(Vienna, 12 May 2026) – A new study involving the Medical University of Vienna shows that, in transcutaneous spinal cord stimulation, the choice of current waveform is crucial for the therapeutic effect. The findings, published in Nature Biomedical Engineering, suggest that currently popular high-frequency waveforms do not improve treatment success, but may even be counterproductive under certain conditions.
Non-invasive electrical stimulation of the spinal cord has emerged as an important field of research with growing clinical relevance for neurorehabilitation following spinal cord injury. International studies have shown that some patients regained the ablity to walk, even after severe and long-standing injuries. A common feature of these studies was the use of implantable systems to modulate neuronal networks in the spinal cord, which enabled active participation in intensive rehabilitation programmes. In recent years, transcutaneous spinal cord stimulation using adhesive skin electrodes—a method pioneered by the Viennese co-authors of the current study—has increasingly established itself as a viable non-invasive alternative backed by clinical evidence. Lately, the use of specific high-frequency waveforms within this field has seen a rapid increase in interest. These waveforms were originally designed for peripheral muscle stimulation to maximise contractions while minimising discomfort. They were adopted for neuromodulatory applications due to their supposedly superior tolerability even though their underlying mechanisms remained insufficiently understood. An international research team from Washington University School of Medicine, Friedrich-Alexander University Erlangen-Nuremberg and the Medical University of Vienna (led by Ursula Hofstötter and Karen Minassian from the Centre for Medical Physics and Biomedical Engineering) has now systematically investigated this approach.
High-frequency pulses increase stimulation thresholds
In a comprehensive study involving 28 participants and supplementary computional models, the team demonstrated that high-frequency pulse shapes hinder the generation of nerve impulses. This raises the stimulation thresholds, effectively negating the benefit of improved tolerability, as higher current intensities are required to achieve therapeutic effects.
A major discovery concerns the type of nerve fibres activated. Effective neuromodulation requires the activation of proprioceptive afferent fibres, i.e., the pathways that transmit signals towards the spinal cord. However, high-frequency pulses preferentially stimulate motor fibres, which carry signals away from the spinal cord. Consequently, the target neural structures within the spinal cord are largely bypassed.
New findings on stimulation of the cervical spinal cord
Whilst previous research has focused primarily on the lumbar spinal cord, which is essential for leg movements, the cervical spinal cord has recently gained attention for its potential in restoring hand and arm function. However, the current study reveals a critical distinction: in the cervical spinal cord region, motor fibres are preferentially activated regardless of the selected pulse shape. This challenges the previous assumption that methods used to modulate lumbar spinal networks are directly transferable to the cervical region.
Relevance for clinical practice
The results provide a founadtaional mechanistic framework for the development of future therapies. They show that high-frequency pulse shapes are not a universally superior approach and underscore the need for a rigorous electrophysiological understanding before their clinical implementation in the cervical spine. At the same time, the study suggests that new, high-cost devices utilising high-frequency pulse shapes offer no therapeutic advantage over conventional, more affordable systems.
Publication: Nature Biomedical Engineering
Fundamental limitations of kilohertz-frequency carriers in afferent fibre recruitment with transcutaneous spinal cord stimulation
Rodolfo Keesey, Ursula Hofstoetter, Zhaoshun Hu, Lorenzo Lombardi, Rachel Hawthorn, Noah Bryson, Abdallah Alashqar, Andreas Rowald, Karen Minassian, Ismael Seáñez
DOI: 10.1038/s41551-026-01684-w