At some point, too much stress begins to affect your ability to think clearly which, in turn, affects your ability to make good decisions. One poor decision followed by another poor decision is a setup for disaster. That is why it is crucial to know how to assess the impact of certain stressors on your body and mind.

The Physiology of Stress

Stress is a difficult term to define because it is dependent upon personal interpretation. What is perceived as a negative stressor for one person may be perceived as a positive stressor (i.e., energizer or motivator) for another person. For purposes of this discussion, a commonly accepted definition of stress is the body’s non-specific response to demands placed upon it, whether those demands are pleasant or unpleasant (Selye, 1936).

All living organisms experience a certain amount of physical and psychological stress simply as a result of being alive. Organisms experiencing only a small amount of stress are usually at rest or asleep. A good example of an organism experiencing minimal stress would be a cat stretched out in the sunshine or a bear in hibernation. The only time an organism experiences no stress is when it is dead. All living creatures experience stress of some type each and every day, and that is why it is important to understand the relationship of stress to human performance.

Hungarian-born researcher Hans Selye (1907-1982) spent his life studying the topic of stress. Selye discovered very quickly that the human body experiences two types of stress: eustress and distress. Eustress is experienced by the body as positive stress. Common examples of eustress are laughing while watching a movie or playing with the family dog. Distress is experienced by the body as negative stress. Some common examples of distress that might be experienced by anyone are fatigue, high work load, or a life-threatening situation.

When an individual experiences distress, a natural physical response occurs. This arousal of the nervous system is commonly referred to as the “fight or flight” response. It is as old as humankind ands located in the lower part of our brain, sometimes referred to as the reptilian brain. This part of our brain controls breathing, heart rate, body temperature, and balance. The fight-or-flight response is so basic to human behavior that it can be called instinctual because it spontaneously activates whenever our brain senses danger in any form.

Sensory stimuli (i.e., stressors) are interpreted by the brain as either threatening or non-threatening. If a stimulus is perceived as non-threatening, no stress response is forthcoming. However, if a stimulus is perceived as threatening in any way, then certain protective mechanisms are triggered. In other words, the fight-or-flight response is automatically activated as a survival mechanism.

Any internal or external stimulus that is perceived as a threat to the body’s equilibrium causes a physiological reaction in the body. These reactions include the release of chemical hormones, such as adrenalin, into the bloodstream, and there is a marked increase in the body’s metabolic rate. Blood is redirected away from the stomach and digestive tract to supply the muscles in the arms and legs with more oxygen. Heart rate, respiration, blood pressure, blood sugar, and perspiration all increase under stressful conditions. In short, the body prepares itself to “fight or flee.”

It should be noted, however, that many other factors besides biology go into determining if an individual fights or flees in the presence of a perceived threat. Past experience in the form of memories plays a major role in the implementation of the fight-or-flee response. Research indicates that stored memories of survival have the highest priority of retrieval in frightening situations (Everly, 1989). This is crucial for successfully coping and surviving in any extremely stressful situation.

What is a Stressor?

Stressors take many forms. However, stressors are generally classified as physical, physiological, or psychological. Any stressor is a stimulus to the nervous system.

Physical stressors include conditions associated with the environment, such as temperature and humidity extremes, noise, vibration, and lack of oxygen. Pilots deal with physical stressors all the time during flight. For example, continuous noise (like the sound of a rotor blade or propeller) can have long-term, adverse effects on not just hearing, but also on blood pressure and heart health.

Physiological stressors include fatigue, lack of physical fitness, illness, and missed meals, which lead to lowered blood sugar levels. Pilots who regularly fly long distances are especially prone to the effects of physiological stressors. A pilot may be able to exist on coffee and nutrition bars for a day or two, but in the long term such poor nutrition will affect the pilot’s body and mind.

Psychological stressors are related to social or emotional factors. Some examples of psychological stressors are a pending divorce proceeding, a sick child, a demotion at work, or thoughts of a previously frightening experience.

The Relationship Between Stress and Performance

It is now known that stress affects human performance in two important ways. In some situations, stress serves as an energizer, thereby increasing human performance. In other situations, stress serves to interfere with or detract from human performance. Ironically, too little stress can cause poor performance, and so can too much stress.

Research into human performance limitations in the last three decades shows that simple tasks are performed better under higher degrees of stress and complex tasks are performed better under lower degrees of stress. This means there is a range of moderate stress referred to as “a peak performance envelope” (Garfield,1983; Currieri 1985, 1995), wherein optimal performance can be expected – indeed, predicted — in any given situation.

Both Garfield and Currieri have independently conducted research to (a) prove a correlation between stress level and peak human performance and (b) stress level and optimum human judgment. Data gathered seems to indicate that peak performance and best judgment are most evident when the research subject’s physiological responses to the stress imposed are within certain parameters of body temperature, heart rate, and so forth – hence, the reference above to “a peak performance envelope.”
Relationship Between Stress Arousal and Human Performance

Look for Part 2 of this article in our blog

Sherry Knight Rossiter holds an ATP and CFI-I for both fixed and rotary wing aircraft. She is also a Licensed Clinical Professional Counselor, who has worked extensively with general aviation pilots who have survived aircraft accidents or other frightening flight experiences. She currently serves on the Board of Directors for the Society of Aviation and Flight Educators (SAFE) and teaches online psychology courses for Embry Riddle Aeronautical University.

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