proposes that repeated bouts of exercise may train the body to become better at turning stress on and then turning it off. Exercise may act like controlled stress practice. The body learns how to respond and recover. Over time, that practice may cross over into other forms of stress—not just the physical stress of a workout, but the psychological stress of a deadline, a difficult conversation, a public presentation, or a chaotic day at work.
That was the “big” idea tested in this year-long trial.
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The "cross stressor adaptation" hypothesis. Gianaros et al. (2026). |
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Every week, Dr. Rhonda Patrick and the FoundMyFitness team distill the latest research into clear, actionable insights on health, longevity, and performance, delivered free to your inbox.
Training may not make you "stress-proof"
Researchers recruited 130 healthy adults between 26 and 58 years old and randomized them to either a year-long aerobic exercise intervention or a control group. Those in the exercise group were prescribed 150 minutes per week of aerobic exercise, split into two supervised 60-minute sessions and one 30-minute session performed at home or elsewhere. Most of the training was moderate intensity—around 60 to 75 percent of heart rate reserve, although participants could perform vigorous exercise at 75 to 85 percent of heart rate reserve during supervised sessions.
The intervention itself worked in the basic fitness sense. The program improved cardiorespiratory fitness, with VO₂ peak increasing by about 2 mL/kg/min.1 But this paper asked whether those fitness gains translate into a broad recalibration of the stress-response system.
To answer that, the researchers measured several layers of biology at once:
- Cardiometabolic and vascular risk markers, including triglycerides, total cholesterol, HDL cholesterol, HbA1c, and pulse-wave velocity (a measure of arterial stiffness)
- Neuroendocrine and autonomic markers, including hair cortisol and heart rate variability (HRV)
- Inflammatory markers, including IL-6 and ICAM-1
- Acute stress responses, including subjective distress, blood pressure reactivity, and brain activity during MRI-based stress and emotion tasks, during which the researchers tried to provoke stress and negative emotion while watching the brain and body respond in real time.
The idea was, if exercise truly trains the stress-response system, then after a year of aerobic training, the exercised brain might look less reactive under pressure, less responsive to negative emotional content, or better able to regulate emotion.
Surprisingly, it did not...
The intervention did not broadly alter most of the measured stress, emotion, autonomic, neural, inflammatory, vascular, or cardiometabolic outcomes.
But there was one important exception: hair cortisol decreased.
That matters because hair cortisol is different from a single cortisol measurement in blood or saliva. It reflects cumulative cortisol exposure over months, not just a momentary spike. The reduction in hair cortisol suggests that chronic aerobic training may still influence longer-term HPA-axis activity and the broader hormonal output of the stress system.
A "null result" might sound disappointing. Exercise is not effective at buffering stress? I think that would be the wrong takeaway.
A better interpretation is that one year of aerobic exercise did not produce generalized, across-the-board reductions in lab-measured stress reactivity or emotion regulation in healthy midlife adults.
And that brings us to the more interesting question: Were the researchers looking at the wrong time frame?
A year of training may not permanently flatten the brain and body’s response to every lab-based stressor. But acute bouts of exercise may reduce stress reactivity in the immediate post-exercise window. In other words, exercise works more like a temporary physiological buffer that's strongest in the minutes or hours after the workout, when the body is actively shifting from activation into recovery.
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Hair cortisol levels before and after the year-long intervention in the exercise (blue) and control (yellow) groups. |
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In a few of my Q&A episodes, I've discussed how other physiological stressors, including sauna and intermittent fasting, benefit us by activating the body's built-in stress-response systems.
Q&A #46
- (25:28) Why sauna use significantly improves cardiovascular health
- (29:17) How heat shock proteins shield the brain from Alzheimer's
- (30:30) Do hot baths also boost heat shock proteins?
- (31:10) Does sauna use effectively lower inflammation?
- (32:14) Can heat stress elevate brain-derived neurotrophic factor (BDNF)?
Q&A #43
- (22:57) How does fasting enhance cellular repair?
- (24:55) Are there unique benefits of prolonged fasting for healthy individuals?
- (25:37) How soon does autophagy start during a prolonged fast?
- (26:28) How prolonged fasting benefits immune and stem cells
- (26:42) How much prolonged fasting is too much for healthy individuals?
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The post-workout stress-buffering window
That question of whether exercise affects stress biology most strongly in the short window after a workout has been tested more directly in acute exercise studies.
One study asked a simple but mechanistically important question: Can a single bout of aerobic exercise change the cortisol response to a later psychological stressor?2
Researchers recruited 83 healthy young men, average age about 21, and randomized them to perform 30 minutes of treadmill exercise at one of three intensities: light, moderate, or vigorous. Then, 45 minutes later, participants underwent the Trier Social Stress Test, one of the most widely used laboratory stressors, involving public speaking and mental arithmetic in front of evaluators. Participants who performed vigorous exercise had a smaller cortisol response to the stressor than those who exercised at lower intensities. They:
- produced less total cortisol,
- had a lower peak cortisol response,
- showed less cortisol reactivity, and
- recovered faster toward baseline.
In other words, the harder workout produced a larger cortisol response during exercise, but a smaller cortisol response to the psychological stressor that came afterward. This is an important distinction. The benefit was not that vigorous exercise kept cortisol low the entire time. It did the opposite at first. It raised cortisol during the workout, then appeared to blunt the response to the later stressor.
That is a very different way of thinking about stress resilience. The goal is not to avoid activating the stress system. The goal is to activate it in a controlled way, recover from it, and perhaps become less reactive to the next challenge.
Another study suggests this acute buffering effect may extend beyond cortisol to the cardiovascular system.3
In that study, 40 young adults completed two experimental sessions in a randomized crossover design. In one session, they experienced a psychological stress task by itself. In the other, they performed 10 minutes of aerobic exercise at 70 percent of VO₂max (moderate-to-vigorous intensity exercise) before the stress task.
After the brief exercise bout, participants had lower blood pressure and heart rate responses to the stressor. They also reported lower physical sensations of anxiety, such as bodily tension or arousal, even though they rated the stressor itself as more intense.
At first glance, these acute studies seem to contradict the year-long trial. But the cleaner way to interpret these findings is to separate training effects from state effects.
- Training effects are the longer-term adaptations that accumulate after weeks, months, or years of exercise: improved cardiorespiratory fitness, better metabolic health, and perhaps lower cumulative cortisol exposure.
- State effects are the temporary changes that occur after a single workout: shifts in hormones, autonomic tone, blood pressure regulation, mood, arousal, and recovery biology.
Exercise does both.
The chronic effect may show up as improved fitness and lower cumulative stress-hormone exposure over time. The acute effect may show up as a temporary stress-buffering window—a period after exercise when the body is better able to absorb the next psychological challenge without producing as large a physiological response.
That means cross-stressor adaptation may not be a simple, permanent switch where fit people become universally less reactive to stress. It may be time dependent (strongest soon after exercise), intensity-dependent (vigorous exercise appears more effective than light exercise), and context-specific (most of us do not experience stress inside a laboratory or fMRI machine, but rather, in real life).
(In the clip below, I discuss the impressive brain benefits of vigorous aerobic exercise).
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Final thoughts
This newsletter is especially meaningful to me because it highlights a strategy I’ve used for nearly two decades.
I’ve always found that vigorous aerobic exercise, when performed before a cognitively demanding task or something I expect to be stressful (a big presentation, an interview, a podcast, or an intense study session) helps me think more clearly and feel less physically overwhelmed. The bodily sense of stress feels different. I really do think that a hard workout makes the rest of the day easier.
And that is what makes this research so practical.
For a predictable stressor, a short bout of aerobic exercise beforehand may help reduce the body’s physiological response to that stressor. Based on the acute studies, the protocol is:
10 to 30 minutes Moderate-to-vigorous or vigorous aerobic exercise (think hard cycling, running, incline walking, rowing, or intervals) Performed roughly 30 to 60 minutes before the stressful event
Exercise probably isn't the only intervention that has this acute stress-buffering effect. Another one of my favorite strategies, sauna, mimics the effects of exercise and also induces a controlled but measurable stress response in the body. I'd use it in the same way as exercise before predictable stressors (you can read about the wide-ranging benefits of sauna on our Sauna topic page).
The key is not to exhaust yourself. It is to deliberately engage stress biology in a controlled, time-limited way, and then recover.
That recovery period matters. A cooldown, hydration, and a little time for your breathing and heart rate to settle are probably part of the effect. The goal is not to walk into a stressful event gasping and depleted.
This does not mean every stressful event should be preceded by a hard workout. Vigorous exercise is still a stressor, and it needs to be used intelligently. If you are sleep-deprived, overtrained, sick, under-fueled, or already stretched thin, piling on more intensity may not be the right move.
The benefit likely depends on the transition from activation to recovery.
When used well, exercise is one of the most accessible tools we have.
It may not eliminate stress. But it may change how much that stress costs the body.
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Warm regards
— Rhonda and the FoundMyFitness team
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