Unilateral and Bilateral taVNS in Fibromyalgia

Fibromyalgia syndrome (FMS) is a chronic condition characterized by widespread pain, fatigue, sleep disturbances, and psychological symptoms, often associated with autonomic nervous system dysfunction. Reduced heart rate variability (HRV) and increased sympathetic activity are commonly observed in individuals with FMS, contributing to impaired exercise tolerance and reduced quality of life.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that targets the auricular branch of the vagus nerve and has been shown to influence autonomic regulation and central pain processing. However, evidence regarding its effects on exercise performance and the comparative efficacy of unilateral versus bilateral stimulation remains limited.

This study was designed as a randomized controlled trial including individuals diagnosed with fibromyalgia. Participants were allocated into three groups: unilateral taVNS, bilateral taVNS, and a home exercise program. The interventions were applied over a two-week period consisting of ten sessions. The taVNS intervention was administered via auricular stimulation targeting vagal afferents, while the exercise group followed a structured home-based program.

Outcome measures included clinical symptom scales (FIQ, BAI, BDI, PSQI), autonomic nervous system parameters derived from HRV analysis (including RMSSD, pNN50, LF, HF, and LF/HF ratio), and exercise performance assessed through repetition capacity. Assessments were conducted before and after the intervention period.

The primary objective was to compare the effects of unilateral and bilateral taVNS on autonomic function and exercise performance, and to evaluate whether combining neuromodulation with exercise provides additional clinical benefits in individuals with fibromyalgia. The results of this study may help inform rehabilitation strategies integrating neuromodulation and exercise-based interventions.

Inclusion criteria

• Were between 18 and 45 years of age
• Were diagnosed with fibromyalgia according to the 2016 ACR diagnostic criteria

-- Stable clinical condition

• Ability to understand and follow study procedures
• Willingness to participate and provide informed consent

Exclusion criteria

• A history of malignancy
• Cardiopulmonary diseases contraindicating exercise
• Limb loss
• Ear infections and implants, implanted electronic devices
• Systemic diseases (hematological, endocrine, rheumatological, renal, cardiovascular, gastrointestinal, neurological, or autoimmune diseases)
• Active infection
• Surgery or major trauma within the previous 6 months
• Postmenopausal status
• Pregnancy or lactation