FORMS OF ENERGY

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. 

There is considerable confusion among even the most experienced athletic trainers 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.

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 bio-feedback, utilize electrical energy. Ultrasound and extracorporal shockwave therapy utilize sound energy. Intermittent compression, traction, and massage utilize mechanical 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 that utilize different types of energy. Electrical currents that pass through tissues will generate heat as a result of the resistance of the tissue to the passage of electricity. 

Electromagnetic energy such as light waves will heat any tissues that absorb it. 

Ultrasound treatments will also warm tissues through which the sound waves travel. Although the electrical, electromagnetic, and sound energy treatments all heat tissues, the physical mechanism of action for each is different.

The mechanism of action of each therapeutic modality depends on which form of energy is utilized during its application. Different forms of energy are generated and transferred by different mechanisms. Electromagnetic energy is typically generated by a high energy source and is transmitted by the movement of photons. Thermal energy can be transferred by conduction, which involves the flow of thermal energy between objects that are in contact with each other. Electrical energy is stored in electric fields and delivered by the movement of charged particles. Acoustic vibrations produce sound waves that can pass through a medium. Each form of energy and the mechanism of its transfer will be discussed in more detail to provide the scientific basis for understanding the therapeutic modalities.