Stress and Adaptation: A History of Stress and Why Stress is the Key to Growth

Each of us experiences stress, and though we all may experience stress differently, most of us know precisely when we’re feeling “stressed out.” 

Stress is a natural, unavoidable human experience, but what is stress?

Furthermore, how can we get better at adapting to stress to learn how to control it — rather than let it control us? This concept is crucial to living your best life, and we can’t wait to share the science with you.

Adapting to stress is a subject we will introduce in this post and build upon in a series of blog posts covering stress and adaptation.

We will review the history of stress, dive deep into how our body adapts to stress, and discuss the five pillars we can leverage to become more adaptable to stress and allow our body to take on more stress with less cost. This last idea is an important one because whether you like it or not, stress is the key to growth. If you want to improve any aspect of your physical or mental fitness, chase a lofty goal, or thrive as a human in a world full of chaos and unpredictability, then you must learn the skill of adaptation.

We must first understand its history to learn how to adapt to stress.

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The history of stress

The modern concept of stress was first introduced in 1932 by Walter B. Cannon in his book The Wisdom of the Body. Cannon was an American physiologist, professor, and chairman of the Department of Physiology at Harvard when he coined the term homeostasis, which he defined as the body’s way of keeping itself in balance — otherwise known as “steady state” — despite ever-changing external shocks and stimuli (stress) that try to thwart this balance.

Cannon is also credited with introducing the term “fight or flight,” which is the body’s acute response to stress. All living creatures are innately wired with this response, during which the sympathetic nervous system activates. This response enables our brain and body to do something effortful — compels us to action. Cannon theorized that the sympathetic nervous system and the adrenal glands (which release adrenaline or epinephrine) work together to maintain homeostasis under stress conditions.

Let’s take a moment to break down the physiology of the “fight or flight” response. When the acute stress response is activated due to the presence (real or perceived) of stress, your adrenal glands — located right above your kidneys — release catecholamines (stress hormones) such as adrenaline. Adrenaline causes our heart rate and blood pressure to increase, allowing more blood flow to get to our working muscles, enabling us to perform at a high level and respond with a deliberate effort to stress.

This type of stress is suitable in the context of threats — it allows us to shift into a state of high alert and action. For example, imagine a scenario where we must swerve to miss a car in oncoming traffic or perform a heroic act. This stress response is a “call to action.” 

But what happens if we are exposed to stress for too long or when this stress response is activated during “inappropriate” times?

In the late 1930s, Hans Selye — a Hungarian endocrinologist — updated our understanding of stress and some of its potentially lethal consequences.

Selye observed that a typical series of physiological reactions happened to the human body upon exposure to what he called “nonspecific threats” — a surgical injury or exposure to a noxious agent, for example. Prolonged exposure to nonspecific threats could eventually lead to permanent harm or even death. Selye modeled this process in what he called the general adaptation syndrome, or GAS, which is the sum of the body’s nonspecific reactions to prolonged exposure to stress.

GAS is characterized by three phases: alarm, resistance, and exhaustion.

To understand the three phases, let’s use them in the context of “modern-day stress,” such as a difficult work situation, something we can all indeed relate to.

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Phase 1: Alarm

The alarm phase is also called the alarm reaction; it’s a nonspecific mobilization phase, during which the sympathetic nervous system activates our “fight or flight” response so that we can deal with whatever stress we’ve been exposed to. Assuming that we survive whatever is threatening us — that huge project or difficult problem at work— this alarm phase is followed by a period of adaptation, also known as the resistance phase.

Phase 2: Resistance

The resistance phase is characterized by a complete adaptation to stress — the symptoms of the “fight or flight” response disappear. Our alarm phase can end when the project with a tight deadline is completed or we’ve solved the difficult work problem. However, during the resistance phase, our body is still working hard to adapt — producing above-normal levels of stress hormones and mobilizing fuel sources. In addition, our heart rate may be slightly elevated, and heart rate variability (HRV) may drop. In other words, our body hasn’t completely “relaxed” even though the stress has disappeared. 

But what happens if the stress doesn’t go away? That brings us to the third phase: exhaustion.

Phase 3: Exhaustion

The exhaustion phase occurs when all of our resources for adaptation become depleted — not a good scenario to be in. The exhaustion phase is when we might develop signs and symptoms of an illness or feel run down. Our “energy” has, quite literally, run out.

This brings us to the final and perhaps most important concept of the stress response — adaptive capacity, or as we refer to it, your “gas tank.”

Hans Selye hypothesized that every living organism has limited adaptation energy. Once consumed, our ability to perform and adapt drastically declines. Work, as well as other demands in life, drain fuel from our gas tank — we can’t always burn the candle at both ends, so to speak.

To confirm his hypothesis, Selye exposed animals to two different noxious agents (poisons) to initiate the alarm phase. During the alarm phase, the animals’ resistance to both agents was enhanced — part of the classic stress response. But when animals were then exposed to the two agents again during the resistance phase, their nonspecific resistance to the second agent was diminished; only their resistance to the first agent remained. 

This elegant experiment shows that when our resistance to one stressor increases (the challenging work project), our resistance to other stresses has to decrease (fighting off illness, for example) — adaptation comes at a cost. That cost is the cost of adaptation energy. In other words, prolonged stress — constant depletion of the gas tank — will eventually lead to a “letdown effect.” Following a period of chronic stress, the function of our immune system may be compromised, leading to illness. This is typically why you don’t get sick during stressful times - only after, in the fallout.

The key take-home message here is that while stress is abundant and unavoidable, it doesn’t have to rule your life. Our understanding of the classic stress response, due to the work of Cannon, Selye, and others, empower us to leverage and apply stress systematically to adapt and grow. There is no growth without stress, and if we can learn to harness the power of stress, we can thrive in uncertainty and live a healthy and fulfilling life.

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