What is FES cycling?

Introduction

This story is about how to exercise paralysed limbs despite having experienced a spinal cord injury or other neurological condition (including stroke, MS, Transverse Myelitis and more). Spinal cord injury can lead to paralysis which can restrict exercise participation. Fitness can reduce and the risk of health complications and illness are likely to increase. As we will learn, FES Cycling is a method that allows active exercise of the limbs despite their paralysis. The origins of this approach are rooted in the past but the technique has an excellent research pedigree and this technology is widely used in homes, clinics and hospitals around the world.

Electrical stimulation of muscle

Electrical stimulation of paralysed muscle has a long history. In the 1870s, the French physician Duchenne was using electrical energy to make leg muscles contract and therefore initiate standing with his paraplegic patients. Of course the technology available was limited by todays standards.

The use of electricity to provoke effects on the body has long been of interest. Duchenne and many clinicians since, have relied on the fact that skeletal muscle can be made to contract by the local application of patterns of energy; including small amounts of electrical energy as we will discuss shortly.

FES Cycling

Today, electrical stimulation is widely recognised as a powerful and safe tool that has a number of practical applications in physical rehabilitation. We will restrict our discussion to the one application when we combine a programmable, functional electrical stimulation unit with a motorised bike; sometimes called an FES bike, FES Cycle or FES Cyclingsystem.

Whilst motorised bikes that can move paralysed legs with passive cycling are popular and they do help prevent joint contractures, the addition of FES ensures that exercise is active and this has a more powerful health benefit.

Research and development in the art of cycling using functional electrical stimulation (FES) of the paralysed leg muscleshas been going on in various parts of the world for around forty years now.

It was established in the early 1980s that people with paralysed limbs due to a spinal cord injury, including patients with a clinically complete lesion, are able to propel a cycle by means of controlled, sequential stimulation of the large leg muscles.

For example, various combinations of leg muscle groups - at least the quadriceps and hamstrings - can be activated in order to achieve an effective cycling action. Each muscle group is "switched on" during only part of the 360 deg crank rotation, to ensure that stimulation of each group results in a positive crank moment. This is achieved by synchronising the delivery of muscle stimulation to the movement of the bike pedals.

This is usually achieved using a continuous measurement of the bike's crank angle during cycling. An FES bike typically monitors the speed of the pedals and the effort generated by the user and uses this information to modulate the stimulationdelivered to the muscles. Products like the RehaMove system allow the user to set a target cycling speed and level of resistance to pedalling. This allows the user to get stronger over time.

FES Cycling Basics

The FES unit constantly monitors the position of the pedals as well as the cycling speed and whether power is being generated. The units software can then decide which muscles need to be stimulated

Most products are available in a form that will also allow upper limb exercise too and utilise the arm and shoulder muscles if these have been affected by the condition. There is even a version that allows a person lying in bed and in intensive care to use FES Cycling and there are many benefits of this.

FES Cycling is commonly used by people with a spinal cord injury in the UK, but it has also been applied in people with lower-limb dysfunction in a range of other neurological populations such as adults after stroke, or with MS, Transverse Myelitis, Parkinsons Disease and children with cerebral palsy. The outcomes and benefits of course vary a great deal with the condition.

A range of physiological benefits has been observed in clinical studies of subjects with spinal cord injuries, including improvements in cardiopulmonary fitness, muscle strength and bone density. Sometimes FES Cycling helps to calm muscle spasms. Several commercial systems are now available for stationary exercise including our own RehaMove system.

The majority of our clients have experienced a catastrophic injury and are using these systems at home several times per week. Although these FES Cycling systems can help any of the conditions mentioned above, cost is often a barrier to access unless the person has access to insurance or funds via a medico-legal claim. It is widely recognised now, thanks to extensive research, that regular use is beneficial to long term health.

RehaMove 2 FES Cycling system based on the MOTOmed Loop LA

Who can and cannot use an FES bike?

There are a wide range of suitable conditions as we mentioned above. Just as with any medical product there are also contraindications and some cautions to using them. These include things such as active fractures in the limbs being exercised, joint contractures that prevent a cycling action, pregancy and the presence of certain types of implanted medical devices. Contraindications will tend to vary over time and with developments of the technology but these should always be checked in each individual case.

Some types of spinal cord injury result in what is called denervation of the leg muscles. The peripheral nerves to and from the legs branch from the spine around a particular vertebral level. If there is injury around that level it can disrupt the nerves locally resulting in denervation. This type of electrical stimulation cannot then be used in many cases (Although we have other technologies that can help in these circumstances)

When the upper limbs are to be exercised with FES it is important to verify the integrity of the shoulder joints. When indicated, this exercise can be fine tuned to preserve shoulder function and prevent contractures in the upper limbs.

How much electricity is being used?

The amount of electricity is very small. Technically, the electrical waveform used will normally be a bipolar, rectangular pulse. The maximum current will be around 130 mA. The FES unit that makes the muscles contract delivers stimulationto the surface of the limbs via two surface electrodes placed on the limb segments with a gap between them. The current flows in to the tissues via one electrode and out via the other one and in doing so, providing the amount of energy is sufficient, activates the nerves that bring about a muscle contraction.

How muscles are activated

There are other stimulation parameters to consider beyond current; namely pulse width and frequency. The combination of current, frequency and pulsewidth can be varied by the FES unit to influence how strong the muscle contraction will be. Some products will vary some of the parameters automatically within safe limits and of course allow the user to make changes.

If we look at the electrodes and tissues in a different way - as an electrical circuit - we would see that the skin and epidermis are “insulators” which are capacitance in electrical terms. The skin has hair folicles that allow some current to flow into the deeper, moist tissues and these result in the resistance shown in parallel to the capacitor. Designers of FES units take these electrical properties into account in their design process.

The skin and deeper tissues are part of an electrical circuit

What does FES feel like?

Many of our clients have an injury which means they have little or no sensation in the area in which the electrodes are applied. So nothing is felt. This doesnt mean that you can make the stimulation as strong as possible as there are other things to consider. For example, you need to be aware of skin irritation at the electrode sites and provoking muscle fatigueresulting in a metabolic insult, by having the intensity of stimulation too high.

With some users who have sensation, the level of stimulation can be reduced to reduce any discomfort. We have met some people who find it difficult to tolerate useful levels but this is quite unusual.

With some levels of injury, (above T6 level) care must be taken, especially at the beginning of use, to avoid autonomic dysreflexia which is a dangerously high spike of blood pressure. Most people who might be susceptible to this condition will have learned to recognise how the onset of this feels at an earlier stage of rehabilitation. If someone feels unwell when using a FES bike this should be halted immediately.

It's a good idea to ensure that bowel and bladder are clear before exercising.

Can you build muscle with electrical stimulation?

Regular training with a RehaMove system or other FES bike will definitely encourage growth of the leg muscles and fight off muscle atrophy. By varying the stimulation parameters, lower limb muscles can be conditioned for endurance or power.

Although the technology has improved over time, it is less efficient to trigger a muscle contraction using FES than it is for the body working "naturally". The body has a much more efficient process for recruiting muscle fibres to contract. It is unlikely that someone starting to use an FES bike for the first time will generate much power. It takes time and patience - think - more of a marathon than a sprint.

Stimulating the gluteal muscles during cycling can help reduce the risk of pressure ulcers. Some clients will use the FES unit of the RehaMove system independently from the bike with software called Sequence Mode that allows other forms of exercise to be augmented with FES. We can use this software in lots of ways including wound healing (dealing with pressure sores) or things link shoulder stabilisation (shown below) We will cover this application in future articles.

Sequence Mode software allows many applications

Does electrical stimulation relax muscles?

Some users have troublesome spasms in the legs. These can be a nuisance and often medication is offered to try and reduce these. Unfortunately, oral medication is not always effective, can make the patient drowsy or lose it's effectiveness over time. Some patients elect to use an implant which can deliver precise amounts of medication to manage the spasms.

An FES Cycling intervention can help a majority of persons to damp down their leg spasms. Sometimes these get worse initially as the legs get stronger. In these cases the stimulation parameters can be fine tuned to help. Also stretching, and leg massage prior to a session can help.

Conclusion

Functional electrical stimulation in general and FES Cycling in particular is a safe and widely used modality with a good evidence base for supporting long term health. Many clients use these products at home for that reason. We would always encourage exploring the various options and thinking carefully about the possibilities. The technology available from ourselves and other suppliers will fundamentally attempt to do similar things but with differences in the user interface.