Effects of Different Features of a Single Bout of Exercise on Neurobiological Activation and Recovery Following Induction of Psychological Threat

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Stressors can be physical (e.g. exercise, cold exposure) or psychological in (e.g. arguments). Two neurobiological networks are activated in response to stressors - the sympathomedullary pathway (SAM-p) and hypothalamus-pituitary-adrenal axis (HPA-a) - to coordinate physiological, cognitive, and behavioural responses necessary to manage the stressor. The cross-stressor adaptation hypothesis suggests that repeated experiences with the same type of stressor lead to a reduced, or habituated, neurobiological response over time to that same stressor, and either habituated or sensitized (i.e. more pronounced) responses to stressors dissimilar in nature. In human research, the majority of studies have focused on two heterotypic stressors, namely physical exercise and psychological threat, and the majority of these studies induced threat in the lab to test differences between physically active and inactive adults. These studies make the assumption that apparent differences in neurobiological responses to psychological threat result from the repeated exposure to bouts of exercise in physically active adults. To better understand the underlying mechanisms, however, research is required that examines the immediate neurobiological responses to a single bout of exercise and their resulting effects on neurobiological responses to psychological threat induced by an acute psychosocial stressor. Our preliminary results from our first study tackling this question demonstrate that higher levels of cortisol (i.e. greater HPA-a activation) in response to vigorous exercise, as compared to moderate or light, mediates the reduced cortisol response to an acute psychosocial stressor that follows 45 minutes later. No differences were evidenced in SAM-p activation. The purpose of the current Discovery Grant is to outline and implement a series of rigorous experiments to understand the complex biological effects of an acute bout of exercise when intensity (moderate, vigorous, high) and mode (continuous, interval; aerobic, resistance) are manipulated and how they may relate to the neurobiological reactivity to and recovery from a subsequent acute laboratory-induced psychosocial stressor. We further aim to manipulate the elapsed time between the exercise bout and psychosocial stressor to examine whether elapsed time impacts the magnitude of the cross-stressor adaptation. Finally, we will test if there are differences at the intersection of sex, age, or cardiorespiratory fitness. This Discovery Grant will allow me to implement a program of research that will identify fundamental mechanisms associated with cross-stressor adaptation, opening the door to future investigations that test whether repeated bouts of exercise lead to reduced responses to psychosocial stressors, as evidenced in previous quasi-experimental studies. This research will deepen our knowledge of fundamental mechanisms relevant to human life sciences and behavioural neuroscience.