A study conducted in Austria investigated whether aerobic capacity modulates psychophysiological responses to stress. Researchers found that people with higher aerobic capacity had lower heart rates under experimental stress conditions. The paper is psychophysiology.
People experience stress when they face challenges, demands, or perceive threats. The body responds with a stress response, a series of reactions that rapidly increase alertness, heart rate, breathing, and energy availability. This response prepares the body for the increased physical effort normally required to fight or escape a threat.
The stress response is primarily triggered by the sympathetic nervous system and a system involving the hypothalamus, pituitary gland, and adrenal glands. This system is called the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis releases the hormone cortisol, and the sympathetic nervous system stimulates the release of adrenaline. In the short term, this response can be helpful because it prepares the body to face or escape danger. Once the ordeal has passed, the body returns to its normal state.
However, stress becomes chronic when the stress-causing events are intense, frequent, or never stop, and the stress response begins frequently or remains activated for too long. Chronic stress can lead to difficulty sleeping, irritability, difficulty concentrating, a weakened immune system, cardiovascular problems, anxiety, depression, and a variety of other health problems. Because stress depends in part on how a person perceives it and how well he or she is able to cope with the event, people vary greatly in how strongly they react to the same event. Sometimes what is a stressful day for one person can be a peaceful day for another.
Study author Peter Leidle and colleagues hypothesized that physically healthy people may be better able to cope with stress. More specifically, they hypothesized that physical fitness might be more relevant for coping with acute physical stressors than psychosocial stressors. They conducted an experiment to test whether physical fitness provides a better protective effect against stressors that have a physical component compared to primarily social stressors.
In this study, they operationalized physical fitness as aerobic exercise and assessed it using graded exercise tests and self-reported physical activity. Aerobic fitness is the ability of the heart, lungs, blood vessels, and muscles to efficiently supply and use oxygen during sustained physical activity. A graduated exercise test is a treadmill or cycle test that gradually increases the intensity of your exercise while measuring your heart rate, breathing, and sometimes oxygen consumption.
Study participants were 59 healthy adults. Their average age was 27 years. Of these, 28 were women. They were required to maintain a regular sleep schedule during the experiment, avoid traveling across time zones during the weeks leading up to the experiment, and refrain from strenuous exercise, taking supplements, or taking alcohol or other drugs for at least 24 hours before each experiment day. In addition, participants were asked to refrain from caffeine and nicotine for 18 hours, and to refrain from eating, drinking, consuming caloric beverages, chewing gum, or brushing their teeth for one hour before the test.
Each participant participated in two experimental events on two different days separated by at least 1 month. The experiment involved first completing a battery of assessments and then passing either the Trier Social Stress Test (TSST) or the Maastricht Acute Stress Test (MAST). The TSST consisted of a 5-minute mock job interview followed by a 5-minute mental arithmetic task (in which participants performed mathematical calculations in their heads) in front of a committee. The purpose of the committee was to induce social stress. The panel consisted of one male and one female interviewer, both of whom were formally dressed and instructed to maintain a neutral facial expression and body language. Interviews were conducted by interviewers of the opposite sex (also to increase stress).
MAST combined elements of the TSST with having participants immerse their dominant hand in ice water multiple times (as a physical stressor). Participants placed their hands underwater for 60 to 90 seconds each time, alternating this with mental arithmetic tasks. After completing these tasks, participants completed a follow-up assessment of their stress responses. Study participants wore heart rate monitors during the procedure.
Participants provided saliva samples at the beginning of the experiment, while anticipating stressors, and after each stress test protocol. At the beginning of each experimental day, participants completed the Depression, Anxiety, and Stress Symptom Assessment (DASS-21). They completed anxiety assessments before and after each stress test and assessed their stress levels at the time of each saliva collection. Participants were initially given a two-week physical activity diary, but due to low completion rates, the authors utilized the Physical Activity Questionnaire (IPAQ) to assess activity levels. On another occasion, they completed a graded exercise test that allowed study authors to assess their aerobic capacity.
Results showed that participants with better aerobic fitness (higher peak oxygen uptake) tended to have lower heart rates in both stress-inducing situations. This association did not differ between the TSST and MAST stress induction procedures. No other outcomes were associated with aerobic fitness.
“Aerobic fitness is associated with lower heart rate during experimental sessions, indicating a modest benefit for the cardiovascular system under acute stress. Contrary to our hypothesis, this effect did not differ between the two stress paradigms, suggesting that the effects of fitness are not specific to the type of stressor. Therefore, aerobic fitness appears to reduce cardiovascular load under stressful conditions in a general way,” the study authors concluded.
This study contributes to the scientific understanding of the link between physical fitness and stress response. However, it should be noted that this study used a laboratory-based acute stressor. Studies examining coping with severe or chronic real-world stressors may yield different results.
The paper “Does aerobic capacity protect against stress? Insights from two stress-inducing paradigms” was authored by Peter Raidl, Anja Vogl, Aljoscha Dreisörner, Barbara Wessner, Urs M. Nater, and Robert Csapo.
