Wearable Garment vs Gel Electrodes for Electrical Muscle Stimulation

Neurostimulation involves the use of electric current delivered through skin-surface electrodes to activate muscles. It is commonly used for purposes such as muscle strengthening, motor function improvement, blood flow enhancement, and in neuroprostheses. Standard neurostimulation systems typically rely on disposable hydrogel electrodes, which can cause skin irritation and tend to dry out over time. These limitations make hydrogel electrodes less suitable for long-term or repeated use.

Textile-based electrodes are an emerging alternative. These electrodes are integrated into wearable garments, making them washable, reusable, and more comfortable for extended wear times. However, research directly comparing their effectiveness and user experience compared to hydrogel electrodes is limited.

The goal of this study is to compare textile electrodes to gold-standard hydrogel electrodes for muscle activation and perceived stimulation sensation. The investigators hypothesize that: 1) there will be no clinically meaningful difference in participants' perception of the stimulation between textile and hydrogel electrodes, and 2) there will be no significant difference in the stimulation current required to elicit functional contractions.

This is a crossover randomized controlled trial involving three primary arms: 1) hydrogel electrodes, 2) dry polymer-textile electrodes with lotion, and 3) dry textile electrodes with gel pads applied. Each participant will perform all three arms in a randomized order with at least 24 hours between visits. Stimulation will be delivered to the calf and tibialis anterior muscles using the same electrical stimulator and settings in all conditions. Following completion of the three primary arms, participants will be given the option to complete an additional two arms using different types of commercially available moisturizers on the dry textile electrodes to assess comparative on-body performance of different water-based moisturizers. All moisturizers are commercially available and are labelled Skin Lotion A, B, and C in the 'Arms and Interventions' section.

A sample size of 18 participants is required to detect a Cohen's f of 0.40 with 95% power and a significance level of ⍺ = 0.05 for a within-subjects one-way repeated measures analysis of variance (ANOVA) with three conditions. To preserve statistical power, the investigators will recruit 20 participants. Pilot data comparing textile to hydrogel electrodes provided an estimated effect size of f = 0.65. Given the pilot data was not randomized, which likely inflated the observed effect size, the investigators conservatively based their sample size calculation on a Cohen's f of 0.40 (i.e., a large effect size) to ensure adequate power to detect a potentially smaller true effect.

A non-inferiority analysis will compare perceived stimulation intensity on a 10-point numerical rating scale. A 2-point difference is set as the non-inferiority margin based on prior research on the minimal clinically important difference. Textile electrodes will be considered non-inferior if the upper bound of the 95% confidence interval for the difference in intensity remains below this threshold. Repeated measures ANOVAs and Tukey's post hoc tests will be used to analyze the outcome variables where appropriate.

• Sensorimotor responses to electrical stimulation [Time frame: At each of the 5 study visits (Visit 1 through Visit 5) over approximately a 3-week period.]
• Kinematic recruitment curves [Time frame: At each of the 5 study visits (Visit 1 through Visit 5) over approximately a 3-week period.]
• Torque [Time frame: At each of the 5 study visits (Visit 1 through Visit 5) over approximately a 3-week period.]
• Sensation questionnaire [Time frame: At each of the 5 study visits (Visit 1 through Visit 5) over approximately a 3-week period.]
• Skin-electrode impedance [Time frame: At each of the 5 study visits (Visit 1 through Visit 5) over approximately a 3-week period.]