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Following completion of this chapter, the student will be able to:


  • List and describe the different forms of energy used with therapeutic modalities.
  • Classify the various modalities according to the type of energy utilized by each.
  • Analyze the relationship between wavelength and frequency for electromagnetic energy.
  • Discuss the electromagnetic spectrum and how various modalities that use electromagnetic energy are related.
  • Explain how the laws governing the effects of electromagnetic energy apply to diathermy, laser, and ultraviolet light.
  • Discuss how the thermal energy modalities, thermotherapy and cryotherapy, transfer heat through conduction.
  • Explain the various ways electrical energy can be used to produce a therapeutic effect.
  • Compare and contrast the properties of electromagnetic and sound energy.
  • Explain how intermittent compression, traction, and massage use mechanical energy to produce a therapeutic effect.


For the clinician who chooses to incorporate a therapeutic modality into his or her clinical practice, some knowledge and understanding of the basic science behind the use of these agents is useful.1 The interactions between energy and matter are fascinating, and they are the physical basis for the various therapeutic modalities that are described in this book. This chapter will describe the different forms of energy, the ways energy can be transferred, and how energy transfer affects biologic tissues. A strong theoretical knowledge base can help clinicians understand how each therapeutic modality works.


Energy is defined as the capacity of a system for doing work and exists in various forms. Energy is not ordinarily created or destroyed, but it is often transformed from one form to another or transferred from one location to another.2


There is considerable confusion among even the most experienced clinicians regarding the different forms of energy involved with the various therapeutic modalities. The forms of energy that are relevant to the use of therapeutic modalities are electromagnetic energy, thermal energy, electrical energy, sound energy, and mechanical energy.2 Shortwave and microwave diathermy, infrared lamps, ultraviolet light therapy, and low-power lasers utilize electromagnetic energy. Thermotherapy and cryotherapy transfer thermal energy. The electrical stimulating currents, iontophoresis and biofeedback, utilize electrical energy. Ultrasound and extracorporal shockwave therapy utilize sound energy. Intermittent compression, traction, and massage utilize mechanical energy (Table 1–1).

Table Graphic Jump Location
Table 1–1 Classification of Therapeutic Modalities under the Various Forms of Energy

Each of these therapeutic agents transfers energy in one form or another into or out of biologic tissues. Different forms of energy can produce similar effects in biologic tissues. For example, tissue heating is a common effect of several treatments ...

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