What is the purpose of functional electrical stimulation?
The quick answer is that Functional Electrical Stimulation, commonly known as FES, has many practical applications. FES is a widely used, non-invasive treatment technique that applies electrical impulses to weak or paralysed muscles. The idea of using electricity to have a beneficial effect on the body is not new, but it is only with advances in technology in recent years are we starting to see the true potential of this approach for neurorehabilitation and healthcare in general.
The purpose of functional electrical stimulation is usually to generate a useful (functional) muscle contraction; often with the aim of improving function and movement but, depending on the type of stimulation used, an FES device can do much more than that.
For example, sometimes FES can be used in wound healing or for pain relief. As we will see, the form of electricity used in these various use cases will be very different though.
An FES machine typically delivers precisely controlled electrical pulses through a pair of electrode placed on the skin surface. Whilst implanted electrodes might be considered for some applications this is not normally necessary for neurorehab applications. These electrode pairs act as the interface between the machine and the user's body. The electrical energy that penetrates the tissue is regulated to generate muscle activity (or the clinical goal).
In this article we review the topic of FES, some of it's applications and point to some of the devices offered by Anatomical Concepts.
Terminology
One of the issues we can encounter when trying to understand this topic is to do with terminology. Different authors tend to use different terms for what seems on the face of it, to be the same things - which can be very confusing.
To date, there isn't an internationally agreed terminology, so in this sense we should recognise that FES or Functional Electrical Stimulation is something of an umbrella term originally suggested back in the 1960's and now commonly used in neurorehabilitation where the electrical energy is aimed at achieving a functional purpose. It is not “one thing” but a family of techniques and applications. We also might see the terms “Electrical Stimulation” or “Electrotherapy” being used.
We will not tackle this thorny issue here and stick with the terms FES and Functional Electrical Stimulation as the broad application terms.
Applications of FES
There are many practical applications of FES. Some applications can be considered as using FES as assistive technology - a sort of electrical “orthosis” that is added to the body to provide a useful function when the natural function is considered to be permanently impaired.
Other applications can be considered as therapy because with consistent application of FES and the passage of time, the patient’s function can expected to improve. An example, might be in the case of wound healing or pain relief. Of course,
in some situations FES can serve as both assistive technology and therapy at the same time.!
FES can be used to help individuals with neurological conditions such as spinal cord injury, cerebral palsy, acquired brain injury, MS, Parkinson's disease and stroke. These conditions can impact upon the muscles and nerves in the affected areas.
Sometimes this results in muscle weakness, muscle atrophy (shrinking of muscle), muscle spasm, and muscle tightness, which can make functional tasks such as walking difficult or impossible.
When the nerves in the affected muscles are intact, an FES machine sends electrical pulses to the muscle’s motor nerves through the electrode pairs causing the muscles to contract. The aim is to improve muscle activity. In this sense FES can act as a form of exercise therapy, keeping the muscles in good shape and in some cases restoring function.
As an example, some individuals who experience a stroke will find that their walking recovery is impaired due a foot drop. This person is experiencing a situation where they cannot lift their foot during the swing phase of gait - this is because they cannot consciously or naturally contract their tibialis anterior muscle responsible for dorsiflexing (lifting) the foot during gait.
Many products exist for this specific application of FES. Such a product can be small and worn under clothing. Some designs might use a foot switch or an accelerometer to identify the phase of gait so that the system can decide exactly when to stimulate the necessary muscles. Basically, FES can help treat foot drop by stimulating specific muscles in the lower leg and foot at the correct time during gait, thereby lifting the foot and correcting walking function.
Another application of FES is in the treatment of upper limb weakness. Stroke patients, for instance, commonly experience weakness in one arm, and FES therapy can help overcome this, by providing electrical stimulation to the affected muscles, allowing for increased activity and muscle mass. The nature of the stimulation needs to be carefully controlled when administering electrical stimulation to avoid overstimulation of the nerves and muscles.
FES Cycling
An area where Anatomical Concepts has more than 15 years of experience is FES Cycling which involves the use of electrical currents to stimulate the muscles of the legs and help individuals pedal on a cycling machine. This innovative technology has gained popularity among individuals with lower limb paralysis who are looking to improve their physical fitness and regain some degree of mobility. Not only is FES cycling beneficial to their physical well-being, but it also provides a sense of freedom and independence that was previously unattainable.
This short video shows how and why our client, Claire Lomas, uses her RehaMove 2 FES Cycling system.
FES cycling such as that supported by a RehaMove system utilises an electronic muscle stimulation system (a stimulator) to activate specific groups of muscles of the lower limbs in individuals with paralysis. This specialised cycling technique allows individuals to use a stationary, passive/active bike to strengthen and maintain the muscles in their legs. It is generally suitable for persons following a spinal cord injury, stroke, MS or Parkinson’s disease. Unfortunately many individuals who would be suitable for this technology may not be able to access it due to the cost of systems.
The stimulation is synchronised to the movement of the bike pedals so that the correct muscles responsible for pedalling the bike are powered at the correct time. This means that the user can exercise actively using their own muscles despite the paralysis
For those with lower limb paralysis or weakness, FES cycling is a crucial tool for improving cardiovascular health, reducing atrophy of the muscles, and promoting blood flow to the lower extremities. Additionally, FES cycling can also increase neurological function and help some individuals with paralysis regain some of their lost mobility. Diligent use of FES cycling can lead to significant improvements in physical health and overall quality of life for those with lower limb paralysis.
Some versions of the RehaMove 2 support arm exercise with FES and this can be very useful when the arms are affected such as in the case of higher level spinal cord injury.
In addition to improving muscle function, FES therapy can also help alleviate muscle spasms and muscle tightness. It is a form of physical medicine and therapy that can be used as an alternative to massage therapy, whereby an electrical current is used to relax muscles.
FES Augmenting Exercise
One of the applications embedded in the RehaMove 2 FES Cycling system is something called Sequence Mode. This software is always included and allows the FES machine to be used independently from the bike and to augment other forms of exercise or therapy. For example, to support re-learning of gait as this video shows. The therapist is able to set up a sequence of muscle activations and trigger this sequence with the touch of a button. This makes it possible to fine tune the effect.
Using Sequence Mode for gait rehabilitation
Certain neurological disorders can make it difficult to control the movements in the legs when walking or standing. FES therapy can help by providing stimulation to the muscles that are responsible for leg movements, resulting in better walking function. In addition, FES can help to prevent muscle weakness, which is common in individuals with central nervous system injuries.
Sequence mode software enhances the posibilities for FES therapy. It represents a powerful tool that can be used in conjunction with other therapies to enhance their effectiveness.
Peripheral Nerve and Denervation Injuries
The examples of FES applications above rely on an intact nerve supply within the muscle to work. This is because the electrical energy is designed to activate the motor nerves which then produce the muscle contraction. However, certain types of injury, either to the peripheral nerves in a limb, or the spinal cord can damage these so-called lower motor neurons. This is also true of certain diseases that affect the nerves. The result is referred to as denervation which can be partial or complete.
The challenge now is that we need a different form of FES that does not rely on activating the muscle via it’s motor nerves. Denervated muscle must instead rely on the direct targeting of the muscle fibres to make them contract directly.
The RISE Stimulator
The RISE Stimulator and the Edition 5 Stimulator from Anatomical Concepts can both deliver the specialised waveforms that can produce useful contractions in denervated muscle.
There are important reasons to treat denervated muscle. Denervation causes changes in the structure of the muscle and soft tissues. The nerve structures disappear and the muscle will lose it’s size and the normal fibre structure will be gradually replaced with fat and collagen. Extensive research has shown that this muscle can be rescued with the right type of FES.
In cases where nerve reinnervation is expected FES can help maintain the muscle tissue structure so that it remains viable for reinnervation. If reinnervation is not expected, FES is still recommended for long term health.
In other blog articles we have explored the details of the various forms of electrical energy and how they work. In general, the waveforms used to make muscle fibres contract directly still have the bipolar, rectangular form used with FES Cycling for example but with much longer pulse widths and lower frequencies. Often the current levels may be higher with denervated muscle so a different form of electrodes are used that cover as much of the affected muscle bulk as possible.
Wound Healing and Pain
By modifying the form of electrical energy it becomes possible to encourge wound healing, for example, in the case of slow-to-heal pressure ulcers, or to relieve different types of pain. We will not explore all of the potential ways of doing this in this article. It is a topic we have covered in previous blog articles. If you have specific questions about these applications please contact us and we will be happy to advise.
Conclusion
In conclusion, FES therapy is a non-invasive, relatively safe, and well-tolerated treatment option. However, as with any treatment, FES must be administered by a knowledgeable professional to ensure the correct placement of electrodes and the correct stimulation parameters to minimise the risk of overstimulation, ineffectiveness or injury.
FES therapy is a valuable option for individuals with neurological conditions that affect their muscle function. The purpose of functional electrical stimulation is often to activate the nerves and muscles that are weakened or damaged, resulting in improved function and prevent complications such as muscle atrophy. Applications such as FES Cycling with a RehaMove system deliver stimulation in sync with the pedals of a passive/active bike.
In some cases when denervation is present, FES Can still be used if the stimulation parameters can be suitably altered. This obviously requires some knowledge of the particular equipment being usedand it’s limitations.
Furthermore, FES therapy can be used for different body parts and as a complement to other therapies. Therefore, FES therapy is an important tool in the treatment of individuals with neurological disorders.
FES therapy has shown positive results in patients with spinal cord injury, stroke cerebral palsy, MS, Parkinsons disease and acquired brain injury. It can help with muscle atrophy, muscle weakness, muscle tightness, muscle spasm, and foot drop. In stroke patients, FES cycling or FES foot drop treatment can improve walking ability and gait. The pulse duration and intensity can be adjusted to achieve the desired stimulation level and muscle response.
Along with neurological physiotherapy, massage therapy, and other physical medicine treatments, FES therapy can aid in the rehabilitation of patients with neurological disorders. FES can also help with upper limb function, as it stimulates the muscles and nerves in the arm, wrist, and hand. In addition, FES may support muscle mass retention and can prevent or slow down muscle atrophy. The ultimate function of functional electrical stimulation is to restore movement and function in patients with neurological conditions, allowing them to experience a better quality of life.