This study evaluated the hemodynamic effects, discomfort, and energy efficiency of low-intensity neuromuscular electrical stimulation (LI-NMES) of the calf delivered via sock-integrated transverse textile electrodes (TTE) at different frequencies and plateau times. Fifteen healthy participants underwent NMES stimulation through 3 × 3 cm TTE with ten combinations of frequency (1–36 Hz) and plateau times (0.5–7 s). NMES was increased until plantar flexion occurred, at which point ultrasound-measurements were made of popliteal peak venous velocity (PVV), time-averaged mean velocity (TAMV), average duration of blood flow pulse (ADBP) and ejection volume (EV). Discomfort (NRS, 0–10), current amplitude, and energy consumption were recorded. Median values were analyzed with significance set at p < 0.05. Both 1 Hz and 36 Hz C-LI-NMES significantly improved PVV and TAMV (p ≤ 0.008). EV increased significantly for plateau times of 1.5, 5.0, and 7.0 s (p < 0.05). Compared to 36 Hz, 1 Hz showed significantly lower discomfort (NRS: 0.4 vs. 1.6) and energy consumption (0.4 vs. 31.3 mJ, both p ≤ 0.01) but required higher current amplitude (33.2 vs. 23.3 mA, p < 0.01) to reach plantar flexion. The study concludes that both 1 Hz and 36 Hz frequency improve venous hemodynamics, but 1 Hz stimulation minimizes discomfort and energy use while maintaining effectiveness. Trial registration: Retrospectively registered with Clinical Trials, trial ID: NCT06082297.

This paper presents a low-noise bioimpedance (bio-Z) spectroscopy interface for electrical impedance myography (EIM) over the 1 kHz to 2 MHz frequency range. The proposed interface employs a sinusoidal signal generator based on direct-digital-synthesis (DDS) to improve the accuracy of the bio-Z reading, and a quadrature low-intermediate frequency (IF) readout to achieve a good noise-to-power efficiency and the required data throughput to detect muscle contractions. The readout is able to measure baseline and time-varying bio-Z by employing robust and power-efficient low-gain IAs and sixth-order single-bit bandpass (BP) ΔΣ ADCs. The proposed bio-Z spectroscopy interface is implemented in a 180 nm CMOS process, consumes 344.3 - 479.3 μ W, and occupies 5.4 mm 2 area. Measurement results show 0.7 mΩ/√Hz sensitivity at 15.625 kHz, 105.8 dB SNR within 4 Hz bandwidth, and a 146.5 dB figure-of-merit. Additionally, recording of EIM in time and frequency domain during contractions of the bicep brachii muscle demonstrates the potential of the proposed bio-Z interface for wearable EIM systems.

This paper presents a 16-channel analog frontend (AFE) for wearable multi-channel surface electromyography recording. The proposed architecture adopts frequency-division multiplexing (FDM), enabling extensive sharing of signal conditioning circuitry and requiring only three cables for transmission to an external back-end for digital signal processing. Benefiting from the up-conversion process, the FDM signal exhibits robustness against cable motion artifacts and mains interference, allowing short-distance communication without compromising signal quality. This work achieves a channel-to-cable ratio of 16:3, dramatically reducing system complexity. Implemented in a 180 nm CMOS technology, the proposed 16-channel AFE occupies only 6.42 mm2 and consumes 40.1 µW per channel from a 1.5 V supply. Measurements on a forearm demonstrate the capability to simultaneously detect muscle activation from various muscle groups, showcasing its potential for gesture recognition applications.

Neuromuscular electrical stimulation (NMES) is a self-directed home based therapeutic tool in early rehabilitation for musculoskeletal (MSK) conditions. However, the effectiveness of traditional NMES is fundamentally constrained by muscle fatigue. To address this limitation, this work proposes a detection system, which simultaneously records multifrequency electrical impedance myography (EIM) and surface electromyography(sEMG) in real time for time-frequency analysis of muscle activation, contraction, and fatigue. To demonstrate the ability to monitor these muscle physiological states, two experiments involving weightless and weighted dynamic contractions of the biceps brachii muscle were performed. Results from these experiments show synchronous changes in sEMG and EIM spectra during contractions, and clear trends in sEMG’s mean power frequency (MPF) and EIM spectra with fatigue progression. Additionally, the configurable 4-channel NMES has been electrically evaluated for clinical use, demonstrating the feasibility of the proposed system for closed-loop stimulation. This work showcases the potential of sEMG and multi-frequency EIM to enhance the effectiveness of NMES for MSK conditions by capturing the behavior of distinct mechanisms of muscle fatigue.

Biopotential acquisition chopper instrumentation amplifiers require a dc-servo loop (DSL) in order to filter electrode dc offsets. However, the noise performance degradation due to the addition of the DSL is often overlooked despite that it can be very detrimental at the frequencies of interest. This article presents an in-depth noise analysis of biopotential acquisition chopper instrumentation amplifiers with analog DSLs. Analytical expressions that predict the noise of different DSL implementations are found and a design flow to minimize their noise contribution is proposed. The design methodology is demonstrated with example circuits targeting biopotential recording systems. These circuits are implemented using a standard 180 nm CMOS technology, and their performance is verified through postlayout simulations. The findings of this work provide a comprehensive understanding of the noise characteristics of a DSL, its impact on noise performance, and design strategies for noise optimization.

The ability to perform accurate continuous glucose monitoring without blood sampling has revolutionised the management of diabetes. Newer methods that can allow measurements during longer periods are necessary to substantially improve patients’ quality of life. This paper presents an alternative method for glucose monitoring which is based on electrical impedance spectroscopy. A battery-less implantable bioimpedance spectroscope was designed, built, and used in an in vivo study on pigs. After a recovery period of 14 days post surgery, a total of 236 subcutaneous bioimpedance measurements obtained from intravenous glucose tolerance tests, with glucose concentration ranges between 77.4 and 523.8 mg/dL, were analyzed. The results show that glucose concentrations estimated by subcutaneous bioimpedance measurements correlate very well to the blood glucose reference values. The pigs were clinically healthy throughout the study, and the postmortem examinations revealed no signs of adverse effects related to the sensor. The implantation of the sensor requires minor surgery. The implant, being externally powered, could in principle last indefinitely. These encouraging results demonstrate the potential of the bioimpedance method to be used in future continuous glucose monitoring systems.

This brief presents an integrated solution to over-current protection in neuromuscular stimulators. The proposed approach provides fast detection of a single-fault condition, i.e., unintentional electrode short circuit or malfunction of the stimulator, thereby preventing prolonged high-intensity currents from flowing into tissues. In addition, a programmable current threshold enables the system to be also used for monitoring the stimulation intensity. The proposed solution was designed in a 180 nm high-voltage CMOS technology, and its functionality was verified by post-layout simulations in which the safety mechanisms were tested under fault conditions. The implementation only occupies an area of 0.286 mm2, making it feasible to be embedded in fully integrated NMES stimulators while providing the required patient safety.

Neuromuscular electrical stimulation (NMES) requires voltages exceeding several tens of volts which are typically obtained by using DC-DC boost converters. However, these converters incorporate a large external inductor, which hinders integration and severely restricts the minimum size of the stimulator. This paper presents a charge pump (CP) high-voltage generator particularly designed for NMES applications. The proposed hybrid CP comprises a low-voltage latched CP followed by a high-voltage Dickson CP with boosted pumping clocks. This architecture generates an output voltage of 40.5 V from a 3.3 V supply, enabling the delivery of up to 30 mA stimulation pulses at a maximum frequency of 50 Hz. The circuit is designed in a 180 nm HV CMOS process and occupies a silicon area of 2.7 mm 2 . By eliminating the inductor and requiring only one external storage capacitor, this design has the potential of being used in compact stimulators for wearable medical applications.

Purpose: Physical inactivity is associated with muscle atrophy and venous thromboembolism, which may be prevented by neuromuscular electrical stimulation (NMES). This study aimed to investigate the effect on discomfort, current amplitude and energy consumption when varying the frequency and phase duration of low-intensity NMES (LI-NMES) via a sock with knitting-integrated transverse textile electrodes (TTE). Methods: On eleven healthy participants (four females), calf-NMES via a TTE sock was applied with increasing intensity (mA) until ankle-plantar flexion at which point outcomes were compared when testing frequencies 1, 3, 10 and 36 Hz and phase durations 75, 150, 200, 300 and 400 µs. Discomfort was assessed with a numerical rating scale (NRS, 0–10) and energy consumption was calculated and expressed in milli-Joule (mJ). Significance set to p ≤ 0.05. Results: 1 Hz yielded a median (inter-quartile range) NRS of 2.4 (1.0–3.4), significantly lower than both 3 Hz with NRS 2.8 (1.8–4.2), and 10 Hz with NRS 3.4 (1.4–5.4) (both p ≤.014). Each increase in tested frequency resulted in significantly higher energy consumption, e.g. 0.6 mJ (0.5–0.8) for 1 Hz vs 14.9 mJ (12.3–21.2) for 36 Hz (p =.003). Longer phase durations had no significant effect on discomfort despite generally requiring significantly lower current amplitudes. Phase durations 150, 200 and 400 µs required significantly lower energy consumption compared to 75 µs (all p ≤.037). Conclusion: LI-NMES applied via a TTE sock produces a relevant plantar flexion of the ankle with the best comfort and lowest energy consumption using 1 Hz and phase durations 150, 200 or 400 µs.

Objective: Electrical impedance myography (EIM) measures bioimpedance over muscles. This paper proposes a circuit-based modelling methodology originated from finite element analysis (FEA), to emulate tissues and effects from anthropometric variations, and electrode placements, on EIM measurements. The proposed methodology is demonstrated on the upper arms and lower legs. Methods: FEA evaluates impedance spectra (Z-parameters), sensitivity, and volume impedance density for variations of subcutaneous fat thickness (tf), muscle thickness (tm), and inter-electrode distance (IED), on limb models over 1Hz-1MHz frequency range. The limbs models are based on simplified anatomical data and dielectric properties from published sources. Contributions of tissues to the total impedance are computed from impedance sensitivity and density. FEA Z-parameters are imported into a circuit design environment, and used to develop a three Cole dispersion circuit-based model. FEA and circuit model simulation results are compared with measurements on ten human subjects. Results: Muscle contributions are maximized at 31.25kHz and 62.5kHz for the upper arm and lower leg, respectively, at 4cm IED. The circuit model emulates variations in tf and tm, and simulates up to 89 times faster than FEA. The circuit model matches subjects measurements with RMS errors < 36.43 and < 17.28, while FEA does with < 36.59 and < 4.36. Conclusions: We demonstrate that FEA is able to estimate the optimal frequencies and electrode placements, and circuit-based modelling can accurately emulate the limbs bioimpedance. Significance: The proposed methodology facilitates studying the impact of biophysical principles on EIM, enabling the development of future EIM acquisition systems.