A study in Austria examined whether aerobic capacity modulates psychophysiological responses to stress. The researchers found that people with higher aerobic capacity had lower heart rates during experimental stress conditions. The paper was published in Psychophysiology.
When a person faces a challenge, a demand, or perceives a threat, they experience stress. The body reacts with a stress response, a set of reactions that quickly increase alertness, heart rate, breathing, and the availability of energy. This response prepares the body for increased physical effort typically needed to fight a threat or flee from it.
The stress response is driven mainly by the sympathetic nervous system and a system involving the hypothalamus, pituitary, and adrenal glands. This system is called the hypothalamic–pituitary–adrenal (HPA) axis. The HPA axis releases the hormone cortisol, while the sympathetic nervous system stimulates the release of adrenaline. In the short term, this response can be useful because it prepares the body to confront danger or escape from it. Once the challenge has passed, the body returns to its normal state.
However, if the events that cause stress are intense, frequent, or never cease, so stress responses are initiated frequently or remain activated for too long, stress becomes chronic. Chronic stress can contribute to sleep difficulties, irritability, poor concentration, weakened immunity, cardiovascular problems, anxiety, depression, and various other health problems. People differ considerably in how strongly they react to the same event because stress depends partly on how a person perceives it and how able a person is to deal with the event. In some cases, a stressful day for one person can be a peaceful day for another.
Study author Peter Raidl and his colleagues hypothesized that physically fit individuals might be better able to cope with stress. More specifically, they hypothesized that physical fitness would be more relevant for coping with acute physical stressors than with psychosocial stressors. They conducted an experiment in which they tested whether physical fitness provides greater protection against stressors that include a physical component compared to stressors that are primarily social.
In this study, they operationalized physical fitness as aerobic fitness, assessed using a graded exercise test, and self-reported physical activity. Aerobic fitness is the ability of the heart, lungs, blood vessels, and muscles to supply and use oxygen efficiently during sustained physical activity. A graded exercise test is a treadmill or cycle test in which exercise intensity is gradually increased while heart rate, breathing, and sometimes oxygen consumption are measured.
Study participants were 59 healthy adults. Their average age was 27 years. Twenty-eight of them were women. They were required to maintain a regular sleep schedule for the time of the experiment, avoid traveling across multiple time zones in the weeks of testing, and refrain from intense exercise, supplement intake, or alcohol and other drugs for at least 24 hours before each experimental day. In addition, they were asked to abstain from caffeine and nicotine for 18 hours, and from eating, drinking caloric beverages, chewing gum, or brushing their teeth for 1 hour prior to testing.
Each participant took part in two experimental events on two different days at least a month apart. The experiments included completing a set of assessments at the start and then going through 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 (a task where participants perform mathematical calculations in their heads) performed in front of a committee. The purpose of the committee was to induce social stress. The committee comprised one male and one female interviewer, both dressed formally and instructed to maintain neutral facial expressions and body language. Interviews were conducted by an opposite-sex interviewer (also to increase stress).
The MAST combined elements of the TSST with having the participant dip their dominant hand in ice water multiple times (as a physical stressor). The participants held their hand in the water for 60 to 90 seconds each time and alternated this with a mental arithmetic task. After completing these tasks, participants completed follow-up assessments of their stress response. Study participants wore a heart rate monitor during the procedures.
Participants gave saliva samples at the start of the experiment, while they were anticipating stressors, and after each stress test protocol. At the beginning of each experimental day, participants completed an assessment of depression, anxiety, and stress symptoms (DASS-21). They completed an assessment of anxiety before and after each stress test, and rated their stress level at each saliva sampling. Participants were initially given a 2-week physical activity diary, but due to low completion rates, the authors relied on a physical activity questionnaire (IPAQ) to assess their activity levels. On a separate occasion, they completed the graded exercise test, allowing study authors to assess their aerobic capacity.
Results showed that participants with better aerobic fitness (higher peak oxygen uptake) tended to have a lower heart rate during both stress-induction situations. This association did not differ between TSST and MAST stress-induction procedures. No other outcome was associated with aerobic fitness.
“Aerobic fitness was linked to lower heart rate during the experimental sessions, indicating a modest cardiovascular advantage under acute stress. Contrary to our hypothesis, this effect did not differ between the two stress paradigms, suggesting that the influence of fitness was not specific to the type of stressor. Aerobic capacity, therefore, seems to reduce cardiovascular load during stressful situations in a general manner,” study authors concluded.
The study contributes to the scientific understanding of the links between physical fitness and stress response. However, it should be noted that the study used acute, laboratory-based stressors. Studies looking into coping with severe or chronic real-world sources of stress might yield different results.
The paper, “Does Aerobic Capacity Protect Against Stress? Insights From Two Stress-Induction Paradigms,” was authored by Peter Raidl, Anja Vogl, Aljoscha Dreisörner, Barbara Wessner, Urs M. Nater, and Robert Csapo.