Advancing neuromuscular electrical stimulation optimizing comfort and hemodynamic efficiency

Physical inactivity and immobilization are significant contributors to global health challenges, including venous thromboembolism (VTE), muscle atrophy, and chronic diseases. Neuromuscular electrical stimulation (NMES) has emerged as a promising intervention to counteract these effects by mimicking muscle contractions and enhancing venous circulation. However, traditional NMES systems face barriers such as discomfort, complex setups, and poor compliance.

This thesis explores innovative approaches to improve NMES comfort and efficiency by integrating textile electrodes into wearable garments, such as socks, and optimizing stimulation parameters. The research comprised five interrelated studies investigating the design, efficacy, and usability of textile- based NMES systems.

Study I examined the construction of textile electrodes, focusing on how hydration and pressure affected stimulation performance. Results demonstrated that hydrated electrodes under moderate compression (~20 mmHg) significantly improved comfort and reduced both current intensity requirements and performance variability for effective muscle activation.

Study II mapped motor points on the calf muscles to identify areas optimal for electrode placement. A probability heatmap was developed to guide electrode positioning, thereby enhancing stimulation precision without requiring professional assistance.

Study III compared newly developed transverse textile electrodes integrated into socks (TTE-socks) with standard gel electrodes placed on motor points (MPE) at different intensity levels. Both configurations effectively increased venous hemodynamics in key veins, such as the popliteal and femoral veins, compared to baseline. However, in most of the comparisons, NMES via TTE- socks produced significantly greater hemodynamic responses, though it required slightly higher current and caused marginally more discomfort.

Study IV optimized NMES parameter settings for the TTE-sock by testing combinations of frequency (1 or 36 Hz) and phase duration ranging from 75-400 microseconds (us). Findings revealed that low-frequency stimulation at 1 Hz, combined with a phase duration between 150 us and 400 us, was the most energy-efficient while maintaining comfort, making it suitable for long-term use in wearable devices.

Study V explored the hemodynamic effects of frequency (1 Hz vs. 36 Hz) and plateau time using TTE-socks. Low-frequency 1 Hz NMES produced distinct single twitches that enhanced venous flow with minimal discomfort. In contrast, high-frequency 36 Hz NMES induced sustained tetanic contractions associated with greater discomfort but also higher hemodynamic efficacy. These findings underscore the importance of tailoring NMES parameters to individual needs for optimal compliance and therapeutic outcomes.

The thesis highlights the transformative potential of wearable NMES systems integrated into everyday garments to address physical inactivity-related health issues. By combining textile-based electrodes with optimized stimulation protocols, this research presents a user-friendly solution that may enhance comfort, mobility, and compliance. The integration of NMES into clothing has the potential to revolutionize preventive healthcare for populations at risk of VTE or unable to engage in regular physical activity due to aging or chronic conditions. Future research should focus on large-scale clinical trials to validate these findings and explore broader applications of wearable NMES technology across diverse medical contexts.

List of scientific papers

I. Euler L, Juthberg R, Flodin J, Guo L, Ackermann PW, Persson NK. Textile electrodes: influence of electrode construction and pressure on stimulation performance in neuromuscular electrical stimulation (NMES). Annu Int Conf IEEE Eng Med Biol Soc. 2021;2021:1305-1308. https://doi.org/10.1109/EMBC46164.2021.9630649

II. Schriwer E, Juthberg R, Flodin J, Ackermann PW. Motor point heatmap of the calf. J Neuroeng Rehabil. 2023 Mar;20(1):28. https://doi.org/10.1186/s12984-023-01152-5

III. Sundstrom C, Juthberg R, Flodin J, Guo L, Persson NK, Ackermann PW. Effects on hemodynamic enhancement and discomfort of a new textile electrode integrated in a sock during calf neuromuscular electrical stimulation. Eur J Appl Physiol. 2023 May;123(9):2013- 2022. https://doi.org/10.1007/s00421-023-05212-5

IV. Juthberg R, Flodin J, Guo L, Rodriguez S, Persson NK, Ackermann PW. Neuromuscular electrical stimulation in garments optimized for compliance. Eur J Appl Physiol. 2023 Apr;123(8):1739-1748. https://doi.org/10.1007/s00421-023-05181-9 (+ Correction Eur J Appl Physiol. 2023 Aug;123(8):1749 https://doi.org/10.1007/s00421-023-05211-6).

V. Juthberg R, Flodin J, Aliaga N, Guo L, Rodriguez S, Persson NK, Ackermann PW. Electrically Induced Hemodynamic Enhancement via Sock-Integrated Electrodes is More Comfortable and Efficient at 1 Hz as compared to 36 Hz. [Accepted]