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UBC Theses and Dissertations

Acute exercise alters cortisol responses to psychosocial stress : a mechanism of exercise intensity Caplin, Adam Marc


While the body’s stress system plays an adaptive role in helping humans respond to challenging and threatening stimuli, frequent or prolonged exposure to difficult stressors can detriment both physical and psychological health, and lead to the eventual development of chronic diseases. Though chronic activation of the stress system damages health, physical activity can mitigate the psychological and physiological stress response in daily life, benefiting long term health. While research has examined the effects of fitness level and frequent physical activity on various features of the human stress response, little is known regarding the effect of a single bout of aerobic activity on the physiological reactivity to an acute stressor (i.e. the increasing response over time), and the recovery, or return, back to baseline. The current study thus investigated two research questions: (1) whether the effects of exercise on the Hypothalamic Pituitary Adrenal (HPA) axis response (i.e. reactivity and recovery) to an acute stressor depends on the intensity at which a bout of exercise is performed, and (2) whether associations exist between the HPA-axis outcomes of exercising at various intensities and the cortisol responses to a subsequent psychosocial stressor, delineating a biological mechanism of the stress-buffering effects of exercise. These questions were addressed by constructing mixed-effects models, with between person and within person effects, in which eighty-three 18- to 30-year-old men were randomized to exercise at either 30%, 50% or 70% of their heart rate reserve and then underwent a psychosocial stress task. ANCOVA and Multilevel Growth Curve Analysis determined that more intense exercise elicited dampened cortisol responses to the stress task, marked by lower total cortisol levels, diminished cortisol reactivity and faster recovery to baseline values, as compared to less intense exercise. Moreover, exercise itself elicited a cortisol response proportional to the intensity at which it was performed, and this exercise-associated HPA-axis response was inversely proportional to the cortisol response to the subsequent stress task. This study concluded that exercise-intensity dampens the HPA-axis stress response in a dose dependent manner with mounting evidence that the cortisol released from exercising intensely helps to suppress the subsequent cortisol response to a stressor.

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