A new year-long study has found that regular aerobic exercise lowers long-term levels of key stress hormones, which may help prevent heart disease and mood disorders. Published in Sports Health Science JournalThis clinical trial demonstrates how meeting standard physical activity guidelines can benefit our underlying stress biology. These results suggest that sweating provides sustained physiological relief from chronic stress.
Peter Gianaros, a psychology researcher at the University of Pittsburgh, led the study along with a team of health and neuroscience experts. The research team wanted to understand whether training the body to cope with physical exertion also trains the brain and body to cope with mental pressure. They designed a study to monitor these biological adaptations over a one-year period.
When a person exercises, their heart rate increases and their body experiences temporary physical stress. Over time, regular exercise improves the efficiency with which your cardiovascular system copes with this physical load. Researchers have proposed a concept called the cross-stressor adaptation hypothesis to explain how this works.
This hypothesis suggests that the biological upgrades gained from regular physical activity may help the body manage emotional and psychological stress. If your cardiovascular system is healthier, you may react less strongly to an argument at work or a frustrating traffic stop. The research team set out to test this idea by looking at several biological markers, including cortisol.
The cross-stressor adaptation hypothesis also suggests that working out changes the physical structure of the brain. Regular physical activity can induce neuroplasticity, the ability of the brain to rewire itself. This rewiring may stabilize the brain circuits that control the autonomic nervous system.
The autonomic nervous system acts as a control center for involuntary bodily functions such as heart rate and digestion. By increasing the efficiency of this system, aerobic fitness could theoretically calm our biological responses to negative emotions.
Cortisol is the main stress hormone in humans. It plays a role in regulating metabolism, immune response, sleep cycles, and overall mood. Long-term exposure to high levels of cortisol increases the risk of heart disease and metabolic disorders.
Most physiological tests measure cortisol in saliva or plasma. These methods capture only a short snapshot of stress at a particular moment in time. However, cortisol also accumulates in human hair as the hair grows from the scalp.
By testing hair clippings, researchers can measure systemic cortisol exposure over several months. This retrospective measurement gives scientists a broader picture of a person’s chronic stress burden. Gianaros and his team used this technique to see if physical training changes this long-term accumulation of hormones.
The clinical trial involved 130 healthy adults between the ages of 26 and 58. None of the participants exercised regularly before the study began. The researchers used a randomization process to divide these participants into two different groups.
One group was assigned to complete 150 minutes of moderate-to-vigorous aerobic exercise each week for one year. This routine may include brisk walking, jogging, or using a stationary bike. Participants took part in supervised training sessions and wore heart rate monitors to track their physical activity.
To monitor their progress, participants in the exercise group utilized wearable heart rate sensors. For the first six weeks, I aimed to keep my heart rate at a moderate intensity. After this initial adjustment period, they were encouraged to increase the intensity of their training to a more vigorous level. A certified trainer checked in regularly to ensure everyone was exercising safely.
The second group served as the health information management group. These people received general educational materials about blood pressure and body composition. They were asked not to change their usual physical activity habits throughout the year.
Throughout the year, researchers tracked multiple biological and psychological markers in a laboratory setting. They took fasting blood samples to check systemic inflammation, blood sugar levels and cholesterol. They also measured artery stiffness by tracking how fast pulse waves traveled from the heart to the calves.
The researchers also monitored heart rate variability, which tracks the small time differences between successive heartbeats. High heart rate variability usually indicates that the nervous system is relaxed and adaptable. Low fluctuations often indicate increased physical or mental stress.
In addition to these cardiovascular tests, participants also underwent testing within a magnetic resonance imaging machine. While inside the brain scanner, they completed frustrating psychological tasks meant to trigger a temporary stress response. These tasks involved processing conflicting information and receiving negative feedback within tight time limits.
During a separate scanner task, participants viewed upsetting images selected from a standardized psychological database. They were asked to actively try to change the way they felt about the image by reframing the negative scene into something more positive. This enabled the research team to monitor brain activity, blood pressure changes, and ability to regulate emotions in real time during moments of mental stress.
After a year of observation, the researchers found clear differences in the hair samples they collected. Participants who completed a weekly aerobic exercise routine showed a decrease in accumulated hair cortisol compared to the control group. Through a year of brisk walking and jogging, I was able to reduce my systemic exposure to this stress hormone.
Gianaros explained the potential significance of this biological change. He said: “The effects of exercise on long-term cortisol levels may be one of the mechanisms and benefits of exercise to protect against some diseases and some mental health conditions, but further research is needed to fully explore this possibility.”
The remaining biological and psychological markers showed no obvious improvement. There were no significant changes in cholesterol, blood sugar levels, or markers of systemic inflammation in the exercise group. Small changes in these specific variables were not statistically significant.
The difference in mental stress responses between the exercise and control groups during the brain scan task was also not statistically significant. A year of aerobic training did not seem to change how the participants’ brains and blood pressure responded to sudden acute stressors. Their self-reported emotional responses to negative images remained roughly the same as before the trial.
The research team pointed to several reasons why the physical activity routine may not have improved all the health markers measured. One of the main factors was the study’s strict enrollment criteria. To ensure safety, researchers selected only adults who were extremely healthy and had no underlying health conditions.
Because the participants were already in good health, their biological markers may not have had much room for improvement. This ceiling effect often makes it difficult to detect small changes in cardiovascular disease risk factors in healthy populations. This clinical trial was also conducted during the early stages of the global pandemic.
Another limitation of the clinical trial included the lack of a questionnaire on daily life stressors. The researchers did not ask participants to track daily mood swings or environmental pressures at home. Lacking this background, it is difficult to know whether reductions in hair cortisol fully reflect reductions in daily psychological stress.
Disruptions related to the pandemic resulted in a higher dropout rate of participants than the team had originally anticipated. Smaller final group sizes can limit the mathematical ability to detect subtle biological changes. It remains unclear whether differences in the amount of physical activity cause broader biological changes.
Future studies may include more people, including those who already have pre-existing health conditions such as high blood pressure or metabolic disorders. Testing workouts of varying intensities may reveal exactly how much exercise you need to optimize your stress biology. Examining these variables will help scientists create a more detailed map of how physical fitness protects the brain and body.
The study, “Effects of a 1-year aerobic exercise intervention on neuroendocrine, autonomic, and neural correlates of stress, emotion, and cardiovascular disease risk in middle-aged adults,” was authored by Peter J. Gianaros, Lu Wan, Mia K. DeCataldo, Cristina Molina Hidalgo, Mark R. Scudder, George Grove, Abigail Shell, Chae Ryon Kang, and E. Lydia. Wu Chun, Anna L. Marsland, Thomas W. Kamarck, Javier Lacero, and Kirk I. Erickson.
