In my last post I introduced what stress is in a general sense and how there are various categories of stress. These categories represent types of challenges. These challenges impose a demand for energy on the body that are similar, even though the challenges themselves may seem very different. In this post I’m going to have us look more in depth at what is occurring when various challenges engage a similar stress response in the body.
All challenges which become stressful progress in a similar way in the body.
An easy example of a challenge becoming a stress is walking up a steep hill. Initially the challenge is minimal; however, as the incline becomes steeper, breathing will begin to increase, and the muscles will begin to recruit more energy to continue walking at a higher rate of force production. At some point the muscles may begin to burn, as they cannot meet the demand without recruitment of glycogen stores, and lactic acid begins to build up. At this point breathing becomes labored, and the lungs may begin to burn if the pace is maintained. This is due to the inability of the heart and liver to remove enough lactic acid from the blood before it enters the lungs. By the time you reach the top of the hill, if you do not slow your pace, you will be nearly exhausted. You will likely be sweating, feeling sick and weak, and you will collapse gasping until oxygen and glucose are able to once again re-energize your tissues.
During this process, the challenge exceeded your body’s ability to easily meet the energy demand. Adrenaline was released in order to increase the availability of energy, and then cortisol was released in order to further provide energy by breaking down tissues in order to prevent exhaustion. This is a very simple but effective description of our general stress response that delays exhaustion of the body by supplementing the energy being pulled from the reserves.
Perceived challenge engages the stress response.
In this case the stress response was engaged by the physical demand on the body. But what about mental stress? Why would it engage a similar response without the physical demand? The brain needs a constant source of energy which is primarily provided by glucose. In a fasted or underfed state, increased brain activity can bring on a significant need for glucose that must be supplied from energy reserves, and thus represents a stress response. However a more important common reason for mental stress, rather than having to think when under-fed, is having to handle a perceived challenge.
For example, when we learn of a large project with a deadline set in the near future, we may worry that we do not have the time or resources to accomplish this goal. This fear or worry triggers the primitive brain and the fight or flight 
response. This pathway was developed in order to react to potential threats, such as the smell of smoke and a forest fire, the sound of a predator in the bush, or the sight of a violent storm on the horizon. Even though the danger is not the same, we respond the same way when we see the angry boss, a professional adversary, or police lights behind us in traffic. Our bodies will act in much the same way as when we climb a steep hill. The feeling of butterflies in the stomach from anticipation, nausea from bad news, or fainting when given shocking information are all symptoms of the adaptive state from stress.
One significant difference between these perceived stresses, such as a deadline at work, and more physical stress, such as walking up a hill, is that there is a way to interrupt the progression of this stress state other than completing the task before the deadline. If we have already successfully handled similar situations, confidence can circumvent the fight or flight mechanism and allow for a more immediate return to optimal function. The response to stress is proportional to the intensity and duration of the stress. For this reason it is uncommon for someone receiving notice of a deadline at work to become short of breath and collapse to the floor, as someone would be likely to do after running up a steep hill. That is not to say that it is impossible for a mental stress to have such effect. A “panic attack” is an example of mental stress which has reached an advanced stage.
Challenges have a cumulative effect and can not truly be separated from one another.
Nutritional deficiencies that reduce the amount of available energy or the ability to generate needed proteins can also create a stress in the body. Poisons, such as snake venom, brought into the body from the environment will provide a toxic stress. Those two are examples of stressors that seem to fit well into separate categories. It is fairly obvious how individually they will each present a challenge to the body that creates an inability to easily meet the demand for energy. The nutrient deficiency reduces the body’s ability to regenerate the needed tissues and will require the breakdown of less fundamental tissues to meet the need. Similarly, the snake bite will decrease the body’s ability to generate energy due to demands placed on the body to counteract the effects of the venom.
While these are clear cut examples of a single challenge becoming a stressor in an isolated manner, it is important to also understand how these various varieties of stress are related and can instigate each other. For instance, when you are in need of energy, and the food eaten is difficult to digest, the energy needed for digestion may not be easily available and this will trigger a stress response. In that example, the act of digestion produced a physical challenge, so it is, in a sense, both a nutritional and a physical type of stress.
A toxic stress may be induced by other challenges, like the stress of exercise. At all times, there is a normal amount of microbial organisms living in the lower portions of the small intestine of humans. These natural flora and fauna are composed of bacteria, yeast, and other germs. They are considered by some experts to be potentially beneficial; however, even the germs that are present in the healthiest individuals “leak” materials called lipopolysaccharides. Lipopolysaccharides are highly toxic to the body if they cross the intestinal wall and enter the bloodstream. These toxic by-products can more easily cross the intestinal wall when the blood flow to the gut has decreased due to intense physical activity. So, while this challenge is always present at some level, there is an acute increase in stress due to this bacterial toxin challenge whenever the intestine is poorly nourished. These relationships between challenges and their cumulative effect will be important when we explore chronic stress in future posts.
The way I like to summarize the effect that significant stress has in the body is:
When under significant stress, the body sacrifices its life accelerating functions, such as digestion, some organ function, cellular regeneration, cognitive function, and general energy production. At the same time the death inhibition mechanisms are engaged, such as muscle action, sight, hearing, smelling, and proprioceptive function.
Stress is an important part of our developmental process.
It is important to understand how stress can be beneficial. If a stress can be overcome quickly, the body will relax and begin restoring the energy reserves used during the stressed state. Once the body is re-energized, any damaged tissues will be repaired by the immune system. The body does not stop the adaptive response to stress upon regaining its pre-stress, functional state. In fact, once the body has been fully restored, there will be a super compensation characterized by an over adjustment of energy reserves and needed function of the necessary tissues. In this way the body will increase its ability to meet a similar challenge in the future without undergoing a stress response. This response to acute stress is one of the ways that the right exercise program helps us to grow stronger and healthier.
What would happen if we were not able to adapt to stress at all?
Well, in animals and humans with compromised or removed adrenal glands, any acute stress, including low blood sugar from skipping a feeding, will result in a cascade of events called shock. During shock the cells are unable to meet the energy demand needed to stay alive. The blood will become toxic and nutrients will be unable to be delivered, resulting in death. In these cases a large dose of adrenaline or sugar can sometimes interrupt the shock state by re-energizing the cells and restoring the natural state of function. This is a way to understand that the need for energy is central to the effect of stress in the body. However, neither sugar nor adrenaline administration can cure all cases of severe stress, such as when a person suffers a heart attack or stroke.
How much stress is the “right amount”?
It is hard to say exactly what the optimal amount of stress is for each person, as it will vary greatly depending on that person’s state of health and a number of environmental factors. However, there is definitely an amount of stress that is too much, even in a very fit individual. Any stress that leads to sustained production of high levels of cortisol is likely to be detrimental. So, we are really looking for the “sweet spot” regarding stress. We want as little as is needed to get a beneficial, life-enhancing response from stress. It’s a bit like Goldilocks and the Three Bears—we want the amount of stress that is “just right” for us.
Even if you are a very healthy person who can meet the challenge of most significant stresses, some stresses are so severe that you will not be able to handle and recover from them. Examples of such stresses include gunshot wounds, septic shock from severe bacterial infections, and anaphylactic shock from a severe allergic reaction. On the other end of the spectrum, some individuals in severely weakened condition will easily be overwhelmed by challenges which seem mild to the average person. Many of these individuals have a high level of stress in their lives at all times and have been over-utilizing their defensive mechanisms. In this exhausted state, cortisol will not be able to be produced in sufficient quantities, so for these individuals any stress will become overwhelming in short order. This will be described better in a future post on chronic stress.
So we have now thoroughly reviewed what stress is, how the body responds to acute stress, and why it is important that we are able to respond in this way in order to prevent death. Stress is an everyday part of our lives, and the foundation of any plan for increasing general well-being should be centered around the reduction and management of stress. Although we often emphasize the negative effects of stress, stressful experiences can also be entertaining and enriching. Some level of stress is a part of everyday life, helping us to become better equipped to handle future challenges. In fact, Hans Selye, the scientist who did the greatest work in understanding the body’s reaction to stress, said, “Stress is the spice of life.”
In the next post on stress, we will discuss how chronic stress hampers our ability to respond effectively to challenges, both physical and mental.
