Occupational Stress and Burnout

Abstract

The concept of stress can be considered so multifaceted that one single process or definition does not explain the whole phenomenon. Physical or psychological demands, known as stressors, can cause strain. Stress can be identified as the process in the body for adapting to influences, changes, demands, and strains to which it is exposed. Stress caused by a working environment is known as occupational stress and globally considered to be among the topmost serious health issues. Stress and burnout have reached all-time highs across various professions as stressors have become assiduous and indeterminate - employers and employees alike are scrambling to return to normalcy in the working environment. Burnout results from the physical, mental, and psychological reactions from experiencing prolonged stress. Burnout, considered an occupational phenomenon rather than a medical condition, is often exacerbated with depression and anxiety leading to concerns of employee well-being and mental health. The progressive escalation of occupational stress and burnout has gained attention from global organizations and as the nature of work continues to evolve, understanding occupational stress can support initiatives for managing it.

1. Introduction

• Explore the concepts of stress and strain.

• Explain occupational stress.

• Explicate causes of occupational stress.

• Examine how occupational stress can lead to burnout.

As so cleverly denoted by Selye, the founder of the term ‘stress’ as we know it today, “Everybody knows what stress is and nobody knows what it is…Stress in health and disease is medically, sociologically, and philosophically the most meaningful subject for humanity that I can think of.” [1].

2. Background

The terms “strain” and “stress” were introduced into the health psychology language in the 1920s whereby strain suggested structural changes and stress emphasized external factors. Cannon [2] defined stress as physical and psychological “disturbances” that threaten homeostasis (the body’s state of balance). These disturbances were termed as a “fight or flight” expression and used to describe the physiological changes that occur to mobilize energy to the body to fight or flee when threatened by a stressor. The ‘fight or flight’ reaction activates the sympathetic nervous system – targeted muscles increase heart rate, blood pressure, and respiration, decrease digestion, increase perspiration to cool the body, and pupils dilate [3]. Selye’s experiments in the 1930s and 1940s discovered that a variety of aversive stimuli produced these physiological responses and coined this response “stress”.

Selye identified the general adaptation syndrome (GAS) as the set of responses to diverse types of stressors [3, 4]. Research by Holmes and Rahe [5] concluded that an accumulation of life events was found to be harmful to health. Cassel [6] introduced the vulnerability or resistance of the individual who was exposed to stressful stimuli into the theoretical framework as a factor in the outcome of stress and the effect of stress on health.

Various definitions of stress emerged; however, a common and acceptable definition is still lacking because the concept has not only become so widespread, but the term is also used so diversely by so many people in so many different situations and settings. The concept or term can be considered so multifaceted that one single process or definition does not explain the whole phenomenon. Stress definitions are generally categorized in three ways: (1) Stress as a stimulus, (2) Stress as a response, and (3) Stress as an interaction between an organism and its environment [7].

Selye’s triadic model can be used as a basis for the stress-response pattern. When experiencing stress-induced physiological changes, the following stages may occur – each associated with changes in nervous and endocrine functioning: alarm, resistance, and exhaustion [8, 9].

• Alarm – When encountering an acute stressor, the amygdala sends signals to the hypothalamus (functions as the brain’s command center) which activates the sympathetic nervous system and adrenal glands release the hormone epinephrine into the bloodstream. This process can elicit physiological changes (rapid heartbeat, fast breathing, surge in energy, etc.) and is otherwise known as the fight, flight, or freeze response [10].

• Resistance – Once the stress has passed, the parasympathetic nervous system minimizes the body’s stress response. If the stressors continue, stress hormones will continue to produce additional symptoms such as irritability, frustration, or poor concentration [10].

• Exhaustion – Prolonged and chronic stress can cause the stress response to repeat in the body which may lead to anxiety, fatigue, depression, burnout, sleep disturbances, heart disease, psychiatric disorders, etc. [10].

The complex construct of stress initiated other various models and theories to describe the process. Most recognized theories originated from Kagan and Levi’s stress-disease model [11], Levi [12], Lazarus and Folkman’s transactional theory of stress and coping [13], and Seyle’s general adaptation syndrome [14]. Although Selye was noted as the pioneer of stress response theory, other contributors in the field of stress response included Mason [15], McEwen and Mendelson [16], and McEwen [17].

As one of the most interesting and mysterious processes, the study of stress not only focuses on what happens in the body during a stressful experience but also on what occurs in the psyche of the individual mind. Current psychological theories of stress evolved from the Theory of Emotion (James-Lange) [18, 19], The Emergency Theory (Cannon-Bard) [20, 21], and the Two-Factor Theory of Emotion (Schachter-Singer) [22].

3. Stress, stressors, and strain

Stressor: Stimuli from the environment that causes a state of strain or tension – forcing adaptation or change.

Experienced Stress: Challenged with more demands than perceivably able to manage (based on personal physiological and psychological perception).

Strain: Force that causes a change in the body when stress is present (Figure 1).

Figure 1.

Stress process model.

Stress can be identified as the process in the body for adapting to influences, changes, demands, and strains to which it is exposed. The National Institute of Mental Health defined stress as the physical or mental response to an external cause. This response can be either positive, referred to as eustress, or negative, referred to as distress [8]. Stress responses allow for adaptation and adjustments to new situations. Positive response may be focus and alertness from the production of adrenaline, triggered by stress and the body’s ‘fight or flight’ response. We all have some level of stress in the body and therefore the body has a stress response; however, at times of great distress, the stressors experienced may be too excessive with an inability to cope and thus cause strain. Stress can be viewed positively or negatively depending on the situation and severity of the experience. If we view an exhausted athlete who won the gold medal or a newly promoted stressed-out business executive, we may view this experience as positive. Both individuals may have achieved exceptional goals towards accomplishment; however, the strain may have caused stress in the body. Consider the commitment to training or working long hours, even possibly disrupting a healthy work-life balance. Negative results could be physiological such as harm to muscles, elevated blood pressure, disrupted sleep, or other developed heart conditions. Whereas positive responses to stress could be alertness or motivation, negative responses emerge when stress from continued stressors without relief continues.

Physical or psychological demands, known as stressors, can cause strain. Continued strain from stressors can cause individual adaptive capabilities to be overextended and lead to chronic behavioral, emotional, psychological, physiological problematic outcomes [23, 24]. Stress is a state of mental, emotional, or physical “strain” or tension resulting from opposing or very demanding circumstances. One can experience stress without strain, but strain requires the presence of stress. Strain results from stressors, pulling or pushing an individual in different directions. Unmanaged and overwhelming stress with an inability to adapt to the proper context or situation can cause negative outcomes and the response could be anxiety, depression, insomnia, fatigue, procrastination, elevated heart rate, or even high blood pressure. Fundamentally, “strain” causes “stress.”

4. Stress response

Intrinsic and extrinsic adverse factors (known as stressors) that threaten homeostasis trigger the stress response. To counteract, maintain, or restore homeostasis (body equilibrium or eustasis), physiological and behavioral responses are activated as the adaptive stress response. Activation is required from a complex range of responses in the body, including the endocrine, nervous, and immune systems to maintain homeostasis during times of chronic stressors – collectively known as the stress response and crucial for stress management [25]. These responses are highly dependent on intricate and interconnected cellular, molecular, and neuroendocrine infrastructure to create the stress system.

Neurohormone systems regulate the maintenance of homeostasis and allostasis (otherwise known as defective homeostasis, dyshomeostasis, or distress) during stress. The hypothalamic-pituitary-adrenal axis, or HPA axis, identifies the interaction between the hypothalamus, pituitary gland, and adrenal glands which play a prominent role in the body’s response to stress. The hypothalamus manages many functions in the body such as releasing hormones and conserving the body’s internal balance. The pituitary gland signals other glands to release hormones [26, 27]. The adrenal glands function in producing hormones for regulation – including metabolism, immune system, blood pressure, stress response, and others. The cortex of the adrenal glands produces corticosteroids and this pathway of the axis results in the production of cortisol, providing energy for the body to manage the stressor. The hypothalamus releases Corticotrophin Releasing Factor (CRF), transported by the bloodstream to the pituitary gland, then produces Adrenocorticotrophic hormone (ACTH) when chronic stressors are perceived [28].

The initial stress response is mediated by the sympathetic nervous system and occurs almost immediately, releasing the secretion of epinephrine and norepinephrine hormones. These hormones strive to maintain homeostasis during times of stress by binding to the cells they target to relay messages and activate changes to the body (e.g., metabolic changes, release of glucose, increase of blood flow, etc.). After the initial response, the HPA axis will be stimulated, and the hypothalamus will release corticotropin-releasing hormone (CRH) – the central regulator of the HPA axis [27].

The Sympathetic-adrenal-medullary (SAM) system and Hypothalamic-pituitary-adrenal (HPA) axis work concurrently, activating the energy needed to respond to stressors.

• Sympathetic-adrenal-medullary (SAM system) response – Responsible for the release of hormones (epinephrine and norepinephrine by the adrenal gland) that redirect energy within the body to muscles that help us respond to stressors. Referred to as the “fight or flight” response (increases in heart rate, blood pressure, and respiration; decrease digestion; and dilate pupils) [29].

• Hypothalamic-pituitary-adrenal (HPA) axis response – The main stress response system responsible for maintaining body homeostasis (balance). The hypothalamus secretes corticotropin releasing hormone (CRH) signaling the pituitary gland to release adrenocorticotropic hormone (ACTH) and initiating the adrenal glands to release cortisol and glucocorticoids (stress hormones) [29].

5. Person-environment fit theory

The term person–environment fit was devised by French and colleagues in 1974 [30] and corroborates Lewin’s [31] belief that behavior is a function of a person and the environment which corresponds to the “whole is other than the sum of its parts” in Gestalt psychology.

Kurt Lewin’s behavior equation

$${\text{Lewin}}^{’}\text{s}\text{Heuristic Formula}:B=f\left(P\text{,}E\right)$$E1

Behavior = B; f = function of Variables: Person = P; Environment = E

The theoretical perspective of person–environment (PE) fit contributes to interactional psychology – the primary driver of human behavior is the interaction between personal and environmental attributes. The PE fit ideology crosses two lines of scholarship – environmental perspective and person-centered perspective. Organizational environments are recognized as being one of the most important settings with which people may fit or misfit within the PE fit research. The overarching theme surrounding this theory is that certain individuals or persons are better matched for certain environments than others.

Stress results when there is a bad “person-environment” fit. This bad fit or misfit can be objective, subjective, or both. In other words, the environmental demands are not matched (or fit) to individual ability. In the context of work, an example would be a worker having the ability to perform work, but if additional work or duties are required beyond the ability of the worker, the fit becomes bad. The paradoxical mystery of the amount of stress that equates to a “misfit” is not fully known because everyone is unique and has varying degrees of responses. Nevertheless, individual motivation, behavior, and health (mental and physical) can be affected by the compatibility between a person and an environment. A compatible match could equate to aided functioning within an organization whereas an incompatible match could equate to instability creating tension on both the P side (exhibiting as job stress, dissatisfaction) and tension on the E side (exhibiting as absenteeism, reduced performance) of the PE fit eq. [32].

6. Occupational stress

Stress caused by a working environment is known as occupational stress and globally considered to be among the topmost serious health issues. Occupational stress can be described as a mental and physical condition that can create negative organizational and individual outcomes [24, 33, 34, 35, 36, 37, 38, 39]. The World Health Organization (WHO) defined occupational stress as “the response people may have when presented with work demands and pressures that are not matched to their knowledge and abilities and which challenge their ability to cope” [40]. Furthermore, WHO declared occupational stress as a global occupational phenomenon and an epidemic because of the negative economic, health, and social outcomes [23, 24, 40]. Similarly, the National Institute for Occupational Safety and Health (NIOSH) defined occupational stress as “the harmful physical and emotional responses that occur when the requirements of the job do not match the capabilities, resources, or needs of the worker.” [24, 41].

You could be experiencing workplace or occupational stress if your job demands more than you can deliver or perform [42]. The inability to avoid tensions in the workplace can be psychologically overwhelming when experiencing too much stress [43]. With any employer, at some point, the pressure of work-related stress is common to most employees. As employers and employees alike are scrambling to return to normalcy after the pandemic in the working environment, change can create stress and anxiety. The scientific community internationally was compelled to find answers and therapies to control SARS-CoV-2. In 2020, WHO [44] affirmed a public health emergency (PHE) of international concern, the highest level of alarm under international law. Heightened rates of burnout were experienced throughout the country by 2021 [45] and continued until the Public Health Service Act (Section 319) expired in May of 2023 by the Department of Health and Human Services (HHS) [24, 46]. This traumatic experience and change in normalcy intensified occupational stress among employees globally.

For most people, a quarter to a third of their lives are spent in the workplace. For that reason, maintaining a healthy work-life balance is essential for mental and physical health. According to Mental Health America [47], four in five employees report that workplace stress affects their relationships with friends, family, and coworkers. With Americans struggling with so many external stressors out of their control, over 25% reported that they are so stressed they cannot function on most days [48, 49]. Gallup’s State of the Global Workplace report found that U.S. workers reported the experienced stress level to be 20% higher than the global average [50].

Based on the statistics found in the NIOSH report, 40% of workers described their job was very or extremely stressful; 25% of workers considered their jobs as the number one stressor in their lives; 29% of workers reported quite a bit or extremely stressed at work; and 26% of workers identified often or very often burned out or stressed by their work [41]. Approximately 3 in 5 employees reported negative effects of work-related stress, such as lack of interest, motivation, or energy (26%) and lack of effort at work (19%). In addition, 36% of employees expressed cognitive weariness, 32% portrayed emotional exhaustion, and 44% experienced physical fatigue [45, 48]. Roughly 65% of U.S. workers surveyed (each year consistently) have considered work as being a very significant or somewhat significant source of stress [50, 51]. According to WHO, 83% of US workers suffer from work-related stress and 54% of workers report that workplace stress affects their home life [52].

Occupational stress research has been explained through other various models such as the Job Demand-Control-Support model, the Effort-Reward Imbalance model, and the Job Demands-Resources model [53, 54, 55, 56, 57]. Although many challenges emerged in stress literature historically, five significant organizational factors have been correlated as sources of occupational stress within the content and context of work environments: (1) Intrinsic workplace factors, (2) Role factors, (3) Career development factors, (4) Relationship factors, and (5) Organizational structure, formalization, and culture factors [33, 34, 36, 48, 58, 59].

Intrinsic workplace factors originate from the content of work, creating a mismatch between demands and individual capabilities (i.e., person and environment) to cope with such demands [60]. Examples of these intrinsic factors could be workload (overload or underload), time pressures or demands, poor physical work conditions, lack of job meaningfulness, or other similar problems. Role factors could include any unclear work or conflicting roles or boundaries causing stress including role ambiguity, role conflict, or level of responsibility. Career development factors might include job instability or insecurity, lack of training, stagnation, or even under/over promotion. Relationship factors may include poor relationships with colleagues or managers/leaders, discrimination, or even bullying. Organizational structure, formalization, and culture factors could include office politics, decision-making participation, or leadership [33, 34, 36, 48, 58, 59]. Work stressors associated with producing strains resulted in increased tension including (a) diminished job-related attitudes (job satisfaction, intentions to leave or quit, organizational and work-unit commitment), (b) lower levels of psychological health, and (c) burnout (causing emotional exhaustion, depersonalization, and a diminished personal accomplishment) [34, 48, 61].

With reported increases in occupational stress throughout the country, research attention has shifted to psychosocial risk factors from chronic exposure to stressors in occupational settings and the adverse effects of stress on chronic disease [62, 63, 64]. Psychological and psychosocial well-being is not only important to employee productivity and work satisfaction but also the onset of mental health and physical health [65, 66].

7. Examples of stress by workers in various industries

When we think of stressful jobs, we may think about Soldiers defending our country or firefighters who brave flames for our safety. Enlisted military service members were highlighted as having the most stressful job in the world [67]. Among the other top four most stressful occupations were firefighter, airline pilot, and police officer [68]. According to the American Institute of Stress, 62% of employees have elevated levels of stress, with extreme fatigue/feeling out of control with causes of stress reported as workload, people issues, work-life balance, and lack of job security [51].

Although there is associated stress with almost all jobs, some have more than others. The Occupational Information Network (O*NET), part of the U.S. Department of Labor, ranked 873 of the most stressful jobs, requiring the ability to accept criticism professionally and react calmly and effectively in high-stress situations. Interestingly, not all careers listed as stressful included high salaries. Jobs noted among the top twenty stressful jobs included: lawyer, judge, physician, surgeon, nurse, operator, sales manager, structural iron/steelworker, security guard/officer, financial analyst, compliance officer, and therapist/counselor [69, 70].

8. Stress disorder and burnout

Stress can be measured subjectively or objectively. If we consider stress caused by external events (stressors) that increase demands or change, stress may be measured objectively by those stressful events. However, if stress is measured by self-reporting or by an individual’s perception of stress caused by stressors, the focus shifts to a subjective measure. Therefore individual experiences, perceptions, and coping strategies may differ. Whereas one individual may successfully manage distress to reduce associated negative health, mental health, and behavioral outcomes, another individual may experience clinically significant distress or impairment in the forms of acute stress disorder, post-traumatic stress disorder (PTSD), or secondary traumatic stress (also known as vicarious traumatization) [24].

Acute stress disorder can develop following a person’s exposure to one or more traumatic events [24, 71]. The Association for Behavioral and Cognitive Therapies defined PTSD as a stress-related disorder that develops after a traumatic experience, involving a combination of emotional, physical, and behavioral symptoms because of experiencing the traumatic event and that significantly affects the daily well-being of a person [24, 72]. The Vicarious Trauma Institute defined vicarious trauma as an indirect exposure to trauma through a first-hand account or narrative of a traumatic event [73]. Or in like terms, the trauma that can occur after exposure to someone else’s trauma [74].

Stress can illicit extreme pressure and burnout results from the physical, mental, and psychological reactions from experiencing that prolonged stress. In 1974 Freudenberger described the term “burnout” as “the extinction of motivation or incentive, especially where one’s devotion to a cause or relationship fails to produce the desired results.” [75]. Burnout syndrome (BOS) has historically been attributed to caring or helping professions, in which the term referred to a particular experience and mental state in the workplace prior to evolving into a psychologically and clinically relevant condition. Now the terms burnout and BOS are associated with almost every industry [76]. In the tenth revision of its International Classification of Diseases (IDC-10), WHO called it “a state of vital exhaustion” [77, 78]. Workplace burnout is an occupation-related syndrome resulting from chronic stress that has not been successfully managed [43, 79]. Symptoms of burnout can contribute to other physical and mental health problems, such as insomnia, reduced cognitive function, blood disorders, and coronary heart disease according to the American Psychological Association and The American Institute of Stress [45, 50].

Burnout and stress are at all-time highs across professions. WHO declared burnout an occupational phenomenon – rather than a medical condition – in the eleventh revision of its International Classification of Diseases (IDC-11) [80]. Characterized by feelings of exhaustion, disengagement from one’s job, increased mental distance with feelings of negativism or cynicism related to one’s job, and a sense of diminished professional fulfillment or efficacy – burnout is considered the result of chronic work stress that the individual is not able to manage [24, 81].

Prolonged stress can cause acute and chronic changes in the body. Common, or regular stress can be managed through adaptation. However, chronic, and pathological stress may result in negative physical and mental health outcomes. Specifically, two distinct adverse outcomes of stress are burnout and depression [82, 83, 84]. Burnout has long been understood as an outcome of prolonged, unresolvable, work-related stress [85, 86, 87]. Burnout encompasses three responses to chronic job-related stress: (1) decreased energy or emotional exhaustion, (2) depersonalization or cynicism, and (3) diminished personal accomplishment, lower productivity, or professional inefficacy [80].

Burnout and depression have been reported as two key indicators in occupational or workplace distress research. Depression manifests in affective, behavioral, cognitive, and somatic symptoms including dysphoric mood and anhedonia. However, depression can be considered as a “dimensional phenomenon – a continuum – with only individuals at the highest end of the continuum meeting criteria for formal diagnoses of depression.” [88]. Symptoms of depression are outlined in the Diagnostic and Statistical Manual of Mental Disorders according to the American Psychiatric Association. Clinically significant distress or diminishment in areas of functioning (e.g., social, occupational, etc.) must be caused to receive a diagnosis of depression [89]. Consequently however, there are no clear diagnostic criteria for burnout. Even so, burnout and depression can complement one another. In other words, an individual may have increased symptoms of depression with increased symptoms of burnout [88].

With a profoundly shifting employment landscape, escalating employee mental health challenges, and the steadfast risk of an economic recession, burnout in employees climbed as a critical concern for employers. Based on the American Psychological Association 2023 work survey, a combined 92% of employees said it is very or somewhat important to work for an organization that values their emotional and psychological well-being and that provides support for employee mental health [90].

Burnout is a substantial issue that has beleaguered employees over the past few years – exacerbated by the pandemic and its mass problems, including blurred lines between work and home life as remote work became the norm. Burnout can cause both individual and organizational consequences. Individual effects of burnout can present as decreased productivity, substance abuse, intensified anxiety and/or depression, or other health issues. Organizational effects of burnout can be contributed to depressed commitment, increased absenteeism and presenteeism, and greater employee turnover. It is reported that employees who experience workplace burnout have a 57% increased risk of workplace absence greater than 2 weeks due to illness; 180% increased risk of developing depressive disorders; 84% increased risk of Type 2 diabetes; and 40% increased risk of hypertension. Additionally, workplace burnout is associated with cognitive impairment across multiple cognitive domains: short-term memory, attention, and other cognitive processes essential for daily work activities [43, 91].

According to the State of the Global Workplace report, 85% of employees are not engaged or are actively disengaged at work [92]. This sign of global mismanagement [93] results in struggling organizations and frustrated employees – prompting a burnt-out work culture to grow exponentially. The “Great Resignation” or “Great Disengagement” is evident throughout industries and burnout has been cited as a leading cause. The pandemic blurred the lines between work and home for many employees and workers strove to establish boundaries in their work-life balance [24].

9. Quiet quitting

Quiet quitting is often used to cope with burnout and nearly 6 in 10 employees are doing so. Differences in definitions emerged for quiet quitting. Whereas some define quiet quitting as not actively going above and beyond at work, others argue it is a form of passive resistance to redraw the boundaries between employees’ professional and personal lives. In general terms, quiet quitting describes a trend where unmotivated, disinterested, and checked-out employees do bare-minimum work at best [94]. Quiet quitting can result when an organizational culture fails to deliver on employment promises tarnishing employee trust and employees psychologically disengaging from work. Employees want more engagement with a positive culture promoting recognition, opportunities to gain experience and learn, fair treatment, clearer goals, and better managers. Employees also want pay with benefits and effective well-being [95].

10. Loud quitting

Another trend to cope with occupational stress is loud quitting. Whereas quiet quitting can be referred to as employees that are not engaged, loud quitting refers to employees that are actively disengaged. Loud quitting occurs when employees not only feel unhappy at work but resentful that their needs are not being met by the employer and act out on that unhappiness as a result. Loud quitters often report more stress – compared to other employees – and are much more likely to be actively looking for a different job [96]. The combination of loud quitting and quiet quitting employees cost the global economy $8.8 trillion. Nearly 1 in 5 workers are ‘loud quitting’ and this occupational phenomenon is more extreme than ‘quiet quitting’. Based on the State of the Global Workplace Report, 18% of employees admit to loud quitting and 59% say they are quiet quitting [95, 96, 97].

11. Conclusions

With the progressive escalation of occupational stress, attention from global organizations has increased – American Psychological Association (APA), Centers for Disease Control and Prevention (CDC), Mental Health America (MHA), National Institute for Occupational Safety and Health (NIOSH), Society for Occupational Health Psychology (SOHP), World Health Organization (WHO), etc. Paradoxically, mental health awareness has found a voice not only in the public through media exposure and workplace policy, but increased stress has exacerbated burnout and exhaustion.

The study of occupational stress has evolved and proves to be a difficult endeavor because of the complex nature of the topic. Numerous factors can influence the development and exacerbation of workplace stress. In addition, workplace stress is highly subjective and objective in terms of exposure, outcomes, and coping mechanisms. While individual differences and perceptions are critical to note, scientific evidence correlates certain working conditions stressful to most employees such as psychological well-being, commitment from the organization to the employee, and resources [65]. As the nature of work continues to change at whirlwind speeds, occupational stress will continue to pose a threat to the health of employees and employers. Therefore, understanding occupational stress can support organizational change by implementing effective occupational stress prevention, coping skills, and interventions.

Definitions of key terms

Stress: a state of worry or mental tension caused by a challenging or threatening situation [52].

Stressor: experiences that cause stress or strain and threaten homeostasis.

Acute stress: any stress that is experienced for a brief time.

Chronic stress: any stress that is experienced for a long time.

• Stress response: physiological and psychological changes that occur as a reaction to the stressors experienced (also referred to as stress).

• Fight or flight response: activation of the sympathetic nervous system to prepare the body to fight or flee in response to a perceived threat [3].