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   Electrotherapy: TENS device    Electrotherapy: EMS device   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   Electrotherapy: electrode positioning  . 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)   Electrotherapy: FES    Electrotherapy: FES system   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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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Ravara B et al (2015) Functional electrical stimulation as a safe and effective treatment for equine epaxial muscle spasms: clinical evaluations and histochemical morphometry of mitochondria in muscle biopsies. Eur J Transl Myol - Basic Appl Myol 25 (2), 109-120.
  • Schils S J & Turner T A (2014) Functional electrical stimulation for equine epaxial muscle spasms: retrospective study of 241 clinical cases. Comp Ex Phys 10 (2), 89-97 Full Article.
  • Cheetham J et al (2011) Functional electrical stimulation of intrinsic laryngeal muscles under varying loads in exercising horses. PLoS One (8), e24258 PMC.
  • Bergh A, Nordlof H & Essen-Gustavsson B (2010) Evaluation of neuromuscular electrical stimulation of fibre characteristics and oxidative capacity in equine skeletal muscles. Equine Vet J Suppl 38, 671-675 PubMed.
  • Colson S S, Martin A & Van Hoecke J (2009) Effects of electrostimulation versus voluntary isometric training on elbow flexor muscle strength. J Electromyogr Kinesiol 19, 311-319 PubMed.
  • Salmons S (2009) Adaptive changes in electrically stimulated muscle: A framework for the design of clinical protocols. Muscle Nerve 40 (6), 918-935 PubMed.
  • Gorgey A S & Dudley G A (2008) The role of pulse duration and stimulation duration in maximizing the normalized torque during neuromuscular electrical stimulation. J Orthop Sports Phys Ther 38 (8), 508-516 PubMed.
  • Han T R et al (2007) The control parameters within the therapeutic range in neuromuscular electrical stimulation. Int J Neurosci 117 (1), 107-119 PubMed.
  • McGowan C M, Stubbs N C & Jull G A (2007) Equine physiotherapy: a comparative view of the science underlying the profession. Equine Vet J 39 (1), 90-94 PubMed.
  • Buchner H H & Schildboeck U (2006) Physiotherapy applied to the horse: a review. Equine Vet J 38 (6), 574-580 PubMed.
  • Bax L, Staes F & Verhagen A (2005) Does neuromuscular electrical stimulation strengthen the quadriceps femoris? A systematic review of randomised controlled trials. Sports Med 35 (3), 191-212 PubMed.
  • Carraro U, Rossini K, Mayr W & Kern H (2005) Muscle fiber regeneration in human permanent lower motoneuron denervation: relevance to safety and effectiveness of FES-training, which induces muscle recovery in SCI subjects. Artif Organs 29 (3), 187-191 PubMed.
  • Kern H et al (2005) Muscle biopsies show that FES of denervated muscles reverses human muscle degeneration from permanent spinal motoneuron lesion. J Rehabil Res Dev 42 (3 Suppl 1), 43-53 PubMed.
  • Porter M (2005) Equine rehabilitation therapy for joint disease. Vet Clin North Am Equine Pract 21 (3), 599-607 PubMed.
  • Xie H, Colahan P & Ott E A (2005) Evaluation of electroacupuncture treatment of horses with signs of chronic thoracolumbar pain. JAVMA 227 (2), 281-286 PubMed.
  • Kern H et al (2004) Long-term denervation in humans causes degeneration of both contractile and excitation contraction coupling apparatus, which is reversible by functional electrical stimulation (FES). A role for myofiber regeneration? J Neuropathol Exp Neurol 63, 919-931 PubMed.
  • Mirbagheri M M, Ladouceur M, Barbeau H & Kearney R E (2002) The effects of long-term FES-assisted walking on intrinsic and reflex dynamic stiffness in spastic spinal-cord-injured subjects. IEEE Trans Neural Syst Rehabil Eng 10 (4), 280-289 PubMed.
  • Lake D A (1992) Neuromuscular electrical stimulation - An overview and its application in the treatment of sports injuries. Sports Med 13 (5), 320-336 PubMed.
  • Steiss J E, White N A & Bowen J M (1989) Electroacupuncture in the treatment of chronic lameness in horses and ponies: a controlled clinical trial. Can J Vet Res 53 (2), 239-243 PubMed.
  • Gibson J N, Smith K & Rennie M J (1988) Prevention of disuse muscle atrophy by means of electrical stimulation: Maintenance of protein synthesis. Lancet (8614), 767-770 PubMed.

Other sources of information

  • Masani K & Popovic M R (2011) The Basis of Electrical Stimulation: Functional Electrical Stimulation in Rehabilitation and Neurorehabilitation. In: Springer Handbook of Medical Technology. Eds: Kramme R, Hoffmann K-P & Pozos R. Springer-Verlag, Germany. pp 877-896.
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