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Some Notes on Stress

(Note: for references cited on this page, see the Reading List)

1) Concepts and Definitions of Stress  

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

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).

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."

Frog relaxing on a lily leaf



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.


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

"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).

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