The Science of Stress

To understand the stress response, we must possess a fundamental knowledge not only of psychology
but of physiology as well. -  George Everly

Have you ever heard stories of people displaying almost superhuman-like powers when confronted with an emergency situation? Here is the story Sarah shared in class one day:

Sarah raised her hand and told of a time when her mother and sister were out working on their farm. Her mother was driving a big farm machine designed to cut the hay that was growing in their field. She didn't see the youngster playing in the tall wheat stocks. Accidentally, she ran over her young daughter with this big farm machine. Noticing the unusual sensation as she struck her daughter, she stopped the loud engine and hurried off to see what she had run over. Realizing it was her daughter, she panicked not knowing what to do. There was no one around to help. In a moment of extreme alarm, she lifted the very heavy machine off her daughter and pulled her out with one mighty motion. Once she pulled her child out from underneath the machine, she picked her up, and ran all the way back to the farmhouse to call for help. Afterwards, the mother collapsed from exhaustion, unable to generate any energy. In those few moments of her daughter's peril, she had become superwoman.

How can we explain this super-human response that releases power and strength beyond anything we have imagined or previously experienced? What physical and psychological factors are responsible for these amazing abilities?

The Science of Stress

In the last 50 years we have seen a surge of research on stress. Chapters three and four provide a scientific foundation on principles, theories and models of stress to help you understand the physiology and psychology of stress. Discovering what actually happens in your body and your mind will help you understand the mechanics behind the stress prevention and management skills you will be learning. This knowledge on the science and theory of stress is captivating and provides strong, credible support for understanding why and how stress management techniques work. Based on this knowledge you will come to understand that you use good stress management skills not just because they feel good, but because they are good science, good medicine.

Why do you feel stress in the first place? What is the purpose of this complex interaction of nerves, muscles, hormones, organs and systems that leads to such unpleasant symptoms as sore muscles, headaches, feelings of emotional upset and a host of other side effects? To answer these questions, we need to go back a few thousand years to see what life was like back then. This will help us understand how our bodies are programmed to respond to threat and danger.

Stress and the Big Bear

Put yourself in the following imaginary scenario: Imagine that you and I live in a place and time where we find no trace of modern conveniences. We have no comfortable homes, no telephones or television, no indoor plumbing, no electricity, no cars to move us around, none of our modern day comforts. For the sake of this story, let's say that we live in caves or in huts that are out in the “wilds” of some undeveloped area.

Imagine that I have invited you over to my cave because we just killed some big animal and are having a barbeque. Several of our friends are here outside of my cave just having a pleasant time. I have supplied the group with some croquet mallets and balls and we are playing a little croquet on my front lawn. Like I said, we are having a great time.

We are thoroughly enjoying ourselves when, at some point, we notice some rustling of bushes in the distance and then, charging mightily, or hungrily, toward us emerges a huge ferocious-looking bear. This enormous creature has smelled our picnic and wants some of it for himself. He is a menacing creature that could easily put us out of commission with a single swipe of his mighty forearms.

As you imagine yourself in this scenario, one of the first thoughts that will likely pop into your mind is something like, “Uh-Oh! I am in trouble here!” “I am in danger and I am likely to experience some pain!” These immediate thoughts will be followed closely by the next thought, “RUN!” You sense the immediate need to get away from this ominous animal. You don't want to be its dinner. Your next thought might be, “I need to kill this creature to protect my family, myself, and my friends!” “Fight!”

The immediate effect of these thoughts is a physiological response that prepares the body to either run with incredible speed, or fight with incredible strength. This response is known as the fight-or-flight response.

Fight-or-Flight Response

An exciting flood of physiological processes in the body immediately takes place automatically and precisely after the initial thought of “Uh-Oh!” It is a state of physiological and psychological hyperarousal. A cascade of nervous system firings and release of stress hormones lead to immediate responses that help the person deal with danger either by fighting or running.

Harvard physiologist Walter Cannon coined the term fight-or-flight response to describe our body's automatic response when we perceive threat or danger. This is a primitive response that gives us strength, power, and speed to avoid physical harm. As you read in Sarah's story in the opening vignette, the fight-or-flight response can be activated to protect both ourselves and others when we perceive danger.

This response is amazingly complex, involving interactions between many organs and systems in our body. While it is not necessary for you to understand every detail of these complex interactions, it is important to understand the science of what is happening in your body and mind when your stress response is activated. You can use this information to guide you in developing an individualized program to prevent and manage stress.

Physiological Response to Stress

When the stress response is initiated, immediate and powerful changes come about because of the activation of a particular branch of the nervous system called the autonomic nervous system (ANS). The ANS is responsible for many functions in the body that occur “automatically” such as digestion, heart rate, blood pressure, and body temperature. The activity of the autonomic nervous system takes place completely beyond our conscious control. It is automatic.

There are two branches of the ANS that are designed to regulate the fight-or-flight response on a constant basis. The sympathetic nervous system is the part of the ANS that is responsible for initiating the fight-or-flight response. Each time we have a thought of danger or pain, the sympathetic nervous system initiates the fight-or-flight response to prepare us to handle the potential danger or pain. It is an automatic reaction. We only need to think that we are in danger and the flood of physiological and emotional activity is turned on and goes into perfect functioning to increase power, speed, and strength.

The other branch of the autonomic nervous system is called the parasympathetic nervous system. This branch of nervous activity is designed to return the physiology to a state of homeostasis, or balance, after the threat, danger, or potential pain is no longer perceived to be imminent. Homeostasis is a state of internal stability of our physiology and our emotions. The example at the beginning of the chapter of our state as we played croquet would be a good example of homeostasis. We are just enjoying things, flowing along, without emotional disturbances.

The function of the parasympathetic nervous system is to slow things down, to return us to a more calm state. During parasympathetic activity, blood concentrates in the central organs for such processes as digestion and storage of energy reserves. Breathing is slow, as is the heart rate. Blood pressure and body temperature drops. In general, muscle tension decreases. During parasympathetic activity (general relaxation) we are quiet and calm. The body regenerates and restores for future activity.

The autonomic nervous system is controlled by the hypothalamus, which is commonly known as the “master gland.” The hypothalamus receives the message of danger from the higher-order thinking component of the mind and delivers a message through the nervous system that connects, like a hard-wire neuron system, to every other system of the body. The hypothalamus also delivers a message to the endocrine system to initiate the secretion of hormones. The hormones, primarily adrenalin and cortisol, flood the bloodstream and travel throughout the body to deliver information to cells and systems that will aid in creating the ability to be more speedy and powerful, as you saw so clearly demonstrated in Sarah's story in the opening story - Real Stories, Real People.

Epinephrine (adrenalin) and norepinephrine (noradrenalin) are released into the bloodstream from the adrenal medulla. The adrenal medulla is the part of the adrenal glands positioned on top of the kidneys. Cortisol is the other key hormone released from a portion of the adrenal glands called the adrenal cortex. Together, these hormones flood every cell in the body with the specific message to prepare for fight-or-flight, for more power and speed when we are faced with an oncoming big bear.

Autonomic Nervous System Responses

Some immediate physiological changes that result from autonomic nervous system activation include:

v      Increased central nervous system (CNS) activity

v      Increased mental activity

v      Increased secretion of adrenaline (epinephrine), noradrenalin (norepinephrine) and cortisol into the bloodstream and to every cell in the body

v      Increased heart rate

v      Increased cardiac output

v      Increased blood pressure

v      Increased breathing rate

v      Breathing airways dilate

v      Increased metabolism

v      Increased oxygen consumption

v      Increased oxygen to the brain

v      Blood is shunted away from the digestive tract and directed into the muscles and limbs

v      Increased muscle contraction which leads to increased strength

v      Increased blood coagulation (blood clotting ability)

v      Increased circulation of free fatty acids

v      Increased output of blood cholesterol

v      Increased blood sugar released by the liver to nourish the muscles

v      Release of endorphins from the pituitary gland

v      Pupils of the eyes dilate

v      Hair stands on its end

v      Blood thins

v      Increased brainwave activity

v      Sweat glands increase secretion

v      Increased secretion from Apocrine glands resulting in foul body odor

v      Capillaries under the surface of the skin constrict (which consequently increases blood pressure)

There are also several processes in the body that tend to decrease in functioning when the fight-or-flight response is activated.

v      Immune system is suppressed

v      Constriction of blood vessels, except to running and fighting muscles

v      Reproductive and sexual systems stop working normally

v      Digestive system stops metabolizing food normally

v      Excretory system turns off

v      Saliva dries up

v      Decreased perception of pain

v      Kidneys decrease output

v      Bowel and Bladder sphincter close

We do not need these functions and systems to operate at high capacity to either escape from or kill the big bear. Their work is therefore suppressed in order to divert energy to those vital systems involved in increasing speed and power. For example, you do not need the immune system to help you kill the big bear. You do not need the reproductive system to help you escape from the big bear. Understanding the sympathetic and parasympathetic nervous systems response to stress is important in explaining the stress-related diseases and conditions covered in the next chapter.

Author's Anecdote

When I was a teenager, I lived in an area of town where there were nothing but homes and parks for many blocks. One part of this neighborhood had a large hedge that was about 4 feet high next to a somewhat busy street. During the winter months my friends and I would assemble behind this hedge and prepare for oncoming cars. When they came close to our location we would unload a barrage of snowballs on the unsuspecting cars. (This was how we kept our arms in shape for baseball season during the off-season.) The person who was awarded the highest honors was the one of us who could make the best “dent” sounds in the car or truck that was passing by. Even more exciting than the dent sound was the rare occasion when the car or truck would stop and the driver of the car would come chasing after us. Of course, nobody knew our neighborhood like we did, so the possibility of getting caught by even the swiftest of pursuers was very remote. But what we did notice, as we were being chased through our neighborhood, down the streets, and across the parks, was that in those times of pursuit, we were suddenly gifted with incredible speed and power. We were able to jump over high fences with ease, run down streets and through parks with the velocity of Olympians. We even noticed that in those times, our ability to see where we need to go to make it to safety (this activity always took place after the sun had set and darkness prevailed) dramatically improved. I am not very proud of those days and find myself irritated at those young teenagers who do the same thing to my car nowadays, but I learned some powerful lessons about the fight-or-flight response even in those early years. MO

The Purpose of the Fight-or-Flight Response

It is interesting that the physiological stress response has only one purpose. The fight-or-flight response is designed to help us do one thing, and only one thing, very well. That one and only purpose of this response is to help us SURVIVE! Our bodies are designed for survival. When the big bear is charging at us, our system knows how to protect us from experiencing pain and death. The mechanics for sustaining us are nearly flawless. There is no other purpose for the fight-or-flight response.

The instant we have the thought of danger this flood of physiological activity happens automatically. It is like a magic switch inside that instantly, and without our conscious command, turns on all of those systems in the body that will help us be faster and stronger. In the short run, this response is a powerful and useful process, however kept “on” for a longer period; this response can produce serious problems. You will learn about stress and disease in the next chapter.

The stress response, in a picture format, looks like this:

Notice that when we are in homeostasis, as we are when we are playing a friendly round of croquet, we are in a state of balance. Then something happens in our environment, like a big bear charging out of the forest. This perception of danger automatically initiates the fight-or-flight response. Once we sense no more danger, we experience exhaustion and fatigue because we have expended a tremendous amount of energy while running or fighting. We are exhausted but the stress response is no longer activated. Because we feel safe again, the functions in the body that activate the stress response are turned off. We gradually return to normal (homeostasis) and we are ready for more relaxing rounds of croquet.

So, physiologically, the stress response is characterized by sympathetic nervous system activation, which ultimately results in the secretion of chemicals into the bloodstream mobilizing the behavioral response. Whether the response culminates in “fight” or “flight” depends on whether the threat or stressor is perceived as surmountable. Thus, an appropriate stress response is essential to survival.

Research Highlight- Biobehavioral Responses to Stress in Females: Tend-and-Befriend, not Fight-or-Flight.

For the last five decades the fight-or-flight theory has dominated stress research. Our understanding of how the body responds to stressors has increased dramatically during this time. It is interesting to note that the biobehavioral fight-or-flight theory has been disproportionately based on studies of males. This is due in part to the fact that females experience natural, cyclical variations in hormonal and neuroendocrine responses. This can lead to confusing and often uninterpretable results. As a result, the processes involved in stress responses in females are less well understood.

A team of scientists supported by the National Institute of Mental Health formulated a theory that characterizes female responses to stress by a pattern they term “tend-and-befriend,” rather than by “fight-or-flight.” Their research supports the premise that female stress responses have selectively evolved to simultaneously maximize the survival of self and offspring. Thus, the tend-and-befriend pattern involves females' nurturance of offspring under stressful circumstances, the exhibition of behaviors that protect them from harm (tending), and befriending - namely, creating and joining social groups for the exchange of resources and to provide protection. The scientists propose that these responses build on the biobehavioral attachment-caregiving processes that depend in part on oxytocin, estrogen and other sex-linked hormones.

Additionally, literature on both human and nonhuman primates evidence substantial female preference to affiliate, or make close connections with others, under stress compared to males. The tend-and-befriend pattern likely is maintained not only by sex-linked, neuroendocrine responses to stress, but by social and cultural roles as well. This interesting, new, theoretical model opens a fresh field of inquiry in stress research.

The fight-or-flight response is generally regarded as the prototypic human response to stress. The tend-and-befriend theory you read about in the Research Highlight - Biobehavioral Responses to Stress in Females provides some interesting food for thought, however this research is still in the early stages. While we know that there may be some differences in how males and females respond physiologically to stress, we also know that there are many similarities. The fight-or-flight response explains most clearly the chain of events that occur in most people in response to stress.

The Stress Response and You

So, how does this relate to you? You have probably never been chased by a big bear, or any other wild animal for that matter. The stress response today is simply the fight-or-flight response used by our primitive ancestors as they faced the threats of daily life.

Unfortunately, our bodies still react the same way to threats - real or imagined - even though, in a vast majority of cases, the stressor does not require us to fight or flee. As Harvard cardiologist Herbert Benson remarked, “The fight-or-flight emergency response is inappropriate to today's social stresses.”

The way the stress response works in the short run is very beneficial to help us amass great strength, focus more clearly, increase our speed and perform at a higher level when the equivalent of a big bear is running toward us. We can occasionally use this immediate energy to help us when we do find ourselves in actual danger, facing potential pain or even death. Imagine this scenario that Ashley shared in class:

“My apartment mate, Julie, had left earlier in the day to spend the weekend with her family. After a quiet evening at home, I locked the doors and settled in to my cozy bed feeling safe and secure. Sometime during the night I woke suddenly and with a strange feeling that something wasn't right. There, standing right next to my bed, was a tall dark figure. My body instantly responded as I jolted from the bed and let out a scream that would wake the dead. I grabbed my lava lamp from my bedside table and flung it in the direction of the intruder. The shadowy figure turned quickly and dashed out through the open window.”

Ashley's stress response may have saved her life. The threat imposed by this stranger activated her stress response in an automatic and powerful manner.

Acute Stress

You can probably think of times when your body has responded to a danger in a manner similar to Ashley's response. Here are other examples of acute stress in which the demand, danger or threat is quick, immediate, very real, and usually does not last very long:

·      Giving birth to a baby

·      Driving down the highway and your tire blows

·      Hiking down a trail when you trip and start to tumble down a steep decline

·      During an earthquake

·      When lightning strikes

You get the point. Acute stress does happen and in the very short run and in the right amounts, an appropriate amount of tension is helpful, beneficial, and may even save your life. However, in reality, these types of experiences are a rare occurrence in daily life. Unless you happen to work in a high-risk occupation such as a policeman in the inner city, fireman, or a whitewater rafting guide, the percentage of our days that include actual threats to our lives is less than 1% of the time. Contrary to how it may look from watching the evening news, for most of us our society today is not one where acute threat or danger is a daily occurrence.

Chronic Stress

If the stress response is allowed to stay in the “on” position for more time than is necessary to escape the big bear, the result can be damage to our health. We call this state of continued sympathetic nervous system activation “chronic stress.” The diagram that we used earlier can be altered slightly to demonstrate the stress response staying “on.” It would look like this:











Instead of returning to homeostasis, the fight or flight response is activated for an extended period of time. Have you ever heard someone say that she or he seems to be stressed all the time? You are probably beginning to understand why this is a problem?

As we discussed earlier, when we have that “uh-oh” thought, the stress response turns on automatically. With this comes a flood of physiological activity designed to help us run fast and have lots of strength. However, if it is not turned off, or down, there are many unhealthy consequences.

Listen to your body. Your body is designed to give you feedback about the choices you make. For example, when a person is hung over from drinking too much the night before, the body sends messages including headache, nausea, unclear thinking, and muscle pain. On the other hand, a healthy choice like a nice, relaxing jog can result in feeling balanced, alert, refreshed, and energized. The body is sending messages that jogging was a healthy decision.

Remaining in the stress response is not healthy. The body gives us feedback about excess stress with a host of signals. Some of those signals, if not heeded, include damage to parts of the system. Although stress is not listed among the top 10 causes of death in America, it is linked to many illnesses. This does not necessarily mean that stress causes the problem, but it does mean that stress contributes to the problem.

The General Adaptation Syndrome

One of the best known biological theories of stress is the general adaptation syndrome (GAS), a process in which the body tries to adapt to stress. The general adaptation syndrome provides a summary of the physiological changes that follow stress.

Stress pioneer Dr. Hans Selye developed this theory as a result of his research on the physiological effects of chronic stress on rats. Selye observed three sets of responses whenever he injected an animal with a toxin:

·         the animal’s adrenal glands enlarged

·         the animal’s lymph nodes shrank

·         severe bleeding ulcers developed in the animals stomach and intestines

He had noticed the same types of response ten years earlier, as a medical student. Selye theorized that the same pattern of changes occurs in the body in reaction to any kind of stress and that the pattern is what eventually leads to disease conditions, such as ulcers, arthritis, hypertension, arteriosclerosis, or diabetes. Selye called the pattern the general adaptation syndrome. For decades, researchers have studied the syndrome, and Selye’s theories have held up to all levels of scientific scrutiny.

Dr. Selye identified three stages of the general adaptation syndrome:

  1. Alarm Stage - When a stressor occurs, the body responds in what has previously been described as the fight-or-flight response. Several body systems are activated, especially the nervous and endocrine systems, to prepare the body for action.
  2. Stage of Resistance - If the stressor continues, the body mobilizes its internal resources in an effort to return to a state of homeostasis, but because the perception of a threat still exists, complete homeostasis is not achieved. The stress response stays activated, usually at less intensity than during the alarm stage, but still at a level to cause hyperarousal. For example, if you learn that your mother is diagnosed with cancer, you may initially respond intensely and feel great stress. During the subsequent weeks, you struggle to carry on but this requires considerable effort.
  3. State of Exhaustion - If the stress continues long enough, the body can no longer function normally. Organ systems may fail and the body breaks down in a variety of ways. Continuous stress that causes the body to constantly adapt can become a threat to health. It is difficult to maintain a state of wellness over time when our body energy is channeled into coping with stress.


Your body is designed to respond to acute stress in a predicable manner for one outcome, your survival. This response, the fight-or-flight, or stress response, is critical for your ability to survive the life-threatening situations in life. Through the actions of the autonomic nervous system, your body is programmed for a response that will protect you from harm.

In today's world however, many of our challenges are not acute, physical challenges. Today we are faced with psychological and social stressors like too much to do, financial debt, concern for a loved one, loneliness, or unhealthy relationships. Our physiological response is not well suited to deal with these types of stressors. There are negative health consequences when our bodies stay in a state of physiological hyperarousal without release.

Understanding concepts such as the fight-or-flight stress response and the general adaptation syndrome provide you with the foundation for understanding how relaxation techniques have the ability to intercept the stress response. In chapter four you will learn more about the powerful mind/body connection and its impact on health and disease.

Key Points

*The fight-or-flight response is designed to help us survive.

*The fight-or-flight response involves a complex interaction of many body systems and organs. This response activates needed functions and minimizes unnecessary functions during times of stress.

*The autonomic nervous system is responsible for a large number of commonly occurring functions in the body that occur “automatically” such as digestion, heart rate, blood pressure, body temperature.

*The two branches of the ANS are the sympathetic nervous system and the parasympathetic nervous system. The sympathetic branch is responsible for expending energy. The parasympathetic branch is responsible for conserving energy.

*The autonomic nervous system is controlled by the hypothalamus.

*While the fight-or-flight response is critical to our survival during times of acute physical stress, this response can have unhealthy consequences during times on ongoing social or psychological stress.

*The General Adaptation Syndrome describes a process in which the body tries to accommodate stress by adapting. This process consists of three stages; Alarm, resistance, and exhaustion.


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