Muscles play an indispensable role in human life. Surface electromyography (sEMG), as a non-invasive method, is crucial for monitoring muscle status. It is characterized by its real-time, portable nature and is extensively utilized in sports and rehabilitation sciences. This study proposed a wireless acquisition system based on multi-channel sEMG for objective monitoring of grip force. The system consists of an sEMG acquisition module containing four-channel discrete terminals and a host computer receiver module, using Bluetooth wireless transmission. The system is portable, wearable, low-cost, and easy to operate. Leveraging the system, an experiment for grip force prediction was designed, employing the bald eagle search (BES) algorithm to enhance the Random Forest (RF) algorithm. This approach established a grip force prediction model based on dual-channel sEMG signals. As tested, the performance of acquisition terminal proceeded as follows: the gain was up to 1125 times, and the common mode rejection ratio (CMRR) remained high in the sEMG signal band range (96.94 dB (100 Hz), 84.12 dB (500 Hz)), while the performance of the grip force prediction algorithm had an R² of 0.9215, an MAE of 1.0637, and an MSE of 1.7479. The proposed system demonstrates excellent performance in real-time signal acquisition and grip force prediction, proving to be an effective muscle status monitoring tool for rehabilitation, training, disease condition surveillance and scientific fitness applications.

Transcutaneous electrical nerve stimulation (TENS) is constrained by high skin impedance and unstable electrode contact. This study proposes a novel composite electrode system comprising a polyvinyl alcohol/silver (PVA/Ag) microneedle array and a highly conductive polyacrylamide/lithium chloride (PAAm/LiCl) hydrogel. The PVA/Ag microneedles (~365 µm in height, ~48 µm tip diameter) possess sufficient mechanical strength to penetrate the stratum corneum, establishing a low-resistance pathway. The complementary PAAm/LiCl hydrogel exhibits high conductivity (10.28 S/m) and mechanical flexibility, further optimizing the interface contact. The experimental results demonstrate that this composite system achieves low electrochemical impedance and induces stable, clear electromyographic responses in vivo. It effectively addresses the common issues of electrode detachment and signal attenuation associated with conventional electrodes, offering a promising hardware solution for efficient and comfortable wearable rehabilitation devices.

Transcutaneous electrical stimulation (TES) is a non-invasive technique that delivers electrical currents through the skin to modulate peripheral neural and muscular activity. However, conventional surface stimulation often exhibits limited spatial selectivity because current spreads across superficial and deep tissues. To investigate physical principles that may inform future transcutaneous applications without assuming anatomical or physiological fidelity, this study developed a finite-element framework based on an idealized multilayer cylindrical limb model. The model represented skin, adipose tissue, muscle, cortical bone, and bone marrow using concentric tissue domains parameterized with averaged forearm dimensions and literature-derived electrical properties. Two-dimensional and three-dimensional surface-electrode montages were evaluated by varying return-electrode positions, axial electrode spacing, and inter-channel current ratios. The simulations showed that electrode configuration influenced the location, volume, and compactness of high-maximum-envelope-modulation-amplitude (MEMA) regions. Within the investigated idealized geometry, intermediate return-electrode angles (approximately θ₂ = 130–150°) produced more centrally distributed intramuscular high-MEMA regions, whereas current-ratio modulation shifted the MEMA_max-defined field maximum under fixed electrodes. These results demonstrate the computational feasibility of regulating TI electric-field distributions in a controlled virtual model rather than physiological selectivity or clinical efficacy. Translation to actual transcutaneous stimulation will require staged validation using anatomically realistic models, physical phantoms, physiological experiments, and ultimately human studies.