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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, light therapy (LASER, LED), 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, massage, and vibration use mechanical energy to produce a therapeutic effect.

Many clinicians choose to incorporate the use of therapeutic modalities into patient treatment. A clinician can choose from a variety of therapeutic modalities. How a clinician chooses to use a therapeutic modality is an individual decision. The choice must be based on a combination of theoretical scientific knowledge, practical experience, and information found in the literature that provides sound research-based evidence that must be used to guide the clinician in their clinical decision-making. When used appropriately, therapeutic modalities can potentially be an effective adjunct to various techniques of therapeutic exercise and thus may enhance the likelihood of achieving a positive patient outcome.


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.

Forms of Energy

In physics, 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, photobiomodulation or light therapy (LASER, LED), and ultraviolet light therapy utilize electromagnetic energy. Thermotherapy and cryotherapy transfer thermal energy. The electrical stimulating currents and iontophoresis utilize electrical energy. Ultrasound and extracorporeal shockwave therapy utilize sound energy. Intermittent compression, traction, massage, and vibration utilize mechanical energy (Table 1–1...

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