We have all heard about the 'Fight or Flight' response in the Neanderthal context.  This basically refers to the hormonal changes  triggered when a caveman met a wild beast.  It was designed to preserve the species.  He, or she, was suddenly forced to fight the beast or leg it out and out-run or out-climb the more powerful animal.  The response being referred to involves the activation of a set of neuro-endocrine pathways designed to enhance performance in what was usually a short term yet very intense struggle.

Another, possibly more precise way of describing these neuro-endocrine responses is to characterize them as sympatho-adrenal.  'Sympatho' refers to activation of the sympathetic nervous system.  Activation of the sympathetic nervous system (SNS) causes the release of epinephrine (adrenalin) and norepinephrine into the bloodstream.  These have a panoply of metabolic actions including the elevation of blood pressure and blood glucose.  Increased propensity of the blood to coagulate is another indirect effect which would act to stem bleeding from an artery that might be injured.  Activation of the SNS also produces a rise in serum triglyceride levels.  Triglyceride-rich particles facilitate the neutralization of multiple hostile invaders such as bacteria, viruses and protozoans.  As is apparent, these responses are designed to maximize outcomes in the field of battle. 

The 'adrenal' part of the sympatho-adrenal response refers to release of the stress hormone cortisol into the bloodstream from the adrenal gland.  Because of this, serum cortisol levels rise.  Cortisol is in the category of 'glucocorticoid' hormones.  'Gluco' refers to the link with sugar and  the subsequent elevation of blood sugar levels caused by cortisol.  The benefit of enhanced blood glucose availability is that the muscles (those organs necessary for transporting you away from an angry tiger) will then have an uninterrupted supply of the fuel source they rely on.

In the past, most serious threats were usually resolved one way or another relatively rapidly.  However, in modern times the typical triggers of this primordial hormonal response are chronic in nature and thus produce a prolonged activation of the hormonal responses just described. They were never designed for chronic use.  Modern day stressors are the primary triggers of the fight or flight hormonal response.  In most circumstances stress develops not from crossing paths with a wild animal, but from the unremitting demands at home or at work, financial pressures, lack of sleep and trying to cram too much into too little time.  The hormonal responses are then activated in a continuous fashion.  The persistence of these hormonal responses is at the root of many modern day illnesses including high blood pressure, weight gain, weak bones and heart disease.  This observation is especially germane for the brain.  When exposed to persistently elevated cortisol levels, neurons suffer.  They lose contacts with their neighbors, shrink, and are less resistant to the daily insults all cells are continuously exposed to.  In rodent studies, when infused for just three weeks with the rat equivalent of cortisol, brains wither and memory suffers.  This is in only three weeks!  Imagine how many of us are exposed to chronic stress lasting for months or years.  In the animal studies, the amazing observation is that if the stress hormone infusion is stopped, the brain atrophy reverses!  If this didn't happen, there would be little more to discuss.  However, because it does reverse the question remains, "What can be done about modern brains exposed to chronic stress?"

This is where complete understanding of the flight or fight response is important.  As it evolved over millions of years, it consisted of two related phases. The first phase involves the stress response and subsequent hormonal activation.  It is followed almost immediately by the second phase, the flight response-the most likely reaction to the (generally) physical stressor.  The flight response involves running, jumping, climbing or other similar strenuous activities.  These are identical to what we refer to today as exercise!  When we exercise we trigger the same physiological responses.  They tend to counteract the effects of the stress inducer.  That is the beauty of the combination of stress and vigorous physical activity.  As a result, blood pressure falls, glucose levels fall and triglycerides fall after exercise.  Exercise even reverses the hormonal changes.  It appears to provide the best and most natural antidote for stress.  When the two phases of the fight or flight response are dissociated, or uncoupled, and one is engaged without the other (the situation occurring in most of us today) we experience only the bad effects and it takes its toll on our health. Hence, the optimal way to reverse the ill effects of our stressful lives and the associated adverse impact on our health is to exercise vigorously on a daily basis.  By understanding our ingrained physiology (the fight or flight response) and what goes awry when it is only partially turned on (especially in a continuous fashion), it is clear what the best approach is to address the problem.  Daily exercise is Mother Nature's solution to one aspect of our modern day lifestyles.