Some Notes on Stress
(Note: for references cited on this page, see the Reading List)
1) Concepts and Definitions of Stress
There is an intuitive and familiar sense of "stress" that anyone can explain. Beyond this popular conception, however, there is wide disagreement over a more exact definition and over how it should be measured.
Before stress was used in a scientific context it meant hardship, adversity or affliction.
Osler's writings on angina in the early 20th century equated stress with hard work, and strain with worry.
Adolf Meyer (1866 - 1950) studied the role of stressful events in causing physical and psychological disorders. This later led to the study of "life events" - sudden changes that may trigger sickness.
Research after Meyer has identified a consistent relationship between a variety of stressful events and physical and psychological disorders. The general view is that such events create a temporary state of disequilibrium, which requires adjustments aimed at establishing a new homeostasis. The extra effort required in the adaptation process is viewed as potentially draining, and thus contributes to the deterioration of one's general well-being (Cronkite & Moos, p. 373). Correspondingly, ‘healthiness’ may refer (as in the WHO 1986 conception) to the ability to cope with and change one's enviornment: resiliency.
Hinkle added the theme of diseases of adaptation: "It is now generally agreed that diseases may be as much the result of the adaptive reactions of the host as they are of the damaging effects of pathogenic agents, and it is widely accepted that the relation of people to the other people around them and to the society in which they live are important causes of disease." (Hinkle, 1973:31). This may remind us of inflammatroy processes: is the stress response "a common, natural and innate response to injury"?
Research into the link between stress and disease is heuristic, not phenomenal. It is different from isolating a particular enzyme and studying its effect – stress is not an objective phenomenon that we can study under various circumstances and interpret, but it is a useful heuristic concept that shows connections between what would otherwise appear to be quite disparate conditions.
Hence, Lazarus suggested that stress should be looked upon as a rubric (rather like motivation, or cognition), rather than as a simple variable. The research task is to select from among alternative concepts of stress that which offers the most explanatory power, and then to find ways to measure it in empirical studies.
The following sections sketch some of the alternative conceptual approaches to stress with their advantages and weaknesses. Most theories begin as oversimplifications that are replaced with more complex approaches as needed. We should prefer the simple, as long as it is also adequate.
2) Stimulus Models & Life Events
Applying the engineering approach, stimulus-based definitions view stress as an independent variable that disturbs the individual: stress leads to distress. This approach stimulated a research tradition that concentrated on stressful stimuli, classifying them in terms of the demands they place on individuals. Hence the life events research tradition that led to measurements such as the life change units score of the "Schedule of Recent Events." This is a simple Stimulus–Response reaction in which an antecedent event leads to long-range adaptational outcomes. It follows a behaviorist tradition, with "the assumption that experiences in life may cause illness. Stress, then, consists of those experiences. They may act singly or cumulatively, but if they are intense or frequent enough, the individual is likely to fall "sick" (Martin, 1984:450).
In the stimuluis conception of stress, the appraisal or coping processes whereby people manage stressful events are not often studied. Where they are, the research paradigm still retains the view that life events are the stressors, and things like personality modify the link between input and outcome. But more sophisticated versions of the model do posit that people have an elastic limit, beyond which resistance to stress is reduced, leading to psychological or physical damage (see Selye's "exhaustion" theme).
Criticism of the stimulus approach came from several directions. Analogies were drawn with the move away from viewing pathogens such as viruses or bacteria in strictly mechanical terms, as these do not act in the same manner on all people exposed to them. Mason, in 1975, wrote:
There is a complex assemblage of intervening "host resistance" machinery which has a major role in determining whether infection will progress into illness or not. In principle, this intervening "host resistance" machinery would seem to be generally analogous to the intervening psychological impact of psychosocial forces upon the organism, although the latter machinery does differ considerably in the greater degree of its complexity (p.33) (Mason JW. A historical view of the stress field. J Hum Stress 1975;1:22-36).
Thus the stimulus approach does not attempt to explain the wide variability in human responses to ostensibly the same stressor. Nor does it handle the problem of underload or under-stimulation. Furthermore, treating stimuli in a mechanical manner is further shown to be insufficient by the studies that point to the importance of the meaning of the event, beyond the event itself. For example, hearing a phone ring may produce a wide variety of emotional responses, according to one's expectations: if you are waiting for a call from the airport that your spouse has returned, versus if you are anticipating a call to return to the hospital to be with your dying father.
As Selye charmingly admitted, the term is also used incorrectly: in physics, there is no negative connotation and stress merely refers to the force applied to a body. Strain refers to the resulting deflection in the body: stimulus and response.
This leads to Young's modulus which shows the stiffness of a material. It graphs strain (amount of bending) for various levels of stress; different curves characterize different materials (some, like glass, are brittle and break abruptly without deflecting, while others like spring steel can bend greatly before breaking). Note that the strain response may not be linear: when you blow up a balloon, it takes a hard blow to get it started, then as the balloon starts to inflate, less puff is required, until it is almost full, when you have to blow harder (and with rising apprehension).
Could we, perhaps, apply some of these ideas to thinking about people: do different people (like different materials) exhibit different strain curves as stress is increased? Are some people "brittle" and others more flexible, laid back or resilient? How would you measure this?
The next phase of stress research focussed on the processes that transform the antecedent variables into responses, and shifted attention from the causal antecedents towards mediating variables.
3) Response Definitions
Considering stress as a response led to some of the confusion in terms: originally the term "response to stressors" was used, to be shortened to the more convenient "stress response." It was then an easy step to further shorten this to "stress," thereby effectively moving stress to refer to the response rather than the stimulus. There is then a logical circularity in explaining a person's response to stressors, which are usually defined as anything that elicits a response. There is a tautology if stress is defined as a response to something that is stressful.
Hans Selye (1907 - 1982). Selye's work has had a profound effect on this field, and many of his conclusions agree with those of Wolff's earlier work. Both agreed that stress should not be viewed in a purely physical sense (e.g. dynes per square centimeter); stress was not used to refer to direct exchanges of energy, as in a fall that leads to a hip fracture. Both Selye and Wolff agreed that the relation between the strength of the input and the subsequent response is not linear; both held that stress should be viewed not as a direct cause, but as a trigger for the organism's response, mediated via the CNS.
Selye's contributions to the concept of stress included his emphasis on the notion that, while each input may have a unique effect, they nonetheless all produce a consistent core set of responses. This he termed the "nonspecific" stress response, as it is the same whether the stimulus is pleasant or unpleasant; the nonspecific response varies in intensity but not in kind. (This might be offered as a justification for the inclusion of both positive and negative events in Holmes and Rahe's adaptation scale). Selye also emphasized that stresses cannot, even should not, be avoided: he distinguished between beneficial stress ("eustress") and harmful. Illness results when the body can no longer adapt to the stressful inputs, producing diseases of breakdown in adaptation. As with Young's modulus, this does not occur in a linear fashion, nor are the thresholds for falling sick consistent across different individuals. Here, Selye spoke of adaptation energy, a hypothetical construct used to explain why not all people react to stresses in the same manner. Selye's major contribution was in setting out the physiological form of the stress response; details of this are of less interest to us in the present course on social epidemiology. (Selye H. The stress of life. New York: McGraw Hill, 1956)
Picture of Selye; Summary of his work.
Harold G. Wolff (1898-1962). In 1953, Harold Wolff published "Stress and Disease", an early book on psychosomatics. He did not fully define stress, seeing it as "man's response to many sorts of noxious agents and threats." The term "response" suggests something active, and should not be equated with passive strain. "I have used the word [stress] in biology to indicate that state within a living creature which results from the interaction of the organism with noxious stimuli or circumstances, i.e., it is a dynamic state within the organism; it is not a stimulus, assault, load, symbol, burden, or any aspect of environment, internal, external, social or otherwise."
Wolff pointed the way out of a mechanistic interpretation of stress in causing disease. He distinguished between unconditional stresses, which cause direct damage (fracturing a bone), and conditional stresses whose effect is indirect, and only cause harm because of some prior event. These even include symbols that may have deep meaning for the individual, according to past experience (a swastika, for example). The impact of a life event may not be attributed to the event per se, but to the meaning it had for the person; the same experience can have widely different effects, depending on a person's expectations and coping abilities.
Later, Wolff modified his views, reducing the centrality of stress in his thinking: "The resemblance of stress to the situation in living systems is remote, yet, figuratively the concept is useful, and when employed in reference to human problems merely implies an analogy to the order in non-living systems. Since stress is a dynamic state within an organism in response to a demand for adaptation, and since life itself entails constant adaptation, living creatures are continually in a state of more or less stress."
Martin Seligman (b. 1942). Seligman's studies on rats further contributed to freeing stress literature from a mechanistic view of stress as a stimulus - response process. "Exposing animals to inescapable, uncontrollable electric shocks seriously impairs the avoidance or escape behaviours of the same animals when they are re-exposed in an environment in which the shocks are controllable by the animal. It seemed to be the animal's perception of the event that makes it stressful". Seligman here uses "perception" to refer to recognition and interpretation of stimuli based on the animal's memory. Recall, also, the work on "executive monkeys."
Executive Monkeys. In 1958, J.V. Brady published a widely quoted study that reported the health effects of receiving electric shocks in monkeys. In particular, he studied the mediating influence of whether or not the monkey could control the shocks. In the experiment, monkeys received randomly timed electric shocks to their feet following an audible signal. Monkeys were in pairs, and the 'executive monkey' in each pair could press a lever to avoid shocks for both of them. The other monkey had no control and received all the shocks that were not prevented by the executive monkey. By the fourth week of undergoing this on multiple occasions each day, the executive monkeys began to die of gastric ulceration. The 'yoked' monkeys, who received shocks but could not act to avoid them, showed little gastric ulceration (see Seligman's theme of Learned Helplessness). This suggested that it was not the shocks themselves that caused the ulceration; the critical factor was the stress associated with being in control of your fate and that of the partner monkey. Subsequent investigators have questioned Brady's findings. For example, it appears that he may have chosen more active monkeys to be the executives, so the effect could have resulted from the personal character of the monkeys. Similar studies on rats have shown conflicting results. This study would now, of course, be considered unethical. (Brady JV. Ulcers in executive monkeys. Scientific American 1958; 199(4): 95-100).
While an advance, there remain problems with the response-based views of stress.
From Selye's ideas of stress as a non-specific response, the approach tends to treat all stressors as equivalent if they produce the same response. Can exercise, drugs, passion and surprise be considered equivalent in terms of their effect on the heart rate? How helpful is this?
Further, emotions and fatigue may be both stress responses and stressors. The commonest criticism of the response theories is that they do not elucidate the perceptual processes that intervene between stimulus and response. It is still a mechanical model that fails to explain different responses in different individuals.
4) Interactional Definitions: Stress and Coping Ability
As may be expected, mid-range definitions have been proposed that combine elements of the stimulus and response approaches. Rather than viewing (from either end) stress as a mechanical process of stimulus or response, the interactional models address the question of why some people are more susceptible than others. Hinkle noted:
"... one cannot simply equate 'hardships', 'straits', and 'difficulties' with a state of health. It appears, rather, that patterns of illness and the frequency of certain kinds of illness change with changing circumstance. In view of the fact that people react to their 'life situations' or social conditions in terms of the meaning of these situations to them, it is difficult to accept the hypothesis that certain kinds of situations are inherently stressful, and certain others are not."
It becomes necessary to think of stress in terms of both the precipitating event, and of the individual's reaction to their ability to cope. Tom Cox (1978) saw stress as
"a perceptual phenomenon arising from a comparison between the demand on the person and his ability to cope. An imbalance in this mechanism, when coping is important, gives rise to the experience of stress, and to the stress response. The latter represents attempts at coping with the source of the stress. Coping is both psychological (involving cognitive and behavioural strategies) and physiological. If normal coping is ineffective, stress is prolonged and abnormal responses may occur. The occurrence of these, and prolonged exposure to stress per se, may give rise to functional and structural damage. The progress of these events is subject to great individual variation."
Here, stress is viewed as a perceptual phenomenon, rooted in psychological processes. It has feedback components, making it a cyclical, rather than a linear, process. Cox proposed a five-stage model: first, the individual is presented with a demand, external or internal (such as physiological or psychological needs). The second stage involves the person's perception of these demands and an assessment of his ability to meet them. But stress is not simply an objective imbalance between demand and coping ability, but instead a subjective one: a matter of perception based on a cognitive appraisal. Even though a situation may demand too much of him, a person may work without being stressed until he becomes overwhelmed and can no longer cope. Conversely another person may be stressed by a task that they could accomplish yet feel they cannot. The third stage includes stress responses: psychological and physiological changes, à la Selye. In a fourth stage, cognitive defences and behavioural responses are developed, and in the final stage a reappraisal of the situation occurs, forming a feed-back loop that transforms the process form a linear into a cyclical one. Therefore, ineffective or inappropriate coping strategies may prolong the experience of stress and thereby promote disease.
We should, however, examine the implications of treating stress perceptually: does this imply a conscious appraisal, and if so, how does this cognitive model account for the person who develops ulcers or other psychosomatic complaints apparently without being aware that anything is wrong? It was at about this stage (early 1970s) that Hinkle argued that the whole notion of stress was no longer useful. He felt that is could be better replaced by investigations of the CNS responses to inputs. "These mechanisms are either understood or potentially understandable on a straightforward physiological basis. It is not necessary to invoke a special variable called "stress" in order to understand their occurrence. In fact, it seems illogical to do so. It is hard to think of a single general state of the living organism which could evoke such a wide variety of internal reaction patterns that are so closely attuned to coping with the internal and external disturbances which initiate them." (Hinkle, p. 43).
Lazarus & Folkman (1980s) viewed stress in a systems manner, in which none of the variables alone is capable of explaining the emotional response. They took stress to be a convenient term to describe the operation of many processes that occur when demands tax (or exceed) the person's resources. During this process, the person appraises the encounter as relevant to well-being, engages in coping processes and responds cognitively and affectively to what is happening. In this view, the idea of environmental stressors (as in the stimulus model) loses its value: a traffic jam may be viewed by some but not others as frustrating and stressful, so it cannot be classified unambiguously as a stressor:
"there is simply no way to define an event as a stressor without referring to the properties of persons that make their well-being in some way vulnerable to that event. If one accepts this reasoning, it is counterproductive to keep trying to reify the environmental input as a stressor, and it is essential to find principles for predicting the stress response from the person-environment relationship, and from the rest of the variables and processes that influence the outcome." (Lazarus & Folkman, Cognitive theories of stress and the issue of circularity. In Appley & Turnbull, 1986).
Here, stress is seen as a relational phenomenon: it only exists in the context of a person-environment interaction, and we cannot separate the two elements in defining stress. "Man participates in determining the type and intensity of stress." (Christian & Lolas, 1985)
5) Problems in Stress Measurement
The interactional model of stress that recognizes individual differences in stress reactivity produces considerable challenges for measurement. First, there is the issue of circularity. By defining a stressor as anything that produces a stress response, we are inevitably find correlations between exposure to stressors and stress responses, and we cease to investigate events that turn out not to be stressors; it produces an airtight explanatory system that is immune to disproof. "With a collection of vague definitions and mediating constructs, it is possible to account for any finding after the fact, but one really has a weak and flabby theory that does not permit one to make predictions." (Wills & Langner: page160).
To avoid this circularity. Dohrenwend therefore argues the need to use objective measure of stress (e.g. life events scales). This, however, entails returning to a more rudimentary model of stress in terms of simple Stimulus → Response without feedback loops, removing the possibility that symptoms of stress may themselves become stressors. We may also note, in passing, that attention has to be paid to choosing between subjective measurements of disease (e.g. symptom checklists), and more objective indicators (biochemistry) as outcomes in stress research. Ideally, both objective and subjective measures would be used, but this does not show which was cause and which was effect.
We have also tended to focus on over-simplified measurements, with heavy emphasis on the life event measurement traditions. Acute "events" are easier to recognize and measure than chronic stresses or ‘daily hassles’: it is easier to judge whether or not a specific event has occurred than it is to assess ongoing stressful situations. Events are often external to the individual; recording a chronic stressful situation tends, for example, to bring into question the respondent's sanity in continuing to endure the situation, which may encourage them to ignore it. If we identify a link between death of a spouse and depression, for example, we would probably interpret this as the death having precipitated the depression. But which comes first in the relationship between marital stress and depression? Most measurements of marital stress rely on subjective reports, so we cannot ascertain whether is was actual or perceived marital stress that led to the depression, or whether the depression led to a distorted perception of the marriage, and to an increase in marital stress. Because of such difficulties, researchers have preferred life events as indicators of stress. (see Kessler et al: 538-9). Lazarus and Folkman expressed the problem thus:
"In the name of scientific rigor - that is, to eliminate redundancy - researchers are often urged to measure stress by means of pure environmental events, uncontaminated by perceptions, appraisals, or reactions. This would mean abandoning the hard-won insight that there are no environmental stressors without vulnerable people whose agendas and resources influence whether or not there will be stress, the form it will take, and its short and long-term outcomes. (...) To speak of stressors in an objective and normative sense is to ignore the inevitable and extensive individual differences in response to similar environmental conditions." (in Appley & Turnbull:69).
Lazarus and Folkman introduced the Daily Hassles scale in 1980 largely as a reaction against the inclusion of major life events as causes of illness and disease. They hypothesized that small stressors are more common, and chronic low-level stressors may play a more significant role in the development of pathology. The hassles scale includes experience of feelings such as concerns over future security, time pressure, work pressures, household problems, concerns over oneself, financial responsibility, environmental problems. The hypothesis concerning the greater cumulative impact of low-level stressors has largely not been borne out by research.
There are occasional examples of contamination in the measurement of stressors. Cohen et al (1983) presented a "global measure of perceived stress" that correlated well with outcome measures of symptoms. However, items in the stress measure included negative feelings and reactions over the past month–in effect, another measure of psychopathology. A very similar problem has identified by Dohrenwend & Shrout (American Psychologist 1985;40: 780-5), when they noted that the daily hassles scale includes several items confounded by symptoms of psychological distress.
Stress reactivity varies from person to person (witness the phrase "hot reactor"). Some diagrams produced by Brunner and Marmot illustrate this. Note that these patterns of stress reactivity are sometimes held to be inherent characteristics of individuals, and other times the result of prior stress/stressor exposure.
Link to References;
Outline of biology of the stress response
PPT presentation on stress by students of 2004 class
PPT slides on Stress and Coping by Dr. J.L. Jarry (U Toronto, 2002)
Stress and stress management for university students: presentation by Nisrine, 2013
Chapter on Stress and Anxiety
Centre for Studies on Human Stress in Montreal has interesting resources; worth browsing!
Course Outline || Index of Course Notes || Reading list