5.2 Defining Stress
Historical Roots
The term stress was originally borrowed from physics, where it describes the internal distribution of force exerted on any material. For example, when you apply force to a spring, the metal bends or stretches. If the force is removed before the spring surpasses its “elastic limit,” it returns to its original form. If you apply too much force to a spring, eventually, it will become permanently deformed or break.
This physical model parallels what happens to the mind and body under pressure: a certain amount of stress can be managed or even useful, but excessive or prolonged stress may lead to a “breakdown” in health and well-being.
Contemporary Definition
In modern contexts, stress is defined as the body and mind’s response to any threat, demand, or challenge, referred to as a stressor, that disrupts one’s daily life and sense of balance. Stressors may be external (e.g., tight deadlines, unexpected expenses) or internal (e.g., self-criticism, fear). In response to a stressor, the body initiates a series of physical and mental changes, such as increased heart rate, heightened alertness, and a surge of energy, to prepare the body to adapt to, or address, the stressor. These changes have been essential for humans to survive over thousands of years when faced with real or perceived danger. However, enacted over extended periods of time, they exact a cost known as an allostatic load that can accelerate the progression of disease.
General Adaptation Syndrome Model
In the 1930s, endocrinologist Hans Selye proposed the General Adaptation Syndrome (GAS) to explain how the body responds to prolonged stress (Selye, 1956). His model consists of three distinct and sequential phases:
Phase 1: Alarm
When first encountering a stressor (e.g., an upcoming exam, a sudden emergency, or a hurtful comment), the body initiates the alarm phase. This phase is also sometimes referred to as the fight-or-flight response. This evolutionary mechanism was effective at preparing early humans to survive immediate dangers, such as predatory attacks. Although modern threats are quite different, the same biological response persists. During this phase, chemical messengers called hormones are released into the bloodstream. These messengers increase heart rate, blood pressure (epinephrine and norepinephrine), and alertness (cortisol), providing an immediate surge of energy and focus.
While potent, this stage typically lasts only from a few seconds to about 10 minutes.
Phase 2: Resistance
If the stressor is not immediately resolved, the body enters the resistance phase. Sometimes referred to as the “bend but don’t break” phase, the body stays on high alert and keeps hormone levels elevated. During this phase, individuals may feel more capable and in control, even if stressors persist. For instance, a person who continues working long hours to meet repeated deadlines might feel like they have adjusted to the pace. However, this adaptation is temporary. The body is still working harder than usual behind the scenes, and without adequate recovery, energy reserves begin to deplete, increasing vulnerability to fatigue, illness, and mental burnout.
This stage can last anywhere from several minutes to many days, depending on the intensity of the stressor and the individual’s capacity for resilience.
Phase 3: Exhaustion
As time progresses, the body’s resources begin to deplete and divert less energy to other essential processes, like immune system function, cognitive reasoning, metabolism, digestion and tissue repair. Eventually, this leads to exhaustion or burnout. At this point, the body can no longer keep pace with the demands of the stressor, resulting in severe fatigue and effectively forcing the individual to rest.
Chronic stress that reaches this stage in this response can lead to serious physical and mental health concerns.
