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The hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system (SNS) play roles in the stress response and the production of glucocorticoids (cortisol) and epinephrine, respectively. Exercise is a form of stress, requiring greater energy supply in somatic tissues, and activates both the HPA axis and SNS. Glucocorticoids promote gluconeogenesis - glucose synthesis - in the liver, while epinephrine stimulates ATP production. Exercise is not associated with fear or threat like psychological stress, so there must be some underlying differences.

Exercise and stress response

Both psychological and physical stress (from exercise) activate stress response via the HPA axis and SNS, but only psychological stress is associated with fear. Furthermore, exercise is shown to have a beneficial effect on mood. Subjects who are endurance-trained have lower sensitivity to glucocorticoids, suggesting that exercise leads to an adaptation to the stress response. Exercise may provide negative feedback to the HPA axis.

Psychological stress vs. Physical stress

Major depressive disorder is linked to an imbalance in levels of cortisol, a hormone involved in the stress response. Beserra et al. (2018) conducted a meta-analysis of 463 studies investigating the connection between exercise and cortisol. They found that exercise leads to a moderate reduction in cortisol. However, discrepancies in methods for measuring cortisol (urine, saliva, plasma) and exercise type or frequency made it difficult to reach a definite conclusion.

Exercise and cortisol

Prolonged physical exercise may lead to a reduced physiological reaction to stressors. For example, a study involving rats that exercised for six weeks found that their hypothalamic-pituitary-adrenal (HPA) axis, a key part of the stress response system, became less responsive to mild stressors.

Exercise and Reduced HPA Axis Responsiveness

A person is engaged in a vigorous 30-minute run. Which of the following statements best analyzes the distinct roles of the two primary physiological stress response systems activated to meet the body's increased energy demands?

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