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