Combining tSCS with FES Cycling. What's the benefit?
Functional electrical stimulation (FES) Cycling is a well-researched modality with long-term benefits for those recovering from a spinal cord injury. Users can actively exercise the large muscles of the legs despite paralysis.[1][2]. Although there are some contraindications, it is a safe and effective technique for many and is used by hundreds of our clients who use these systems at home. After some 18 years of experience in the UK, we still find that this is a well-accepted and popular technique, with adoption primarily limited by the cost of the systems.
With the introduction of the new Stim2Go stimulator from Pajunk at the core of our UK FES bike offering, we’re unlocking exciting new possibilities thanks to its innovative and promising features.
In other articles, we have commented on particular features and benefits of the Stim2Go, including its ability to turn any passive-active bike into an FES cycling system. The Stim2Go is equipped with sensors which allow stimulation to be triggered by movement.
In this article, we're primarily focusing on applying tSCS within Stim2Go.
What is tSCS and why should I care
Transcutaneous spinal cord stimulation (tSCS) is a technology that offers a non-invasive approach to treating various neurological conditions. It's a non-invasive technique that delivers electrical current to the spinal cord through electrodes placed on the skin overlying the spine. This stimulation activates neural circuits in the spinal cord, potentially improving various functions impaired by injury or disease. The exact placement of electrodes depends on which functions are being targeted—cervical stimulation for upper limb function, thoracic for trunk control, or lumbar for lower limb applications.
Unlike implanted spinal cord stimulators that require surgery, tSCS operates externally, offering a safer, non-invasive alternative for individuals. This approach not only reduces risks but also improves accessibility. tSCS can target specific spinal cord segments based on the desired therapeutic outcome, providing tailored treatment options. Additionally, it is more cost-effective than surgical solutions and can be discontinued immediately if any adverse effects arise, ensuring greater flexibility and patient safety.
The main applications are for managing pain, spasticity, and potentially encouraging functional improvements, especially when used alongside other therapy interventions.
As we have written about in other articles, the field has a long history. I believe the first articles about tSCS were written around 1996. Still, interest has expanded rapidly in the past decade as researchers discovered that tSCS could not only reduce spasticity and pain but also potentially improve voluntary movement in people with spinal cord injuries.
As we will see below, tSCS is not 'one thing' any more than electrical stimulation is one thing. Different paradigms are being applied, and we still have much to learn about how stimulation parameters and electrode placements influence outcomes. Let's take a look at how tSCS is implemented in the Stim2Go.
What did tSCS ever do for us!
tSCS and Stim2Go
There are four programme templates that aim to deploy tSCS within Stim2Go. These are:-
tSCS Priming
Lower Frequency treatment (33 Hz) for moderate spasticity management
Higher Frequency treatment (50 Hz) for more severe spasticity management.
tSCS combined with FES Cycling
The tSCS programs are specifically designed for spasticity reduction, particularly with spinal cord injury or multiple sclerosis in mind. The treatment requires a special electrode configuration with three electrodes: two placed on the abdomen and one at the T11-T12 vertebrae.
I should comment here that the tSCS programs are MDR approved in Europe only and are not FDA cleared. Currently, no functional claims are being made for this tSCS application.
Technical Flavours of tSCS
There is a lot of interest in tSCS, and as we point out above, not all implementations of this idea are technically the same.
The 'conventional' waveform used for tSCS is a rectangular form of pulse with a duration of 1–2 ms applied at 30–50 Hz to facilitate muscle activation. An alternative approach uses a high-frequency carrier wave, typically 10 kHz, within the 1–2 ms pulse.
The use of a high-frequency carrier, commonly known as "Russian current," supposedly originated in Russia during the 1970s. The benefit of the high-frequency carrier, originally selected to be 2.5 kHz, was that it made the stimulation less painful. A later study found the optimal frequency for motor activation and minimal pain to be 10 kHz. Several tSCS studies claim that stimulation at 10 kHz is painless due to blocking of superficial nociceptive afferents, enabling the use of higher stimulation amplitudes, such as those needed to target the spinal roots.
The ARCex system from Onward Medical has attracted attention due to positive clinical trial results. This system uses a 10 kHz carrier frequency with a 1 ms pulse width for its stimulation waveform. According to the company, this configuration is integral to its design for technical and functional reasons.
The approach uses a high-frequency carrier (10 kHz) signal to enable efficient current delivery to spinal circuits while minimising skin impedance and discomfort. It aims to bypass activation of small-diameter pain fibres (Aδ/C fibres), which respond to lower frequencies (<1 kHz), allowing therapeutic currents to target large-diameter sensory fibres.
The carrier frequency should reduce capacitive effects at the skin-electrode interface, improving stimulation precision. If true, it should require lower stimulation intensities compared to non-carrier-based approaches. While carrier frequencies are not universally required to implement tSCS, they are intended to balance efficacy, comfort, and safety within Onward's specific implementation.
Alternative systems (e.g., biphasic pulses) exist, but if the logic of using a carrier is correct, they may trade off higher discomfort for equivalent therapeutic effects.
Ashley N Dalrymple [6], in the 2023 article, states that using a high-frequency carrier does not improve the comfort of tSCS.
On the issue of function, modern stimulators are typically current-controlled and automatically adjust their output to ensure the preset current is delivered, potentially obviating the need for carrier frequencies, as they ensure electrical losses in the skin do not affect the delivered current
The Stim2Go approach does not utilise a carrier frequency. Does this mean it will be less comfortable and practical compared with the Onward Medical approach? We don't have the answer yet, but we will be keen to monitor outcomes as we deploy the Stim2Go in the UK.
tSCS Priming programme
We know that the stimulation parameters and the positioning of electrodes will influence the effectiveness of tSCS. The tSCS priming program within Stim2Go determines the required stimulation intensity for the three other tSCS programs.
The stimulation pattern is biphasic, rectangular, with a frequency of 1 Hz. Stimulation should preferably be carried out in a supine or standing position. (for example, in a standing frame). Three electrodes are required. Two electrodes are placed on the abdomen and connected with an adapter cable before connecting to the cathode of the Stim2Go channel. The electrode on the back is placed on the spine at the level of T11-T12 and connected to the anode of the same channel.
The current intensity should then be increased slowly until muscle twitches can be seen in the legs (evoking a PRM or posterior root-muscle reflex). We would then use 90% of this to determine the current intensity to be used in the other three tSCS programs.
Lower and higher frequency applications
The two tSCS programs for spasticity reduction utilise biphasic rectangular pulses with a maximum pulse width of 1000 microseconds. For moderate spasticity, the 33 Hz program is used. For higher levels of spasticity, the 50 Hz program is used. The current level determined in the priming program guides the stimulation intensity.
Spasticity—characterised by tight, stiff muscles and exaggerated reflexes—can be significantly improved with tSCS:
A single 30-minute session of tSCS can produce immediate reductions in spasticity measurements
Benefits may last up to 2 hours after treatment
Multiple benefits have been documented, including reduced Modified Ashworth Scale scores (a measure of spasticity), decreased clonus (rhythmic muscle contractions), and fewer spasms
With regular application over 6 weeks, progressive improvements and carry-over effects lasting up to 7 days have been observed
This makes tSCS a promising non-pharmacological alternative to medications that often come with side effects.
Spasticity management with tSCS
tSCS Combined with FES Cycling
Applying FES Cycling combined with lumbar transcutaneous spinal cord stimulation (tSCS) may offer synergistic benefits for spinal cord injury (SCI) rehabilitation by enhancing neuroplasticity and functional recovery. Here's how this combination might create value:
Enhanced Neuroplasticity Through Spinal Circuit Priming
tSCS applied to the lumbosacral region is intended to increase spinal circuit excitability, enabling the nervous system to utilise preserved neural pathways more effectively. When paired with FES Cycling, which provides repetitive, task-specific muscle activation, this creates a "primed" environment for activity-dependent neuroplasticity. Studies show that such combined approaches improve voluntary movement potential in incomplete SCI cases by reinforcing descending motor commands[6].
'Optimised' FES Cycling
While FES cycling alone reduces spasticity through muscle activation[1][3], adding tSCS may amplify and prolong these effects:
Case studies using tSCS during swimming reported 4+ hours of post-session spasticity reduction[7]
Meta-analyses demonstrate FES cycling reduces Ashworth Scale scores by 0.5-1.0 points[3]
Combined modalities likely work through complementary mechanisms: FES modulates peripheral muscle tone while tSCS inhibits hyperactive spinal reflexes[3][6]
Optimised Motor Output During Cycling
tSCS enhances locomotor pattern generation in the lumbosacral cord[6], which may:
Reduce FES stimulation requirements by 15-30% through central contribution
Improve pedalling coordination via interlimb reflex modulation
Increase power output (studies show FES cycling alone boosts peak power by 35%[1])
Long-Term Physiological Benefits
The combination addresses multiple SCI complications simultaneously:
For muscle atrophy prevention, we know that FES Cycling can lead to greater quadriceps mass[1] and tSCS should enhance the neural drive to muscles.
FES Cycling assists bone density preservation by increasing the mechanical loading, as tSCS may improve osteogenic signalling.
FES Cycling can contribute to cardiovascular health though VO₂ max and blood pressure improvement [2], with tSCS contributing sympathetic modulation[5]
Personalised Rehabilitation Potential
The lumbosacral focus of tSCS aligns with cycling biomechanics, allowing targeted intervention for:
T6-T12 injuries: Maximises preserved trunk control
Incomplete injuries: Exploits residual supraspinal connections
Chronic SCI: Overcomes diminished spinal excitability[1][5]
Clinical Implementation Considerations
Optimal parameters: 30Hz tSCS during active cycling sessions[6]
Session structure: 45-60 minutes, 3x/week (matches FES cycling protocols)
Safety: Both modalities show low adverse event risk in trials[2][3]
This combined approach represents a paradigm shift in SCI rehabilitation. While more research is needed on long-term outcomes, early evidence suggests additive benefits for motor recovery and quality of life.
How long would it take for the benefits of FES Cycling combined with tSCS to be effective?
As described above, the expected short-term benefits are for pain or spasticity management, and no claims can be made for functional gains.
However, when combining lumbar tSCS with FES Cycling, we believe any functional changes would be slower to reveal themselves. Certainly, we expect in practice to focus on establishing tolerance via the tSCS priming programme and refining the technique rather than expecting significant changes.
Conclusion
The integration of tSCS within the Stim2Go platform presents a promising tool for managing pain and spasticity while supporting long-term rehabilitation strategies. Although immediate functional gains may not be anticipated, the combination of tSCS with FES Cycling allows users to gradually explore this exercise in a new and promising way. This emphasis on a patient-centred and progressive approach ensures that the implementation of tSCS aligns with the platform’s goal of delivering innovative and supportive neuromodulation solutions.
References
[1] Sadowsky CL, Hammond ER, Strohl AB, Commean PK, Eby SA, Damiano DL, Wingert JR, Bae KT, McDonald JW 3rd. Lower extremity functional electrical stimulation cycling promotes physical and functional recovery in chronic spinal cord injury. J Spinal Cord Med. 2013 Nov;36(6):623-31. doi: 10.1179/2045772313Y.0000000101. Epub 2013 Mar 20. PMID: 24094120; PMCID: PMC3831323.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3831323/
[2] van der Scheer JW, Goosey-Tolfrey VL, Valentino SE, Davis GM, Ho CH. Functional electrical stimulation cycling exercise after spinal cord injury: a systematic review of health and fitness-related outcomes. J Neuroeng Rehabil. 2021 Jun 12;18(1):99. doi: 10.1186/s12984-021-00882-8. PMID: 34118958; PMCID: PMC8196442.
https://pmc.ncbi.nlm.nih.gov/articles/PMC8196442/
[3] Massey Sarah , Vanhoestenberghe Anne , Duffell Lynsey. Neurophysiological and clinical outcome measures of the impact of electrical stimulation on spasticity in spinal cord injury: Systematic review and meta-analysis. Frontiers in Rehabilitation Sciences, Volume 3 - 2022. doi=10.3389/fresc.2022.1058663. ISSN=2673-686. https://www.frontiersin.org/journals/rehabilitation-sciences/articles/10.3389/fresc.2022.1058663/full
[4] Functional Electrical Stimulation Cycling for Spinal Cord Injury https://www.physio-pedia.com/Functional_Electrical_Stimulation_Cycling_for_Spinal_Cord_Injury
[5] An Introduction to Transcutaneous Spinal Cord Stimulation https://www.anatomicalconcepts.com/articles/introduction-to-transcutaneous-spinal-cord-stimulation
[6] Ashley N Dalrymple et al 2023. Using a high-frequency carrier does not improve comfort of transcutaneous spinal cord stimulation. J. Neural Eng. 20 (2023) 016016 https://doi.org/10.1088/1741-2552/acabe8
[7] Electrical Stimulation in Water - Project STIMSWIM. https://www.sensorstim.de