Functional Electrical Stimulation for Spasticity and Foot Drop: Who May Benefit?

Functional electrical stimulation, usually shortened to FES, can help some people lift the front of the foot at the right moment during walking. It is often discussed when foot drop follows a condition affecting the brain or spinal cord, such as stroke, multiple sclerosis, cerebral palsy, traumatic brain injury or an incomplete spinal cord injury. FES is not a general cure for spasticity, and it is not suitable for every cause of a catching toe or difficult gait.

This guide explains what a foot-drop FES system does, how it differs from neuromuscular electrical stimulation (NMES), who may be offered a trial, what an assessment involves and where its limitations lie. The most useful question is not simply whether a device can make the foot move in a clinic. It is whether that movement improves a goal that matters to the person—such as fewer trips, easier community walking, less effort or greater confidence—without creating unacceptable discomfort or risk.

Key points

• FES uses small electrical pulses to activate a nerve or muscle at a useful moment in a task. For foot drop, stimulation is commonly timed to the swing phase of walking.
• A trial is most relevant when the foot can respond to stimulation and the person’s difficulty comes from an upper motor neuron condition rather than damage to the peripheral nerve supplying the muscle.
• Foot drop may reflect weakness, poor timing, spastic muscle activity, sensory loss, fatigue or fixed restriction. FES addresses only some of these contributors.
• FES and an ankle-foot orthosis are both established options. Neither is automatically better; comfort, gait response, goals, skin health, hand function, cost and daily practicality all matter.
• Fitting should be performed by a trained clinician, followed by practice, skin checks and outcome review. Do not copy another person’s settings or place electrodes by trial and error.

What is functional electrical stimulation?

Electrical stimulation delivers controlled pulses through electrodes on the skin, or less commonly through an implanted system. The pulses activate excitable nerve fibres and produce a muscle contraction. It becomes functional electrical stimulation when that contraction is coordinated with a practical activity. In a foot-drop system, a sensor, tilt detector or movement algorithm identifies when the leg is entering swing. The device then stimulates the common peroneal nerve or the muscles that lift and turn the foot outward. Stimulation stops or changes as the foot prepares to contact the ground.

The aim is to improve toe clearance and the position of the foot for the next step. The sensation is often described as tingling or tapping, followed by a visible movement. It should be strong enough to create a useful response but not unnecessarily painful. Electrode position, pulse width, intensity and timing are individual. A small change can alter whether the foot lifts cleanly, turns outward too far or feels uncomfortable.

Most foot-drop devices are worn on the upper calf and used while walking. Some services also use FES for cycling, upper-limb tasks or other movements, but those applications require different equipment and assessment. The discussion here focuses on surface FES for walking.

Why does foot drop happen, and where does spasticity fit?

Foot drop means that the ankle does not lift sufficiently during swing. The toes may catch, the forefoot may slap down after contact, or the person may compensate by lifting the knee higher, circling the leg or leaning the trunk. The visible pattern does not identify the cause. Weak ankle dorsiflexors and poorly timed activation are common. Calf or inward-turning muscle overactivity may pull against the desired movement. Reduced sensation, fatigue, pain and limited joint range can contribute as well.

Spasticity is a velocity-dependent increase in resistance after damage to upper motor neuron pathways. It may be only one part of a broader problem that includes weakness and loss of selective control. A person can have foot drop with little spasticity, or substantial calf spasticity without foot drop. The detailed guide to spastic gait and lower-limb patterns explains why a catching toe should not automatically be labelled “tightness.”

FES can assist a movement when the peripheral nerve and muscle can still respond. It does not lengthen a fixed contracture, repair a damaged peripheral nerve or correct every gait problem. If the ankle cannot reach a useful position even when moved slowly, or if the foot is pulled strongly inward, a clinician may need to address range, alignment, footwear, an orthosis or focal spasticity treatment before—or alongside—FES.

FES, NMES and TENS: what is the difference?

The device hardware can look similar, and terminology is not always used consistently. The defining feature of FES is the functional timing. NMES may still be valuable in rehabilitation, but a muscle contracting while sitting is not the same as a system coordinating foot clearance over thousands of steps. TENS is not designed to correct foot drop. A device should be selected for a stated clinical purpose, not because “electrical stimulation” sounds like one treatment.

Who may benefit from a foot-drop FES trial?

FES is most often considered for foot drop caused by a central neurological condition—damage within the brain or spinal cord—when the peripheral pathway to the target muscles remains able to respond. People after stroke and people with multiple sclerosis form much of the research base. Selected people with cerebral palsy, traumatic brain injury or incomplete spinal cord injury may also be assessed.

A reasonable candidate often has all or most of the following:

• a repeatable problem with toe clearance that affects walking safety, effort or participation;
• a visible and useful ankle response when the nerve is stimulated;
• enough passive ankle range for the foot to move toward a safer position;
• the ability to walk at least a short distance, with an aid if needed, because the device assists part of the gait cycle rather than creating independent walking by itself;
• skin that can tolerate electrodes and sensation or support sufficient to notice irritation;
• the ability to position the device and operate it, or reliable help from a caregiver;
• a goal that can be tested during a trial.

Suitability is less likely when foot drop arises from a severe peripheral nerve lesion, when no useful contraction can be produced, or when a fixed deformity prevents the foot reaching a functional position. Marked swelling, very fragile skin, poorly controlled pain, severe instability or an unaddressed fall risk may need attention first. Cognitive, visual or hand difficulties do not always rule out FES, but they affect whether setup and troubleshooting can be done safely.

FES is not only for people with high tone. In fact, the main treatment target is often weakness or poor timing of dorsiflexion. When plantarflexor or invertor overactivity is prominent, the team may combine FES with task-specific rehabilitation, stretching for comfort and range, orthotic management or a focal treatment. The plan should preserve any tone the person uses for stance or transfers.

What happens during an FES assessment?

Clarifying the goal and gait problem

The clinician asks when the toe catches, how far the person walks, whether falls or near-falls occur, what footwear and aid are used, and whether fatigue changes the pattern. A goal may be safer indoor walking, a longer community distance, fewer stumbles or easier clearance on uneven ground. Baseline measures may include walking speed, a timed walk, perceived effort, fall history and a patient-reported goal.

Examining movement and the neurological level

The assessment includes passive and active ankle range, strength, selective control, sensation, skin, swelling, pain, balance and the response to movement at different speeds. This helps distinguish dynamic muscle overactivity from fixed restriction. If you want to understand the tone measures used in this process, see how spasticity is measured.

The clinician also considers whether the lesion is central or peripheral. Surface FES relies on a functioning peripheral motor pathway. Foot drop after a fibular nerve injury, severe peripheral neuropathy or certain muscle disorders may not respond in the same way as foot drop after stroke or multiple sclerosis.

Testing the stimulation response

Electrodes are placed to find a movement that clears the toes without excessive inversion, eversion or knee disturbance. The intensity is increased gradually. The person then walks with the system while timing and output are adjusted. A promising movement on the treatment couch is not enough; the team must observe real steps, turns, speed changes and use with the person’s normal shoe and walking aid.

Comparing meaningful options

An FES trial may be compared with usual walking, an ankle-foot orthosis or both. An ankle-foot orthosis provides mechanical support without electrical stimulation and may be preferable when the ankle needs strong control, the response to stimulation is poor or the device routine is impractical. Some people use FES in one setting and an orthosis in another.

What benefits are realistic, and what are the limits?

When fitting is successful, FES can improve toe clearance and foot position during the steps in which it is active. Studies in stroke and multiple sclerosis suggest that some users walk faster or find walking easier; for post-stroke foot drop, FES and ankle-foot orthoses often produce broadly comparable functional improvements. Individual response varies, and an average trial result does not predict what one person will experience.

Two types of effect are sometimes discussed. An orthotic effect is the immediate difference while the device is switched on. A training or therapeutic effect would be an improvement that remains when the device is off after repeated use. The immediate effect is usually easier to demonstrate. Lasting carry-over is less certain and should not be promised.

FES does not cure the underlying neurological condition or guarantee that spasticity will decrease. It may not correct a stiff knee, poor hip control, balance loss or sensory ataxia. The stimulation itself can fatigue the activated muscle, and the overall device may add cognitive or practical burden. Benefits should therefore be reviewed against drawbacks such as setup time, skin irritation, discomfort, electrode cost, charging, clothing, reliability and access to follow-up.

Success is not limited to speed. Fewer trips, improved confidence, lower perceived effort, better outdoor participation or the ability to wear a preferred shoe may be more meaningful. Conversely, a technically improved ankle movement is not a success if walking becomes painful, slower, less stable or too complicated for daily life. This is why goal-based review matters.

Safety, skin care and precautions

FES should be prescribed and fitted within a clinical service. Device-specific instructions take priority because systems differ. Tell the clinician about implanted electronic devices, heart rhythm problems, epilepsy, pregnancy, cancer or infection near the stimulation site, a history of blood clots, reduced sensation, severe osteoporosis, recent surgery and any metalwork near the electrodes. These factors do not all lead to the same decision, but they require individual review rather than guesswork.

Do not place electrodes over broken, infected or severely irritated skin, the front or sides of the neck, the head, or across the chest. A foot-drop system has a defined lower-limb placement. Do not use it while driving, bathing, swimming or in another situation prohibited by the manufacturer. Switch it off before moving or replacing electrodes.

Check the skin before and after use. Mild, short-lived redness under an electrode can occur, but persistent redness, blistering, swelling, burning pain, a rash or broken skin requires stopping and contacting the service. Clean dry skin and correctly stored electrodes improve contact. Moving electrodes away from the fitted position can change both comfort and movement.

Seek urgent medical assessment for sudden new foot drop, new facial or arm weakness, speech difficulty, severe back pain with bladder or bowel change, rapidly worsening numbness, or a hot swollen painful leg. These are not problems to troubleshoot by increasing the stimulation.

Making FES workable in daily life

Most services build wear time gradually. Early sessions focus on accurate placement, safe intensity, walking practice and skin tolerance. Taking a photograph or using a washable placement mark may help, if the service recommends it. Wear the same type of shoe used during fitting until you understand how footwear changes the response.

Keep a brief record of where and how long the device was used, any trips or falls, comfort, skin changes and battery or electrode problems. This is more useful than turning the intensity up whenever walking feels difficult. Fatigue, infection, pain, heat, poor sleep or a full bladder can change spasticity and gait; the device may need review rather than more stimulation.

Follow-up should revisit the original goal, inspect the skin, check electrode position and reassess the whole gait pattern. Changes in strength, weight, swelling, medication, orthoses or neurological status can alter the fit. FES works best as one part of a broader plan that may include practice, strength, balance, footwear, an aid and environmental strategies.

Frequently asked questions

Does FES reduce spasticity?

It may alter muscle activity during a task and some people report easier movement, but foot-drop FES is primarily used to assist timed dorsiflexion. It should not be described as a guaranteed or permanent treatment for spasticity.

Is FES better than an ankle-foot orthosis?

Not universally. Research after stroke suggests that both can improve walking. Preference and benefit depend on the gait problem, response to stimulation, stability needs, comfort, skin, footwear, hand function, cost and daily routine. A structured trial is more informative than a general ranking.

Can I buy a stimulator and set it up myself?

A generic stimulator may not provide reliable gait-triggered timing, and incorrect electrode placement can create an unwanted movement or skin injury. Assessment, fitting and follow-up by a trained clinician are important, especially when spasticity, sensory loss or an implanted device is present.

Will FES make the muscles dependent on the device?

The device supplies an electrical trigger while it is on; it does not make the nervous system “lazy.” However, the improvement may be mainly an on-device effect. Continue the rehabilitation activities recommended for strength, balance and motor practice rather than treating FES as a complete programme.

How long does it take to know whether it helps?

A useful ankle response may be visible in the first assessment, but daily practicality, skin tolerance and meaningful walking benefit often require a trial and follow-up. The service should define what will be measured and when the decision will be reviewed.