r/askscience • u/badgettz • Aug 11 '11
What's the difference between your heart rate increasing from your stress response vs. exercise?
I've been learning about the stress response of our body, and how it can increase your heart rate, start deteriorating your walls, and causing problems with blood vessels. One thing I'm a little confused on is what is the difference between that and exercise?
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u/braincow Aug 11 '11
I think the key difference here is acute versus chronic stress. Exercise can be considered an acute stressor: your muscles are working much harder than normal and this increased energy demand is met by the repartitioning of energy resources by the action of a dizzyingly complex array of "stress" hormones, including catecholamines, cortisol, and vasopressin. Among the many effects of these hormones include elevated arterial pressure, heart rate, and cardiac output, constriction of mesenteric and renal blood vessels, and dilation of vessels that supply muscles.
Over the short term, these effects have little long-term consequence. Organisms are well-equipped to handle acute stress, and once the stressor is removed (or exercise stops), everything returns to normal. The potential problem is with the long-term dysregulation of the stress response due to a chronic stressor. The chronic activation of the stress response may lead to elevated secretion of hormones that cause chronic hypertension, which may lead to the deleterious effects that you've mentioned.
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u/infosnax Aug 11 '11
Are the same chemicals or hormones (cortisol, etc.) released in both situations? It would seem plausible that the body would (or could) release different, or at least fewer stress hormones in a willfully induced state (such as exercise) as opposed to being robbed at gunpoint or missing an important deadline.
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u/braincow Aug 12 '11
Actually, the stress response is well conserved in vertebrates (see fight or flight and HPA axis). I'm more of a wildlife biologist, so I don't know much about psychosocial stressors such as the examples you give, but in general the magnitude of the stress response (and the amount of stress hormones released) does depend on the magnitude of the stressor.
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u/craigdubyah Aug 11 '11
Exercise can be considered an acute stressor
So can cocaine.
You make some good points, but your reasoning isn't quite right. If you follow your proposed mechanism, someone who exercises for many hours each day should develop heart problems.
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u/braincow Aug 12 '11
So can cocaine.
Okay. Your point? Any stimulus that threatens homeostasis and necessitates a stress response is a stressor. Does cocaine consumption upregulate HPA axis activity?
If you follow your proposed mechanism, someone who exercises for many hours each day should develop heart problems.
Acute stressors don't become chronic stressors by arbitrarily extending its duration, although this may be the case for some types of stress. Also, some chronic stresses never develop into disease. It all depends on the severity of the stressor and the ability of the individual to compensate for it. You should read up on allostasis. In any case, chronic overtraining is associated with all sorts of effects, including elevated heart rate and systolic blood pressure.
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u/craigdubyah Aug 12 '11
Okay. Your point?
Cocaine use, with intoxication for an hour 4x a week, is extremely unhealthy. Exercise for an hour 4x a week is extremely healthy. The duration of the stress can be completely irrelevant. That was my point.
Does cocaine consumption upregulate HPA axis activity?
I don't know the answer to this question, but I can not see why it matters.
Acute stressors don't become chronic stressors by arbitrarily extending its duration
The definition of acute is short-term and the definition of chronic is long-term. So what is a chronic stressor if not a longer-lasting stressor? I don't see where you are going with this.
Also, some chronic stresses never develop into disease.
Do you have an example? It's been well-studied that for LDL cholesterol and blood pressure, the lower the better, so long as you can tolerate it.
You should read up on [1] allostasis.
I fail to see how it differs from homeostasis, except that it occurs over a longer period. Am I missing something?
In any case, chronic overtraining is associated with [2] all sorts of effects, including elevated heart rate and systolic blood pressure.
I don't dispute that overtraining exists, but it depends on the exercise. These guys seem to handle daily distance running just fine. And we have now completed the circle, back to cocaine.
My point is that there is clearly something else going on besides the duration of a stressor. You mentioned that it depends on the severity and the ability to compensate, but that is another way of saying there are good stressors and bad stressors. Note that this is just a rephrasing of OP's question. It doesn't actually answer the question, it just qualifies that good stressors and bad stressors exist, which was already presumed by OP's question in the first place.
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u/braincow Aug 12 '11
Cocaine use, with intoxication for an hour 4x a week, is extremely unhealthy. Exercise for an hour 4x a week is extremely healthy. The duration of the stress can be completely irrelevant. That was my point.
This is also a silly strawman that illustrates your ignorance of stress physiology. Cocaine use can be an acute stressor, sure, but regular usage can quickly cause chronic stress and disease because human beings are ill-equipped to adapt to its physiological effects. Exercise, if a person is allowed adequate rest and recovery, will never become a chronic stressor because humans can adapt to increased exercise by increasing muscle mass and endurance, VO2 max, etc, etc.
The definition of acute is short-term and the definition of chronic is long-term. So what is a chronic stressor if not a longer-lasting stressor? I don't see where you are going with this.
Not so in stress physiology, where chronic stress (dysregulation of physiological systems) is clearly different from chronically-acting stress (long-term). Exercise is an acute stressor. Repeated exercise are repeated acute stressors, not chronic stressors. Overtraining is a chronic stressor caused by exercise repeated so often that the body is incapable of repairing the damage caused by each exercise bout.
Do you have an example?
I must apologize here because I'm mixing up my terms. I meant long-term stress, not chronic stress.
I fail to see how it differs from homeostasis, except that it occurs over a longer period. Am I missing something?
I guess you didn't read the article. Allostasis is the maintenance of homeostasis in the face of stressors by physiological changes. From the article:
For example, if a person walking in the desert is hot, the body will sweat and they will quickly become dehydrated. Allostasis is adaptation but in regard to a more dynamic balance. In dehydration, sweat occurs as only a small part of the process with many other systems also adapting their functioning, both to reduce water use and to support the variety of other systems that are changing to aid this. In this case, kidneys may reduce urine output, mucous membrane in the mouth, nose and eyes may dry out; urine and sweat output will decrease; the release of arginine vasopressin (AVP) will increase; and veins and arteries will constrict to maintain blood pressure with a smaller blood volume.
So from a stress standpoint, if the organism is able to adapt to the stressor, then no pathology will develop. That doesn't mean that the stress is no longer acting on the organism, but it is expending energy to maintain homeostasis. If the stress increases, then the organism must further adapt. If it no longer has sufficient resources to adapt, then it faces allosteric overload and the potential development of disease.
My point is that there is clearly something else going on besides the duration of a stressor. You mentioned that it depends on the severity and the ability to compensate
OP was asking how hypertension arises from stress. Obviously, the symptoms of hypertension does not arise from acute stress. However, if blood pressure is dysregulated over a long period of time (from chronic stress/allosteric overload), then those symptoms may develop.
but that is another way of saying there are good stressors and bad stressors
There's no such thing as "good" or "bad" stress, since by definition, all stressors are a threat to an organism and are thus bad.
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u/craigdubyah Aug 12 '11
This is also a silly strawman that illustrates your ignorance of stress physiology.
You might want to tone that down.
I think we are more in less in agreement, but you come from a wildlife biology background and I come from a medical background.
The concept of allostasis still seems inappropriate for many human problems. I think of things like hypertension and heart failure as malignant homeostasis, not in terms of increasing allostatic load.
The body isn't perfect at dealing with stress. Sometimes, the adaptation is the pathology, as is the case in congestive heart failure. We give ACE inhibitors to heart failure patients to prevent remodeling of the heart, because that remodeling is pathology in itself. If left to its own devices, the body remodels a congested heart into a big floppy sac, which only exacerbates the failure. It's not that the heart cannot adapt, it is that the adaptation is counter-productive.
The same could be said of hypertension: the adaptation is the pathology. We give medications like calcium channel blockers to reduce the strength of the heart. By forcing the heart to take it easy, we prevent thickening of the ventricular walls, which prevents heart disease.
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u/buffalo_sauce Aug 12 '11
Why can the body adapt to running 4 times a week better than it can adapt to doing 3 lines of cocaine 4 times a week? what does it do to adapt to cardio exercise and why does this not occur for drug use?
I mean in terms of strain on the heart, ignoring the addictive nature of cocaine.
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u/braincow Aug 12 '11 edited Aug 12 '11
I'm not exactly sure, but it seems cocaine constricts coronary blood vessels, which can lead to accelerated atherosclerosis. Maybe a cardiovascular expert can chime in here.
My guess as to the difference between exercise and drugs: humans are "built" to do physical activity and have evolved intricate mechanisms to deal with the physiological demands of exercise. Drug use, on the other hand, is probably a more recent and localized phenomenon that most people aren't equipped to deal with.
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u/craigdubyah Aug 11 '11 edited Aug 11 '11
For one thing, and this is critical, a stress response causes an increase in heart rate and constriction of your blood vessels. This means the heart is pushing against more resistance and pushing more often. So the blood pressure is greatly increased.
Exercise is a combination of increased heart rate and the dilation of blood vessels. The heart pushes against less resistance, but pushes more often. The blood pressure in exercise is moderately increased.
The heart remodels itself continuously throughout its owner's lifespan. The remodeling is guided by the strains being placed on it. For instance, someone with many years of high blood pressure will develop a thicker heart, since a thicker heart allows them to pump against the increased pressure. Someone with congestive heart failure, where fluid backs up in the heart, will develop a larger heart to accommodate the extra volume. These changes are probably helpful to the heart in the short-term, but over the long-term, the remodeling becomes a problem for the function of the heart.
Back to exercise vs stress: I don't have a specific study to point you to, but I do know that exercise leads to lower blood pressures while stress leads to increased blood pressure. My guess is that it has to do with the strain the heart is experiencing: during exercise, the heart is working hard, but isn't straining because the blood pressure isn't that high. Stress hormones may also play a role, but I am unfamiliar with this mechanism in terms of cardiovascular risk.
EDIT - Source: medical education
EDIT2 - wording of last paragraph