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This chapter provides an overview of the body's physical and psychological reactions to stress and injury. It also introduces many of the terms and concepts used throughout the text. The physiological response to trauma and the subsequent healing process are affected by the therapeutic modalities described later in this book. Pain, a major factor limiting function, is presented in Chapter 2.

• Why does a text dealing with therapeutic modalities focus its initial attention on the cell? To understand the purpose and effects of therapeutic modalities, we must first gain a basic knowledge of the body's response to injury. We will see that when therapeutic modalities are applied to living tissue, we are not just treating an ankle or a knee. We are applying stress • to the cells that will influence their metabolic function and assist healing.

Few, if any, modalities actually speed the healing of an injury. The body heals the injury at its own rate. However, by treating an injury with thermal, electrical, mechanical, or light energy, we attempt to provide the optimal environment for healing to occur. But what is a therapeutic modality? For the purposes of this text, a modality is a form of stress applied to the body for the purpose of eliciting an involuntary physiological response.

Defining the term "therapeutic" is needed to understand the principles behind the application of energy to the body. To be deemed therapeutic, the stress applied to the body must be conducive to the healing process of the injury in its current healing state. The optimum conditions for healing require a balance between protecting the area from further distresses and restoring tissue function at the earliest possible time.1 The application of a modality at an improper point in its recovery may hinder, if not set back, the healing process. To complete this definition, therapeutic modalities involve the application of the correct form of energy, based on stage of inflammation, that best promotes healing.

To illustrate this concept, consider a lacerated finger. If dirt and grime are allowed to enter the cut, an infection occurs and delays the healing process by hindering the normal physiological healing response. If the area is cleaned, an antibiotic ointment applied, and the wound covered with a dressing, the healing progresses relatively unhindered. Modalities function similarly; we use these devices to influence the body's physiological functions to provide the traumatized tissue with the best healing environment.

Stresses Placed on Tissues

Any type of mechanical, chemical, thermal, or emotional force placed on the body can be regarded as stress. Although we often think of stress as only being negative, many of the "stresses" in life are positive. Indeed, to be without stress is to be without life.

Consider the various types of stressors encountered by an athlete: the cardiovascular benefits associated ...

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