Electrical stimulation used during therapy, dates back to the ancient Egyptians who used fish to generate an electrical current to treat various ailments. Fast forward four millennia and now a vast array of electrical stimulation devices are at the therapist’s disposal. This article will focus on the growing discipline of Electrical Muscle Stimulation (EMS) and discuss its basic effects before providing advice and guidance to the paediatric physiotherapist on its application. This supports the learning that was offered at the 2016 APCP conference and the APCP neuro-disability group NMES study day held in Birmingham May 2017.
The first thing you notice when you search for information on Electrical Muscle Stimulation is the wide variety of types, methods and names, such as Functional Electrical Stimulation (FES), Functional Electrical Therapy (FET), Transcutaneous Electrical Stimulation (TES), and Neuromuscular Electrical Stimulation (NMES). Suffice to say this huge variety of terminology has left clinicians perplexed and reluctant to explore further. However, all of the different approaches named above (and many others) share the same basic approaches and rely upon the same physiological processes to work effectively.
What is Electrical Muscle Stimulation (EMS)?
EMS involves the application of an electrical current, usually across the surface of the skin using adhesive or rubber electrodes positioned on the skin in direct proximity to the muscles to be stimulated, to generate a muscle contraction. This muscle contraction takes place due to the electrical current travelling into the tissues and causing a depolarisation of an intact motor neuron that carries the signal to the target muscle through synaptic transmission to the motor end plates. The resultant muscle contraction can range from a small muscle twitch, to a powerful enough contraction to cause a physiological movement at the joint(s). This alteration of a produced muscle contraction is the result of the manipulation of the available electrical stimulation parameters controlled by the clinician. Most EMS units share the same parameters for adjustment. These are: Frequency, Amplitude and Pulse Width. The clinician requires to become confident in the manipulation of these parameters to use EMS effectively.
Electrical Stimulation Parameters
Frequency refers to the number of stimulation pulses delivered per second, measured in Hertz (Hz). At a low frequency (1-10Hz), a weak muscle twitch or flutter will be generated. As frequency is increased (more pulses delivered per second), so does the strength of the contraction created up to around 60-70Hz, at which point the frequency has more effect upon the sensory rather than motor neurons and the power of the muscle contraction reduces. EMS devices will offer a frequency within a set range (0-70Hz), some devices may only provide one set level of frequency, others will provide the option to adjust the frequency within a pre-set range. Information about the EMS device stimulation parameter range can normally be found in the instruction guide that comes with each device.
Pulse width refers to the length of time each group of pulses of stimulation is set to, measured in microseconds (us); or milliseconds on devices offering EMS for peripheral nerve damage (ms). It is common to see EMS devices offering ranges between 200-300us. Pulse width on some devices will be pre-set and on others can be adjusted. A short pulse width can be more comfortable for some patients but a longer pulse width may recruit more motor neurones and thus improve the muscle contraction produced.
Amplitude (sometime referred to as intensity) refers to the strength of the stimulation delivered, measured in milliamps (mA). The amplitude needs to be high enough to evoke the desired affect while still remaining comfortable. This parameter is always adjustable in EMS devices and often appears like a volume switch. Adjustment of this parameter is always available as amplitude may not always be set to the same level at each treatment session. As the muscle gets stronger it may require less amplitude to effect the same response, or, if the electrode position is not optimal more amplitude may be required to produce the same muscle contraction. It is therefore important for the patient and therapist to understand what level of muscle contraction is desired during each session so the intensity can be varied accordingly.
Balancing the amplitude and the pulse width can help to optimise both the muscle contraction produced and the comfort for the patient i.e. a wider pulse duration may mean the amplitude can be reduced offering more comfort.
Confidence in the use of EMS devices grows as the clinician learns to use these parameters to their advantage therapeutically; understanding what to expect as each parameter is changed in isolation or in combination. The best way to experience and practice this initially is on yourself, or on a colleague, in order to practice in a more controlled and contained environment; noticing how each dial setting affects the extent of muscle contraction, or what the stimulation feels like, so you can advise your patient before use.
Most small EMS devices are powered by household batteries, all are very unlikely to deliver enough electricity to cause harm (see contraindications below); this is more usually the number one reason therapists are not confident in applying stimulation initially. Always keep in mind you are reproducing a normal muscle contraction.
Summary of how EMS parameters affect muscle contraction
|Muscle twitch, maybe less comfortable but less fatigue. Good for heavily atrophied muscle
|Tetanic muscle contraction sufficient for physiological joint movement. Good for functional tasks
|Tetanic contraction will gradually diminish as sensory response becomes stronger. May feel more tingly distal to the electrodes
|Weak, superficial contraction but will feel less intense and will be less likely to overflow. Good for smaller muscle groups
|Stronger contraction recruiting more motor fibres but may begin to overflow in smaller muscles
|Powerful contraction, will feel deeper and more intense. Good for larger muscle groups
|Weak response but comfortable
|Stronger response but may become intolerable
*The amplitude should be increased to achieve the best possible contraction within tolerable levels. If you cannot generate a muscle contraction, manipulate the frequency and pulse width to adjust the sensory response. Remember it is often a new sensation and patient will often perceive the sensation as pain when it is just different. A good way to educate the patient, particularly a child, is to place the stimulation on yourself or their parent to show them it is ok.
Contraindications and precautions to the use of EMS
Contraindications for each device will be specified in the instructions that support each item of EMS equipment. The EMS representatives, or medics involved in the care of the patient, should also be contacted with any queries.
When considering contraindications and risks to treatment consider what may be contraindicated by a normal muscle contraction and an element of increased blood flow to the area. Electrical stimulation should not be used were active movement would not be appropriate e.g. a muscle contraction that will evoke movement around an unstable fracture. There is also not enough evidence to support the benefits versus the risks of use with pregnancy. The presence of tumours, broken skin and implanted metal work should also be a consideration and should be discussed with medical staff and EMS representatives but may be a precaution rather than an absolute contraindication. Compatibility with other types of implants i.e. pacemakers and baclofen pumps should also be considered prior to use.
Some patients may have sensation or the ability to feel the effects of the electrical current flow. In this instance EMS must be comfortable if treatment is to be successful and to be repeated. Age is not a contraindication to the use of EMS but something that may prevent you providing a second treatment to a wary child (or adult) if not approached in the right way. Comfort can be maximised by the adjustment of electrical stimulation parameters. The key message is start conservatively, you can always increase your stimulation parameters to effect a better contraction next time, but if you start too high, you may lose compliance.
The application of EMS
Once you are comfortable with the basics of delivering EMS the aims of treatment should be considered. If new to EMS, choose a simple device that offers flexibility but has some pre-set programmes to start you off. If you are more confident using EMS, consider a device with more channels of stimulation, thus allowing stimulation of multiple muscle groups with greater flexibility; this will enable therapy to be more functional. If you have a specific aim in mind, such as stepping during gait, a Functional Electrical Stimulation (FES) device that is triggered by function may be a good decision i.e. drop foot stimulation. Or if you want more channels and more whole body activity (to affect overall physical health), then an EMS cycling, rowing or stepping system may be indicated.
Whichever device you choose, there are a few considerations that are largely universal:
- Electrode selection – choose an electrode that is appropriately sized and shaped for the target area – multiple and varied options are available. More coverage of the chosen muscle will activate more of the muscle (gaining a better contraction), however too large and the electrical stimulation will leak into other muscle groups affecting the quality of your muscle action/contraction. Electrodes that adhere to the skin are generally single patient use, but rubber electrodes can also be used with contact gel and tape to secure. Single patient use/sticky electrodes require to be stored on the Teflon coated seal it arrives on and in an airtight package to maintain the stick, but will generally dry out and require replacement after a period of time (approximately 6 weeks dependent on use). Rubber electrodes require washing in between use but generally have a much longer shelf life.
- Electrode placement – different devices will provide different guidance as to where the electrodes should be placed. However in all cases try to ensure the electrodes are positioned over the muscle to be affected and you are moving the body into either anatomical neutral, or into the position with which they will assume to perform an activity. For example, if you are trying the stimulate wrist extension and place the electrodes with the forearm in pronation, if you then supinate for the therapy, the effect and movement will be changed.
- Skin surface - make sure the area the electrodes will be placed is clean and dry (moisturised/oily skin will prevent the electrodes adhering to the skin). Dense hair may need to be clipped.
- Time – As with any muscle training, a weak muscle will fatigue more quickly. Short sessions may be required initially, building to longer sessions. Some devices have pre-set programmes with pre-set parameters and session times. When considering treatment time the therapist should consider how many repetitions are achieved in each treatment session and how this compares to more conventional muscle strengthening to evoke an increased in strength or quality of muscle movement.
EMS indications in therapy
Despite the slow uptake of EMS as a rehabilitation tool in the UK there is a wealth of evidence about the effects of this type of modality for a range of neuromuscular conditions in adults and children including stroke, spinal cord injury, ABI and cerebral palsy; in some areas EMS is more evidence based than some more conventional physiotherapy adjuncts. Areas indicated for use that may impact your own patient case load include:
- Reversal of muscle atrophy and improved muscle strength.
- Support of function – i.e. stepping of the foot during gait
- Improved local circulation and reduction in skin breakdown.
- Increase / maintenance in joint range of motion.
- Reduction of spasticity / muscle spasms.
- Increase in cardiovascular function – via simultaneous activity of large muscle groups.
- Habilitation – learning new activity via movement normally unobtainable
- Maintenance of bone density
- Restorative therapy - CNS cell birth & CNS myelination
If EMS could benefit your case load, the next step is to book onto a more practical EMS course – keep an eye out for APCP run courses or make contact with your local EMS product reps for more ‘one to one’ training on the equipment they offer – most reps are very willing to come and meet you and your team and demonstrate the benefits of their equipment; some may even leave you equipment to trial for a couple of weeks.
Your EMS reps are often able to provide specific evidence to your area of work. Or why not delve into the research and compile a data base search or your own? Use this evidence to your advantage and start your journey to becoming an EMS confident therapist.
Gad A (2013) Functional Electrical Stimulation (FES): Transforming Clinical Trials to Neuro-Rehabilitation Clinical Practice – A Forward Perspective. Journal of Novel Physiotherapies. August. ISSN: 2165-7025
Kirsten Hart MSc & Matt White MSc
Clinical Specialist Physiotherapists