The Benefits of Functional Electrical Stimulation for Rehabilitation

We have known for a very long time that the delivery of certain forms of energy, including electrical, to the tissues of the body can bring about physiological and beneficial changes in those tissues.  So called electrical stimulation devices are not all the same though, as we shall discuss below.

We have learned over decades how electrical stimulation can be helpful for many neurological conditions including stroke, spinal cord injury, multiple sclerosis, cerebral palsy and for many physical medicine applications. With varying forms of electrical stimulation, we can affect muscle and nerve in order to improve muscle strength and function during physical therapy. We can relieve pain and heal wounds such as pressure ulcers - we can strengthen muscle or relax muscles that are in spasm.

This sounds pretty remarkable, but of course, the nature of the electrical energy needs to be different in these various use situations. Let’s start by looking at one form of electrical energy commonly known as FES which is associated with neurorehabilitation.

What is FES?

The RehaMove 2 FES Cycling system

Perhaps one of the reasons why clinicians have not fully embraced electrical stimulation is that the terminology is often misused and confusing. There are many types of electrical stimulation described in the literature including TENS, NMES, FES and more.

If we think of electrical stimulation as the overall umbrella term, Functional Electrical Stimulation (FES) should be considered that particular form whereby a muscle contraction generated by electrical stimulation is supportive of some functional movement. The stimulation is therefore helping a patient to perform some movement that would otherwise be absent or restricted. 

FES is a powerful therapy tool that can be used to augment exercise and support body movement in very useful ways.

An example might be the use of FES in gait training, post-stroke, when drop foot is present. Such a drop foot condition interferes with the swing phase of gait and how weight is transferred to the support leg. FES assisted walking can, in these cases, be used to initiate a contraction in the affected pre-tibial muscles to generate foot lift during the swing phase of gait.

Another example, is the case of FES Cycling. In this example, implemented in our RehaMove FES Cycling system, a muscle contraction can be generated in the major muscle groups of the legs to allow a person with an incomplete spinal cord injury and muscle weakness to actively exercise and gain strength. This system can also be used by persons with a complete spinal cord injury resulting in paralysis, in stroke or indeed many other neurological conditions. The stimulation is "functional" in that the muscle contractions are generated to be in sync with the movement of the bicycle pedals.

How does FES work?

Although FES systems come in a multitude of guises and may seem to have a wide range of features they are basically all forms of electrical pulse generators that can deliver precisely controlled electricity to the body via electrodes. In the common types of systems these electrodes will be applied to the surface of the body.

FES units that are classed as Certified Medical Devices will generally be more expensive than those sold as “exercise equipment” or perhaps on your favourite internet store. This is because the manufacturers must carry out mandatory safety testing and follow rigorous quality management procedures to ensure patient safety.

The most common forms of pulses used with FES applications will be so-called bi-polar/biphasic pulses that consist of rectangular forms of pulse with a positive and negative part. There should be no direct current (DC) part (that is used in a specific application that we won’t describe here). These waveforms will generally deliver currents of less than 130 mA, with pulsewidths of 500 microseconds and frequencies of 50 Hz or less. By varying the current, puslewidth and frequency of the pulse train, we can produce different therapeutic effects.

Surface electrodes are typically used for FES applications

The critical point is to ‘set’ the machine in such as way as to stimulate the target nerves as effectively and as efficiently as possible through the medium of the skin and muscle.

Stimulation of sensory nerves will achieve a sensory outcome, similarly, stimulation of motor nerves will bring about a motor effect. It is not possible to ONLY stimulate one type of nerve or another, but it is possible to primarily have an effect on a nerve type by setting appropriate parameters on the stimulation device.

Some electrotherapy machines in this area are specific and dedicated to a particular task (e.g. TENS for pain relief) whilst others offer numerous different stimulation modes, and a selection can be made typically from a menu system.

The RISE Stimulator uses a wet sponge and carbon rubber electrode

The commonly available systems for rehabilitation (Such as the RehaStim/RehaMove units) rely on an intact nerve structure within the muscle to work.

In cases of so-called Lower Motor Neuron injury or peripheral nerve injuries denervation can occur. In such cases, these types of neuromuscular stimulators cannot work. At Anatomical Concepts, we use a special type of stimulator - the Stimulator RISE in these cases.

This two-channel stimulator does not rely on an intact nerve structure within the muscle and instead induces direct stimulation of the muscle fibres. The RISE unit can generate higher levels of current - up to 250 mA and significantly higher pulse widths of 200 ms or more.

What are the potential risks and side effects of FES?

While FES is generally considered safe and non-invasive, there are some potential risks and side effects to be aware of. These can include local skin irritation or burns from the electrodes, muscle soreness when sensation is present or fatigue, and discomfort during the stimulation. In rare cases, FES can also cause muscle spasms or contractions that are difficult to control. It’s important to work with a professional who is trained in FES to minimize these risks and ensure safe and effective use of the technique.

There are some general contraindications such as pregnancy, cautions with stimulation over metal implants and avoidance of direct stimulation to skin wounds or tumorous lesions.

Conclusion

FES can benefit individuals with a variety of neurological conditions, including spinal cord injuries, stroke, multiple sclerosis, cerebral palsy, and traumatic brain injuries. It can also be used to help individuals with muscle weakness or atrophy due to aging or inactivity. FES is often used in combination with other rehabilitation techniques and should be prescribed and supervised by a healthcare professional trained in its use.

At Anatomical Concepts we have worked with various forms of electrical stimulation technology since the 1970’s and deal with leading products including the RISE Stimulator, and the RehaMove FES Cycling system and can offer advice and demostrations on request.