Interventions to mitigate pain and reduce skin impedance during neuromuscular electrical stimulation

Objective: High skin-electrode impedance limits neuromuscular electrical stimulation (NMES) by increasing discomfort and impairing efficacy. This study compared the effects of mechanical exfoliation and gel pad (hydrogel) application on skin impedance, NMES current intensity, and pain perception. Methods: In a within-subject design, 49 healthy participants (28 males, 21 females) received NMES on both calves with randomized interventions (dry electrode, gel pad, exfoliation, combined). Impedance, NMES current intensity and pain (Numerical Pain Rating Scale, NPRS, 0-10 (no-maximum pain)) at plantar flexion (PF) were recorded. Results: Gel pads produced the largest impedance reduction (∼10 kΩ) in participants reaching PF at lower intensities (PF range: 5-20 mA). All interventions significantly reduced impedance (∼1.5 kΩ) and current intensity (∼1 mA) at PF versus dry electrodes (p < 0.001). Gel pads, alone or combined with exfoliation, reduced pain by ∼ 1 NPRS point (p < 0.001), while exfoliation alone had no effect. Over 20% of participants reported persistent pain (NPRS ≥ 4) despite interventions. Higher impedance was significantly associated with lower physical activity level. Conclusion: Gel pads effectively reduced both impedance and pain during NMES, while exfoliation reduced impedance without affecting pain. Significance: Hydrogel pads improve NMES tolerability, yet persistent discomfort warrants improved skin-electrode interfaces.