Stress is commonly defined as the body’s responses to the demands placed… — Page 129, Lesson 196

Let’s start with the definition that sits at the heart of this whole chapter. Stress is commonly defined as the body’s responses to the demands placed upon it. Notice that word responses — it’s not just the demand itself, it’s how your body reacts. And that reaction is heavily influenced by perception. How you see a situation plays a very large role in how much stress you actually suffer. We’ll come back to that in detail later in the chapter when we look at the Stress Model. Anything that causes stress is called a stress factor or a stressor. That’s the trigger. Now, measuring stress in biological terms is hard. But the strain produced by many physical and mental stressors can be measured. You can see it in changes like a rise in blood pressure, an increase in pulse rate, changes in weight, or a change in efficiency — how well you perform a task. Your body constantly works to maintain physiological equilibrium, which is also called homeostasis. That means keeping a stable internal state despite changing external conditions. Your body has numerous mechanisms to keep the status quo — the existing balance. For example, when body heat increases, you produce sweat. The cooling effect of evaporation brings your temperature back toward normal. That’s a homeostatic mechanism at work. Physical stress happens as soon as outside conditions either put strain upon those homeostatic mechanisms, or are so extreme that they nullify them — meaning the mechanisms can’t keep up. Mental stress is much harder to measure, except in special laboratory experiments. Here’s the key point: stress is a natural requirement of life. Too much stress is harmful, but so is too little. Animals are designed to cope with their environment. If you remove all forms of external stimulation, they tend to pine away and even die. Experiments on volunteers kept for a long time in a stimulus-free environment showed that they regressed to an infantile stage and might not return to normal for a considerable time afterward. So the takeaway is this: a certain amount of stress is of fundamental importance in keeping us aware and vigilant. Too much stress will degrade the performance of both body and mind. That balance is what we’re going to explore as we move through this chapter.