Equis ISSN 2398-2977
Synonym(s): NMES, FES, functional electrical stimulation, EMS, electrical muscle simtulation, electromyostimulation, TENS, transcutaneous electrical stimulation, neuromuscular electrical stimulation
Contributor(s): Graham Munroe, Sheila Schils
- There are many types of physiotherapy Musculoskeletal: physiotherapy modalities in animal and human medicine that utilize an electrical current and these systems are collectively called electrotherapy devices. The varying techniques and how these systems are used, plus the bewildering array of terms used to describe them, makes comparing their indications, effectiveness and research almost impossible. There are a number of human studies which prove the usefulness of some of these techniques, but controlled clinical studies are limited in the equine field.
- Two of the similarities of all physiotherapy devices that use electricity are that they have varying wavelengths, and associated frequencies, which then all fall into the electromagnetic spectrum. For example, radio waves are approximately the length of a football field and have a low frequency, while x-rays are very short and are measured in nanometers and have a high frequency. To make matters even more confusing, there is another component called magnetism. Electromagnetic therapy Magnetic field therapy has a stronger magnetic component to the waveform than other electrotherapy devices and will not be discussed in this article.
- Basically, electrotherapy can be divided into two categories; 1. Nerve stimulators and, 2. Muscle stimulators. Nerve stimulators work by activating sensory nerves (nerves that produce sensations) and muscle stimulators act on motor nerves (nerves that produce muscle contractions. If a motor nerve is stimulated there is always an associated sensory response, but not vice versa.
- One important consideration is that all electrotherapy devices should use alternating current (AC). If a direct current (DC) is used then there is an accumulation of ions in the tissue which can result in cell damage.
- Some of the different modalities that have been discussed in the literature under the title of electrotherapy include: transcutaneous electrical nerve stimulation (TENS); and neuromuscular electrical stimulators (NMES) or electrical muscle stimulators (EMS). Transcutaneous means on the surface of the skin and almost all electrotherapy devices today are applied transcutaneously . Only electroacupuncture inserts needles through the skin to transmit the electrical signal.
- TENS units excite sensory nerves causing mainly analgesia effects by stimulating pain inhibitory systems and endorphin release. To deliver this desired effect, the pulse rate and width provided by the machine needs to be changed frequently due to the ability of the body to override the pain damping effect known as accommodation. Although TENS are not designed to cause muscle contractions, the voltage can be increased to obtain a twitch response. However the voltage to do obtain this isolated twitch is typically over 100 volts.
- NMES or EMS are a general class of electrotherapy devices where the electrical current causes depolarization of a motor neuron. These devices use a lower voltage than TENS due to the difference in the devices parameters. Care must be taken when selecting a muscular stimulator because many systems have waveform parameters exactly the same as TENS (nerve stimulator) devices.
- Functional Electrical Stimulation (FES) is a specific type of NMES. FES replicates the bodys own motor neuron signal to obtain a coordinated limb or body movement rather than isolated muscle contractions obtained by other classes of NMES. Therefore, improvements in articular and vertebral function are possible with FES rather than just changes in isolated muscle fibers or muscle tissue.
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