Even though I’ve been reading plenty about stress (see The Stress of Life, by Hans Selye), I’ve also managed to find the time to read a few interesting studies.
Some of the studies I picked up were absolutely fascinating but I didn’t have any obvious places to write about them. My main stress posts cover the basic principles rather than more recent findings (see my first post on what is stress?). So I decided to start a reading research series, in which I’ll talk about what studies I’ve been looking at.
One of the best articles I picked up was Arousal and Physiological Toughness: Implications for Mental and Physical Health, Dienstbier, Psychological Review, 1989. It’s a review of various studies relating to the possible health benefits of periodic exposure to the fight-or-flight response.
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Why did you pick this article?
The reason I picked this article was because in all the reading I have done about stress, there is a lot of focus on the hypothalamic-pituitary-adrenocortical (HPA) axis, which produces cortisol, and not a lot of focus on the sympathetic nervous system, which generates the fight-or-flight response.
Because of their focus on the HPA axis and the adverse health issues that come along when it gets upset, scientists tend to regard stress as a bad thing. However, what we are actually saying is that chronic stress or sustained stress leading to HPA axis disruption is a bad thing. Experiencing the fight-or-flight mechanism from time to time might be a good thing.
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Occasional fight-or-flight is a good thing?
That seems to be the case, yes.
Dienstbier explains that “a contrary positive view of peripheral arousal follows from studies of subjects exposed to intermittent stressors. Such exposure leads to low sympathetic nervous system arousal base rates but to strong and responsive challenge-or stress-induced sympathetic nervous system adrenal-medullary arousal, with resistance to brain catecholamine depletion and with suppression of pituitary adrenal-cortical responses.”
That sounds complicated. What does it actually mean?
Dienstbier clarifies that “this pattern of arousal defines physiological toughness and, in interaction with psychological coping, corresponds with positive performance in even complex tasks, with emotional stability, and with immune system enhancement.”
Which is another way of saying that if you exposure yourself to occasional fight-or-flight responses, you’ll become as cool as a cucumber under fire and a lot healthier to boot.
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A quick look at the two parts of the stress response
I’m going to review the two parts of the stress response in detail next week so I won’t go into massive amounts of detail here but basically:
Sympathetic nervous system – sympathetic nervous system-adrenal-medullary arousal involves the hypothalamus acting through the sympathetic nervous system to stimulate the adrenal medulla to release adrenaline (noradrenaline is also released and the two together are often called peripheral catecholamines)
HPA axis – HPA arousal involves the hypothalamus stimulating the pituitary gland to release adrenocorticotropin (ACTH) into the blood so that the adrenal cortex is stimulated to release cortisol
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Evidence that the stress response can be beneficial
Dienstbier draws attention to the following animal studies that suggest that some exposure to stressors may generate positive results:
Researchers exposed young rats or mice to daily episodes of stimulating or stressful manipulations. As adults, the experimental animals had higher adrenal-gland weights and yet were less fearful when exposed to threats than were nonstressed control animals. See Denenberg, Stimulation in infancy, emotional reactivity, and exploratory behaviour, in Glass (Ed.), Neurophysiology and emotion
In learned-helplessness experiments, researchers showed through a series of experiments that “helpless” animals suffered from reduced central noradrenaline. But rats showed no subsequent helplessness when given a monoamine oxydase inhibitor (which prevents depletion of noradrenaline) before inescapable shock.
Researchers therefore deduced that short-term neuroendocrine depletion seemed necessary for the helplessness effect. See Weiss, Stone, and Harrell, Coping behavior and brain norepinephrine level in rats in Journal of Comparative and Physiological Psychology, 1970.
Researchers therefore reasoned that because severe acute stressors depleted brain catecholamines, then intermittent stress with recovery periods might lead to stress tolerance with resistance to neuroendocrine depletion. This was found to be the case and the researchers described their animal subjects as having been “toughened up.” See Weiss, and Glazer, Effects of acute exposure to stressors on subsequent avoidance-escape behaviour, Psychosomatic Medicine, 1975
So animal studies seem to show that so long as there is enough recovery time from the stressor, the noradrenaline levels bounce back and the animal is stronger than it was before. Sounds a bit like strength training, right?
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And does the same occur with humans?
Dienstbier investigates:
Studying American male medical students, researchers noted that higher challenge-task catecholamine increases corresponded with ego strength (adaptive capacity or stress tolerance), see Roessler, Burch, and Mefferd, in Personality correlates of catecholamine excretion under stress, in Journal of Psychosomatic Research, 1967
So it seems that the same holds true for humans, which is would be expected, as the fight-or-flight response is shared with other mammals.
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The adrenaline stress response is very different from the cortisol stress response
Dienstbier takes a moment to clarify just how important it is to differentiate between the two kinds of stress response by looking at a number of studies, including:
Researchers studied catecholamine and cortisol factors and correlated them with performance measures of Norwegian Army paratroopers. The catecholamine factor (adrenaline and noradrenaline) corresponded with written technical competence and success in jumping. The cortisol factor correlated with defensiveness and with poor performance in jumps from both the training tower and aircraft. See Ursin, Activation, coping, and psychosomatics, in Ursin, Baade, and Levine (Eds.), Psychobiology of stress: A study of coping men, 1978
Based on the above study and others like it, it seems that adrenaline and noradrenaline are increased with controllable stressors that the organism overcomes, making the organism tougher. On the other hand, cortisol is increased in response to failure and the inability to cope with the challenges.
Dienstbier extends this analysis and explains that “when stressful situations are sufficiently extended, they also lead to catecholamine depletion. However, either perceived or effective coping prevents both high cortisol levels and catecholamine exhaustion.”
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Why is the fight-0r-flight response good for you?
Dienstbier explains that it is well established that peripheral arousal affects mental processes and physical performance. But how are those impacts achieved?
Glucose availability increases after toughening – catecholamine infusion studies show higher blood glucose levels in humans after training and in comparison with sedentary control groups. See LeBlanc, Boulay, Dulac, Jobin, Labrie, and Rousseau- Migneron, Metabolic and cardiovascular responses to norepinephrine in trained and nontrained human subjects, in Journal of Applied Physiology, 1977
Catecholamine influence on muscle activity - glucose may be the fuel of the nervous system, but increases in free fatty acids (and cholesterol) and blood pressure increases are also stimulated by sympathetic nervous system-adrenal-medullary arousal
Dienstbier therefore explains that he believes that the requirements for mental coping are provided primarily by adrenaline through the mechanisms of increased blood glucose and adequate brain blood circulation.
In other words, not exposing yourself to occasional doses of the fight-or-flight response is going to mean that your ability to cope with stress is much reduced and you’ll end up reverting to the HPA axis and cortisol because you’ll perceive the stressor as too much to deal with.
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What’s the bottom line?
Dienstbier believes that “life in a mechanized world can easily result in insufficient physical demands, so that natural toughening is not fostered and the neuroendocrine systems associated with arousal are not maintained near the optimum point of their genetic ranges.”
What does this imply?
Dienstbier clarifies that this will mean that “strains are therefore likely for related systems. Obvious manifestations of such strain include weight control problems, poor muscle tone, and poor endurance in physical coping. Less obvious manifestations suggested by this model include poor psychological coping endurance (stress tolerance), susceptibility to anxiety and depression, attention and learning deficits, susceptibility to cardiovascular diseases, and reduced immune capacity.”
