What Is FES Cycling?

What You Will Learn

In this chapter, we explain what FES cycling is and how it works in straightforward terms. You will learn how electrical stimulation is used to produce active exercise in weak or paralysed muscles, how this differs from passive cycling and standard exercise bikes, what the experience actually feels like, and who can benefit from it. By the end, you should have a clear picture of what FES cycling involves before we explore the science and evidence in later chapters.

The Basic Idea: Electrical Stimulation Synchronised with Pedalling

FES cycling combines two pieces of equipment, as shown in Figure 1 below: a programmable electrical stimulator (delivering functional electrical stimulation, or FES) and a cycle ergometer (an exercise bike designed for rehabilitation, sometimes called a passive/active bike). In the traditional implementation of FES cycling, these two systems would be connected via a communication cable, allowing information to be passed between them. As we will see later, this means that only certain combinations of bike and stimulator were available.

The RehaMove system (now obsolete) utilised the RehaMove 8-channel stimulator with various Motomed bike models. The system was controlled by the stimulator, which monitored the instantaneous position of the bike pedals and used that information to determine which muscle to stimulate at that time. Beyond this, the intensity of stimulation could be automatically varied based on the user's pedalling performance.

The Stim2go FES system, which we're now working with, frees up the limitation to rely on specific models of bikes. You still have a stimulator and a bike, but there's no need for a cable connection between them. Sensors within the stimulator allow the stimulation to synchronise muscle contractions with the user's leg movements. This allows any passive or active bike model to be used in creating an FES cycling system. More about all that later.

The user will normally access the bike from a wheelchair. The stimulator delivers small, controlled electrical pulses to the major leg muscles through surface electrodes, and then the system is designed to allow the right muscles to fire at the right moment to produce a smooth pedalling action.

In other words, the stimulator is doing the job that your brain and spinal cord would normally do. When you pedal a bike voluntarily, your brain sends signals down the spinal cord and along the peripheral nerves to tell your leg muscles when to contract and when to relax. In conditions such as spinal cord injury or stroke, that pathway is disrupted. The stimulator provides an alternative route, delivering the signals directly to the muscles through the skin.

The critical point is this: FES cycling is active exercise.

When set up correctly, your muscles genuinely contract and do useful work, even if you have no voluntary control over them. This is what makes FES cycling fundamentally different from simply having your legs moved by a machine. When muscles contract actively, they consume energy, demand oxygen, and adapt over time by getting stronger. This enhances cardiovascular and metabolic health. This is the foundation of the health benefits that we will explore in Chapter 4.

A typical FES cycling system will have multiple channels to stimulate different muscle groups. All products would stimulate at least the quadriceps (the muscles at the front of the thigh) and the hamstrings (the muscles at the back of the thigh). Many systems also stimulate the gluteal muscles (the buttocks) and, depending on the programme's goals, sometimes the calf muscles (gastrocnemius/soleus) and those at the front of the lower leg (tibialis anterior).

As we described above, the stimulator continuously monitors pedal position and uses this information to adjust which muscles are stimulated and when. The knowledge of how to do this is typically stored in a programme within the stimulator. Some systems can automatically vary the nature of the stimulation to control the cycling speed, the pedalling resistance, and more. By adjusting the stimulator's settings, the user's muscles can become stronger and do more work over time.

Although we have just described FES cycling with a user sitting in a wheelchair and exercising their legs, there are some variations. For example, some bikes support arm-cranking exercise with FES applied to the upper limbs and shoulders; some variations involve FES cycling whilst lying in bed (Fig 3), and some versions support outdoor biking.

How FES Cycling Differs from Passive Cycling and Standard Exercise Bikes

It is worth clarifying how FES cycling compares with other cycling options you may have encountered.

A standard indoor exercise bike relies entirely on voluntary muscle control. If you can consciously contract your leg muscles, you can pedal. For many people with neurological conditions, this is not possible for some or all of the muscles in their legs due to the resulting weakness or paralysis.

A passive/active cycling bike, such as those from MOTOmed or THERA-Trainer, can use an electric motor to move your legs through a pedalling motion. The user can choose different speeds and resistance levels, which is very useful if they have some ability to pedal on their own. These bikes can allow the user to pedal themselves if possible, but will automatically take over and move the user's legs passively if fatigue sets in. They will have features to support leg positioning and may well have games to encourage usage.

Products such as the MOTOmed and THERA-Trainer ranges are widely used in hospitals and homes. Passive cycling does have value: it helps maintain joint range of motion, provides temporary relief from spasticity, and reduces oedema. The only things that would limit someone from using this type of bike are a limited range of motion at the knees or hips, or pain when moving through that range. However, because the muscles are not actively contracting, it does not build muscle mass, improve cardiovascular fitness, or produce the metabolic benefits associated with genuine exercise.

FES cycling adds the vital element that passive cycling lacks: active muscle contraction. Research over decades has consistently shown that FES cycling produces benefits that passive cycling alone does not. We cover this evidence in detail in Chapter 4.

The following table summarises the key differences:

What the Experience Feels Like

One of the questions people ask is: what does FES actually feel like?

The answer depends on the user's condition and level of sensation. Many of our clients have spinal cord injuries where they have no, or altered, feeling in the areas where the electrodes are placed. For these individuals, the stimulation itself is not felt. You may see your muscles contracting and your legs moving, but there is no accompanying sensation. This can seem unusual at first, but most people quickly become accustomed to it.

If you have some preserved sensation, as is common with incomplete spinal cord injuries, stroke, or multiple sclerosis, you will typically feel a tingling or pulsing sensation beneath the electrodes when the stimulation is active. The intensity is always adjustable, and your clinician will work with you to find a level that produces a good muscle contraction without discomfort. The vast majority of people tolerate FES well. Occasionally, someone will find the sensation difficult to get used to at higher intensities, but this is quite unusual.

What you are likely to notice most in your first session is how quickly your muscles tire. Muscles that have not been used actively for weeks or months will fatigue rapidly, and it is entirely normal for a first session to last only fifteen to twenty minutes. This is not a failure of the process; it is a starting point. Over the coming weeks, your muscles will adapt, sessions will get longer, and the power you generate will increase. Think of it more as a marathon than a sprint. After a spinal cord injury muscle fibre types change in a way that makes them more fatigable and it will take time for you physiology to adapt. As with all forms of exercise with humans, you need to exercise regularly and gradually introduce adaptations to make progress toward any fitness goals.

If you have a spinal cord injury above the T6 level, your clinical team will monitor you carefully at first for a condition called autonomic dysreflexia, which provokes a sudden spike in blood pressure. Most people at risk of this will already be familiar with it from their rehabilitation. We cover this topic fully in Chapter 9.

A Brief Visual Walkthrough of a Typical FES Cycling Session

To help you picture what a session involves, here is a step-by-step walkthrough of what typically happens. Let's just assume it's leg cycling we're going for. The very first time, the clinician working with you would want to establish that it's safe for you to use FES cycling. Every medical device has contraindications that exclude certain people from using it. These products are no different. It's sensible for users to become familiar with these contraindications in case anything changes over time that might prevent them from using a bike.

Before the session. You transfer into position at the bike, either from your wheelchair or from a bed, depending on the system type. Your feet are secured to the pedals using straps or adapted footplates. Finding the right position at first takes a bit of exploration. You want to move your legs through a good range of motion, but not have the legs fully extended at any time. It is a good idea to ensure your bowel and bladder are managed before you begin.

Electrode placement. Your clinician, carer, or you yourself (once trained) place a pair of adhesive electrode pads on the skin over each of the muscle groups that will be stimulated. Correct placement of electrodes matters, but is not critical. Consistency of placement from session to session is more important, and you will be shown where the electrodes should go.

System setup. The stimulator is switched on, and the stimulation parameters are set. Your clinician will check the intensity for each muscle group individually, looking for a strong contraction without discomfort. This process takes a few minutes, especially in early sessions.

Warm-up. The bike motor begins moving your legs passively at a gentle speed. The stimulation is then gradually introduced, and you will see your muscles begin to contribute to pedalling. We aim to make the transition from passive to active cycling as smooth as possible. If a client has leg spasms, these can make the cycling action jerky, and in these cases, we would expect to move the legs passively for a few minutes until this settles down. A lower stimulation intensity can be included at this stage if it helps the muscles relax slightly.

Active cycling. Once the stimulation is engaged, the aim is for you to cycle actively against a set amount of resistance. The system might monitor your pedal speed and the power you are generating. You may see this information displayed on a screen. Your clinician may adjust the resistance, cycling speed or stimulation intensity during the session depending on how your muscles are responding.

Cool down and finish. Towards the end of the session, the stimulation intensity is reduced, and the bike returns to passive mode for a brief cool-down. The electrodes are then removed, and your skin is checked. The whole process, including setup and removal, typically takes around 30 to 45 minutes, with the active cycling portion sometimes shorter, especially in the early weeks.

Who Can Benefit from FES Cycling

As noted above, FES cycling is used by people with a range of neurological conditions. The strongest evidence base is in spinal cord injury, where it has been studied extensively. However, it can also be used effectively for stroke, multiple sclerosis, Parkinson's disease, cerebral palsy, and other conditions that result in lower limb weakness or paralysis.

Each condition has its own considerations. The response to FES cycling varies depending on the nature and severity of the neurological impairment, the time since the injury or diagnosis, and the individual's overall health. We explore the evidence for each condition in detail in Chapter 5.

As mentioned above, there are situations in which FES cycling may not be appropriate. Contraindications include certain cardiac conditions, active fractures in the limbs being exercised, severe joint contractures that prevent a pedalling motion, pregnancy, and the presence of certain implanted medical devices. A thorough clinical assessment before you begin will identify any contraindications. Providers of these products will always state the contraindications for their particular product. We cover these in Chapter 6.

As we mentioned in the foreword, FES cycling requires that the so-called lower motor neurons (the nerves that run from the spinal cord to the muscles) be intact. Where these nerves are damaged, the muscles cannot respond to standard electrical stimulation, and a different approach is needed. If you are unsure whether this applies to you, a clinical assessment that includes testing your muscles' response to stimulation will provide the answer.

Chapter Summary

• FES cycling combines a programmable electrical stimulator with a cycle ergometer to produce active exercise in weak or paralysed muscles.
• The stimulation is synchronised with pedal rotation so that the right muscles contract at the right time, producing a coordinated pedalling action.
• Unlike passive cycling, FES cycling induces genuine muscle contraction, which underpins its health benefits: building muscle, improving cardiovascular fitness, increasing bone density, and reducing spasticity.
• The experience varies depending on your level of sensation, but most people tolerate FES well. Muscles fatigue quickly at first, and this is normal.
• FES cycling is used for spinal cord injury, stroke, multiple sclerosis, Parkinson's disease, cerebral palsy, and other neurological conditions, though a clinical assessment is essential to confirm suitability.

In Chapter 2, we look at how your muscles and nerves work, and why that understanding matters for getting the most from FES cycling.