Abstract

Stress refers to the consequences of the failure of a human or animal to respond appropriately to emotional or physical threats to the organism, whether actual or imagined (Seyle, 1965), resulting in disruption of homeostasis. In particular, the causes or consequences of stress in modern-day life include interpersonal, social, familial, societal, and social psychological factors. Evidence from population cohort studies suggests that psychosocial stress is a risk factor for cardiovascular diseases (CVD) (Kivimaki et al., 2012; Brotman, Golden, & Wittstein, 2007; Rosengren et al., 2004). An important way of investigating the mechanisms underlying these associations is acute psychophysiological stress testing, involving measurement of cardiovascular and biological responses to laboratory-induced behavioural stressors (Steptoe, 2007). Psychophysiological stress testing allows individual differences in responses to standardised stress tasks to be evaluated and related to psychosocial factors (Chida & Hamer, 2008) and future risk of CVD (Chida & Steptoe, 2010). Behaviourally evoked psychophysiological responses are relatively stable individual characteristics, consistent across time and stressor type. The magnitude or pattern of an individual's stress response is largely mediated by the immediate actions of the autonomic nervous system and delayed response of the hypothalamic pituitary adrenal (HPA) axis, which releases various hormones (i.e., catecholamines, cortisol, etc.) into the circulation. These systems drive specific responses that include an increase in blood pressure (BP) and heart rate, changes in cardiac sympatho-vagal balance, skeletal muscle vasodilatation, the stimulation of haemostatic and inflammatory responses, and activation of various immune cells, all of which might be relevant to CVD risk. Individual differences in patterns of stress responding are accounted for by factors such as race and ethnicity, genetics, background stress, and lifestyle habits. In particular, exercise has been studied for its stress buffering effects. Physical exercise and mental stress have similar acute physiological effects in that both result in cardiovascular activation and release of catecholamines and cortisol, although paradoxically they have different chronic effects on health – regular exercise is associated with protective effects whilst chronic mental stress has been linked with health risks, in particular CVD. This paradox is poorly understood, and might prevent some health professionals from acknowledging the true importance of physical activity in treating stressrelated illnesses. The goal of this chapter is to focus on the effects of exercise on psychophysiological stress responses, with reference to pathophysiological mechanisms in health and disease.