STRESS

Causes and Symptoms of Stress

Causes and Symptoms of Stress

Introduction

It has been my experience, both in laboratory experiments and in clinical studies, that the term stress has not been useful. In fact, it often seems to inhibit rather than facilitate communication either among scientists or between investigators and patients. There are a number of reasons for this difficulty: First, the term is ambiguous since it means different things to different investigators; and second, there are a number of incorrect premises implicit in most concepts of stress. (Ron de Kloet, Joels & Holsboer, 2005)

Concepts of Stress

In the latter part of the 17th century, Robert Hooke discovered the fundamental law existing between an external force and the resultant distortion of an elastic body. He proposed that the change in form of the elastic body was proportional to the deforming force. However, it was not until about 100 years later that Thomas Young formulated Hooke's law precisely by defining explicit physical concepts to be associated with "change in form" and "deforming force." Young defined stress as the ratio of the force within the elastic body which balanced an external applied force, to the area over which the force acts. Thus, physically, stress is a response within an object which is inherent in its structure and which is elicited by the external force. Since any stress which is elicited from an object results in a physical change in that object, that change can be measured. For example, when the applied force is normal to the surface of an object, the object will change in volume, shape or size. These changes are called strains and are measured as the ratio of change in dimension to original dimension that is, strain is unitless. These very precise physical concepts have been adopted by a wide range of biologists. Unfortunately, there is neither precision nor consistency among these usages (Brod, 1963). For example, the concept of stress is used in its precise, physical sense by physiologists who study isolated muscles in which responses can be readily measured as physical stresses or strains; however, the terms stress and strain also are used by organ physiologists whose uses of the terms often are obscure or inconsistent with the physical definitions for example, contractility of the heart. Furthermore, the terms are used by psychologists working with whole animals where the notions of stress or strain bear only a metaphoric relationship to the physical concepts; the same terms are used by social scientists who apply them to nations or even to international institutions such as economies in contexts where they seem more like hyperboles than scientific concepts. Clearly, this spectrum of usages could in my opinion, does diminish rational discourse.

Definition

As I have already noted, Cannon defined stress as the external force, i.e., as a stimulus. Most investigators who study whole animals in an attempt to identify behavioural/physiological interactions also equate stress with the stimulus (Ron de Kloet, Joels & Holsboer, 2005). Furthermore, many scientists who study human behaviour also conceive stress as ...