A question I am asked regularly, usually by someone with an injury at or above T6 who has just started researching FES cycling, goes something like this: "I have read that FES can trigger autonomic dysreflexia. Does that mean it is not for me?"

It is a fair question, and I do not want to brush past it. Autonomic dysreflexia (AD) is genuinely serious, and anyone with a high-level injury has good reason to take it seriously before plugging themselves into a stimulator. But the honest answer is not a simple yes or no. With the right assessment, the right setup, and the right monitoring, most people with a higher-level injury can use FES cycling safely. The problems almost always come from programmes that were never properly set up in the first place.

Here is what you need to know before you start.

A Quick Refresher on Autonomic Dysreflexia

AD is a sudden, exaggerated response of the autonomic nervous system to a (noxious) trigger below the level of injury. The classic picture is a pounding headache, a flushed or sweaty face above the lesion, goosebumps, a blocked nose, and, crucially, a sharp rise in blood pressure. Below the level of the lesion, you often see the opposite: cold, pale, clammy skin.

The reason it happens is a loss of 'top-down' control. The autonomic nervous system is often viewed as having two sides: the sympathetic and parasympathetic. The sympathetic nervous system, sometimes referred to as the fight-or-flight response, and the parasympathetic nervous system help restore balance. An irritating stimulus below the injury (a full bladder, a kinked catheter, a pressure sore, or, yes, strong muscle contractions) can trigger a sympathetic reflex. In the absence of a spinal cord injury, the brain dampens that reflex. After a high-level spinal cord injury, it cannot, and blood pressure climbs unchecked.

AD is classically associated with injuries at T6 and above, although cases are reported lower. It is not rare. The SCIRE Project's 2025 review is a good starting point for anyone who wants to go deeper than this article.

KEY POINT: AD is a medical emergency when it is severe. Untreated, it can cause strokes, seizures, and, in rare cases, death.

Why FES Cycling Can Set It Off, and How Often It Actually Does

FES cycling can produce strong, repeated muscle contractions in the legs. For someone whose autonomic control is intact, that is just exercise. For someone with a high cervical or upper thoracic injury, those contractions can act as the noxious stimulus that sets off an AD reflex.

Two things are worth saying here.

First, the research distinguishes between symptomatic AD (where the person feels the headache, flushing, and blood pressure rise) and silent AD (where blood pressure rises significantly but the person feels nothing). Recent work on spinal stimulation in people with SCI has found that a meaningful proportion of stimulation sessions produce AD events, and the striking finding is that the overwhelming majority of those events are silent. You can have a 40 mmHg jump in systolic pressure and feel nothing at all.

Second, silent AD is not harmless. Repeated, undetected blood pressure spikes place a long-term load on an already vulnerable cardiovascular system. That is one of the reasons a proper assessment of a new FES cycling user might include a resting blood pressure baseline and, for higher-level injuries, a way of checking pressure during the first sessions at home.

In my experience, working with FES Cycling for around 20 years, the clients who get into trouble are almost never the ones who understood the risk from the start.

Red Flags Before You Start

Before anyone with a T6 or higher injury starts an FES cycling programme, there are situations that genuinely do warrant caution, and a few that should stop you from starting until they are sorted out.

Things that should be properly managed first:

A history of recurrent or uncontrolled AD episodes
An ongoing urinary tract infection, or unreliable bladder or bowel management
An active pressure ulcer or broken skin in the stimulation area
Uncontrolled or poorly monitored resting blood pressure
Significant cardiac problems that have not been reviewed recently

Things that need clinician's sign-off but are rarely outright blockers:

A history of AD that is now well controlled
Ingrown toenails, minor skin issues, or tight clothing habits (easy to fix, but genuinely common triggers)
Anticoagulant therapy or a history of thromboembolism (case by case)

The fact is that most of these are practical issues, not philosophical ones. Sort them out first, and you remove the triggers before you ever add the stimulator to the picture.

How a Properly Set Up Programme Reduces the Risk

This is the part of the conversation that often gets skipped, and it is the part that matters most. An FES cycling programme can deliberately do several things to reduce AD risk.

Pre-session checks. Every session starts with the same quick checklist: bladder emptied, bowel management done, skin checked, clothing loose, baseline resting blood pressure noted. It takes two minutes, and it removes most of the avoidable triggers.

Gradual current ramping. Modern stimulators, including the Stim2Go, ramp current up slowly rather than switching on at full intensity. That smoother build is far less likely to provoke a reflex response than a sudden, strong contraction.

Short starter sessions. We often recommend that the first two weeks of a new programme are deliberately undercooked: shorter sessions, lower intensity, conservative cadence. You are not trying to get a training effect yet. You are learning how your body responds. We will say 'its a marathon - not a sprint'. It's Important to let your body adjust to the demands of this exercise.

Home blood pressure monitoring. For higher-level injuries, a home BP cuff can be used during the first few weeks, with readings taken before, during, and after each session. This is the single most effective way to catch silent AD early. It does not need to be complicated. A simple upper-arm cuff and a written log will do.

A session diary. Record the session settings, any symptoms, BP readings, and anything unusual. Over the first month, patterns emerge that tell you exactly where your personal threshold sits.

Done properly, these steps turn FES cycling from "potentially risky for my injury level" into "a programme my clinician is comfortable signing off on."

What to Do If AD Happens During a Session

Even with a careful setup, you may still get the occasional symptomatic episode. If that happens:

Stop the stimulation immediately.
Sit fully upright if you can, or raise the head of the bed. Gravity helps bring blood pressure down.
Loosen anything tight: abdominal binder, shoes, waistband, leg straps.
Look for the obvious triggers: full bladder, blocked catheter, tight clothing, pressure on the skin.
Check your blood pressure if you have a cuff to hand.
If symptoms do not settle within a few minutes or if blood pressure stays high, contact your spinal unit or call 999. AD is one of the situations where ambulance crews genuinely want to hear from you early, not late.

Keep a written AD action plan where you can see it during sessions. If you live with someone, make sure they know the plan too.

Working with Your Clinician and Case Manager

One pattern we have seen in the past is that a cautious clinician will sometimes flag AD as a reason to decline FES cycling altogether. That is understandable, but it is rarely the right answer. The right answer is a proper assessment.

If you are in that position, it helps to bring evidence to the conversation: the SCIRE Project's AD review, the Physiopedia summary of FES cycling risks and dosing, and recent data on silent AD during spinal stimulation (for example, Squair and colleagues, 2024). Share the monitoring plan. Share the session diary template. Give your clinician the tools to say yes safely, rather than forcing them to say no on a general principle.

In our experience, clinicians who start off sceptical become supportive very quickly once they see a structured plan with baseline BP data, clear stopping rules, and a documented response protocol.

Where to Go From Here

If this topic is relevant to you, the next practical step is not to buy equipment. It is to get a proper pre-purchase assessment. AD risk is not a reason to rule yourself out. It is a reason to insist on a careful assessment before anyone takes your money, so that whatever system you end up with is one you can actually use safely and consistently over the long term.

If you would like to talk through your situation, or you would like a copy of the assessment and monitoring template I use with new FES cycling clients, please get in touch. The FES Cycling patient guide on this site covers the wider programme in more depth, and the chatbot is there if you have follow-up questions you would rather not ask a human first.

Autonomic Dysreflexia and FES Cycling: What Higher-Level Tetraplegics Need to Know Before Starting

A Quick Refresher on Autonomic Dysreflexia

Why FES Cycling Can Set It Off, and How Often It Actually Does

Red Flags Before You Start

How a Properly Set Up Programme Reduces the Risk

What to Do If AD Happens During a Session

Working with Your Clinician and Case Manager

Where to Go From Here

Further Reading

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