It Works! How Intense Exercise Reduces Post-Workout Stress Response

By Chris Carmichael,
Founder and Head Coach of CTS

My coaches and I work with many athletes leading high-pressure careers, including C-suite executives, entrepreneurs, first responders, and medical professionals. Others are experiencing life-altering levels of stress from failing relationships, long-term caregiving for sick loved ones or aging parents, or grief from losing loved ones. There is nothing new about using exercise as a means of coping with and alleviating stress derived from other areas of life, but a recent study piqued my interest because it aimed to determine whether a single bout of intense exercise could mitigate the ‘fight or flight’ stress response to a subsequent psychosocial challenge. In other words, can a hard workout make your afternoon meeting – or holiday travel or Christmas Eve with your in-laws – feel less stressful?

Human Stress Response

When humans experience stress – whether that’s voluntary exercise, being chased down an alley, or public speaking – there is a physiological response that immediately activates the sympathetic nervous system, leading to the release of epinephrine and norepinephrine and a subsequent increase in heart rate and alertness. Within seconds, the hypothalamic-pituitary-adrenal axis (HPA axis) is activated. The hypothalamus (a region of the brain just above the brainstem) signals the pituitary gland, which secretes a hormone into the bloodstream that subsequently signals the adrenal glands on top of your kidneys to secrete glucocorticoids like cortisol.

Cortisol is a hormone that gets you physically ready to fight or flee. In response to a stressor, elevated levels of cortisol in the bloodstream lead to increased blood pressure, increased cardiac output, and increased levels of blood glucose. At the same time, it reduces priority and resources available for nonessential functions – or at least functions that aren’t essential right now.

Being able to ramp up the human stress response is important, and so is being able to shut it down. There is theorized negative feedback loop that responds to increased circulating levels of glucocorticoids by signaling the hypothalamus and pituitary gland to downregulate the signals to the adrenal glands (Zschucke et al., 2015). The feedback loop seems to become desensitized in people who are exposed to frequent stressors (physical and/or psychological) for prolonged periods of time, leading to chronically elevated levels of circulating cortisol, which may be associated with the development of depression, chronic disease, memory impairment, and compromised immune function.

Consistent exercise, which is a stressor in itself and activates the HPA axis, is helpful for maintaining normal daily cortisol rhythms and keeping the negative feedback loop functioning well. In other words, people who exercise consistently experience an increase in cortisol levels but also have sensitive mechanisms for bringing cortisol levels back down.

What good is a single hard bout of exercise?

Anecdotally, think about how you feel in the hours after a hard interval workout. Are stressful situations easier to deal with? Do you get less flustered or frustrated in meetings or tense conversations at home? Do complicated tasks seem less intimidating? For a long time I thought it might have something to do with fatigue, that I was too tired to get riled by a work-related stressor. What is more likely is “cross-stressor adaptation”, which theorizes that a repeated challenge of one type sensitizes the HPA axis response to similar stressors (Sothmann 1996). In other words, exercise activates the HPA axis and its negative feedback loop, and then the HPA axis activation to a subsequent non-exercise stressor is blunted.

Researchers in the School of Kinesiology at the University of British Columbia wanted to investigate whether there was a dose-response relationship between exercise intensity and cortisol response to a subsequent psychosocial challenge. If any exercise is good, is hard exercise better?

A group of 83 young male subjects (average age was 21 but there were a few faculty members included) were divided into three groups: Light exercise intensity (20-39% of heart rate reserve), moderate exercise intensity (40-59% of HRR), and Vigorous (60-84% HRR). One limitation of this study is that it excluded female subjects “to control for fluctuations in salivary cortisol levels resulting from different phases of the menstrual cycle”. Subjects were instructed to walk or run at their prescribed intensity level for 30 minutes, cool down with 5 minutes of walking, and then sit for 45 minutes. They then completed the Trier Social Stress Test (TSST), which consists of public speaking and mathematics performed in front of a panel of evaluators. After the TSST, subjects again sat for 70 minutes. Throughout the experimental protocol, 14 saliva samples were taken and tested for levels of salivary cortisol.

Read complete study

Findings

Researchers found, predictably, that subjects who exercised vigorously experienced larger overall cortisol responses (increases) to the exercise portion. After the 45-minute rest period, the Vigorous group started the TSST with higher salivary cortisol levels than the moderate or light groups, but those levels were less reactive and reached lower peak levels compared to the Moderate or Light groups. Similar results were found between the moderate and light groups. The stress response to the psychosocial challenge (comparable to your meeting, tense convo with a loved one, or complicated task) was lessened by training harder 45 minutes earlier.

Source

Practical Application

Now, the study was small, excluded female subjects, and didn’t investigate how differences in exercise modality or duration could affect the cortisol response to post-exercise stressors, so we can’t conclude that hard interval workouts are the key to getting a promotion, closing that big deal, or saving your marriage. But if you, like me, always felt there was a connection between a good, hard workout and better outcomes in stressful situations later that same day, perhaps it was more than a hunch.

If you habitually schedule training after your workday as a means of dissipating or burning off stress accumulated during the day, conduct your own experiment. Switch it up and put a hard mid-day workout into your schedule before a stressful – but routine – activity in the afternoon. Because it’s an activity you do regularly, you’ll be able to compare how stressed you feel normally to how you feel performing the same activity after a hard workout.

References:

Caplin A, Chen FS, Beauchamp MR, Puterman E. The effects of exercise intensity on the cortisol response to a subsequent acute psychosocial stressor. Psychoneuroendocrinology. 2021 Sep;131:105336. doi: 10.1016/j.psyneuen.2021.105336. Epub 2021 Jun 18. PMID: 34175558.

Sothmann MS, Buckworth J, Claytor RP, Cox RH, White-Welkley JE, Dishman RK. Exercise training and the cross-stressor adaptation hypothesis. Exerc Sport Sci Rev. 1996;24:267-87. PMID: 8744253.

Zschucke E, Renneberg B, Dimeo F, Wüstenberg T, Ströhle A. The stress-buffering effect of acute exercise: Evidence for HPA axis negative feedback. Psychoneuroendocrinology. 2015 Jan;51:414-25. doi: 10.1016/j.psyneuen.2014.10.019. Epub 2014 Oct 25. PMID: 25462913.