Effect of Single-Session HVPGS on Hand Grip Strength and Reaction Time in Healthy Individuals

Background and Rationale:Neuromuscular Electrical Stimulation (NMES) is widely utilized to enhance force production and neural excitability in both clinical and sports settings. High-Voltage Pulsed Galvanic Stimulation (HVPGS) is a unique electrotherapeutic modality characterized by an ultra-short pulse duration and high-voltage peak intensity. Due to its specific wave architecture, HVPGS exhibits reduced capacitive skin impedance, allowing electrical current to penetrate deeper into muscle bellies with minimal cutaneous discomfort. While conventional NMES protocols often induce acute localized fatigue, HVPGS has shown potential as an acute peripheral priming tool. However, evidence regarding its immediate, single-session effects on concurrent motor output (grip strength) and central sensorimotor processing speed (reaction time) remains limited.Study Design and Setting:This cross-sectional, single-arm interventional study was conducted in the Orthopedic Rehabilitation Unit of the School of Physical Therapy and Rehabilitation at Kırşehir Ahi Evran University. The protocol was approved by the Clinical Research Ethics Committee of Kırşehir Ahi Evran University (Approval Number: 2025-15/191) and executed in compliance with the Declaration of Helsinki.Participants and Eligibility:A sample of 42 healthy volunteers aged 18 to 65 years was enrolled, including university academic/administrative staff and senior physical therapy students. Sample size was determined via a priori power analysis in G*Power 3.1.9.2 ($d = 0.79$, $\alpha = 0.05$, $1-\beta = 0.80$). Exclusion criteria comprised any self-reported neck or upper extremity discomfort/pain within the preceding 6 months or neurological disorders affecting sensation and motor execution.Study Procedures and Intervention:Baseline Assessment (T0): Participants completed baseline evaluations of bilateral isometric hand grip strength using a Jamar hydraulic hand dynamometer (seated position, 90° elbow flexion; 3 consecutive trials averaged in kg) and sensorimotor reaction time using the Nelson Hand Reaction Test (5 trials, middle 3 trials averaged in cm).Electrostimulation Intervention: Participants received a single session of HVPGS applied to the forearm flexor muscle group (m. flexor digitorum superficialis, m. flexor digitorum profundus, and m. flexor pollicis longus). The intervention followed an intermittent duty cycle consisting of 7 seconds of active stimulation followed by 14 seconds of rest. The procedure was directly supervised by an expert physiotherapist with 21 years of clinical experience in electrotherapy.Post-Intervention Assessment (T1): Immediately following the completion of the HVPGS session, identical grip strength and reaction time measurements were conducted to record acute functional changes.Statistical Analysis:Data analysis was performed using R statistical software. Pre- and post-intervention changes ($\Delta = \text{Post} - \text{Pre}$) were calculated. Normality was evaluated via Shapiro-Wilk tests. Depending on distributional normality, paired-samples t-tests or Wilcoxon signed-rank tests were executed to detect immediate therapeutic changes. Secondary interactions with demographic variables (Age, BMI) and subgroups (Sex, Hand Dominance) were analyzed using Pearson/Spearman correlation coefficients and independent t-tests / Mann-Whitney U tests.