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physical exercise intervention (O’Dougherty et al. 2012 ). The STAI has been


shown to be significantly correlated with the Perceived Stress Scale (e.g., Turner


et al. 2013 ; Wongpakaran and Wongpakaran 2010 ) in several studies.


Biological Responses to Stress


Initial biological responses to stress, based on activation of either the


sympathetic-adrenal medullary or pituitary-adrenal cortical systems, long predate


Homo sapiensand serve as biological markers of stress independent of reporting bias.


This two part biological response in the alarm reaction differs slightly in time frame,


with the sympathetic-adrenal medullary response activated within seconds (Brunner


and Marmot 1999 ) and the peak pituitary-adrenal cortical response occurring after 10–


30 min (Kudielka and Kirschbaum 2005 ; Pollard and Ice 2007 ; Dickerson and


Kemeny 2004 ). Cognitive areas of the brain send stress messages to other brain areas,


particularly the amygdala and hypothalamus. The amygdala has a primary role in the


stress response (Kim et al. 2001 ), with neurons in this brain area releasing


corticotropin-releasing hormone (CRH) that causes the hypothalamus to stimulate the


sympathetic nervous system. This leads to the release of norepinephrine by sympa-
thetic nerves, and epinephrine by the adrenal medulla (Brown 2007 ).


The two pronged stress response leads to a host of physiological changes in the


body, as shown in Fig.7.2. In short, the sympathetic-adrenal medullary response


leads to a temporary decrease in pain sensitivity, an increase in heart rate and stroke


volume, elevated blood pressure, an increase in pulmonary ventilation along with


dilation of lung bronchioles, and stimulation of glucose release from the liver


through glycogenolysis. Bloodflow is also preferentially diverted to muscles and


brain from other areas, such as the gastrointestinal tract. This comprises the“fight or


flight”response, in which blood is sent in greater quantities to muscles while loaded


with oxygen and fuel to permit vigorous muscular activity—whetherfighting or


fleeing from perceived danger.


A few minutes later, the hypothalamus releases CRH that stimulates the pituitary


gland to release adrenocorticotropic hormone (ACTH). ACTH, in turn, causes the


adrenal cortex to release steroid hormones—primarily cortisol in humans. Cortisol


in turn has multiple physiological effects such as: control of blood glucose levels


through both gluconeogenesis and synthesis of glycogen in the liver (Beck and


McGarry 1962 ; Khani and Tayek 2001 ; Kyrou and Tsigos 2009 ), control of


electrolyte levels, downregulation of immune responses through inhibition of T-cell


proliferation, and temporary reduction in histamine secretion, thus reducing


inflammation (Charmandari et al. 2005 ). Cortisol feeds back to the hypothalamus,


leading to reduced secretion of CRH. Stress hormones also have other neurological


effects, including enhanced learning and memory as well as heightened feelings of


anxiety and fear (Cahill and McGaugh 1998 ).


The physiological response to stress provides many different biological markers
of stress during people’s normal activities. There are some constraints, however.


7 Stress Biomarkers as an Objective Window on Experience 121

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