The Effect of Vagus Nerve Stimulation on Lower Limb Muscle Strength and Balance in Nonelite Athletes

The vagus nerve (VN), the tenth cranial nerve, is a key component of the neuroendocrine-immune axis and plays a critical role in regulating autonomic functions such as cardiovascular, endocrine, respiratory, and digestive system activity through its extensive central and peripheral connections (1,2). Non-invasive vagus nerve stimulation (VNS), particularly through auricular stimulation, has been shown to modulate autonomic balance by reducing sympathetic activity, enhancing cardiac baroreflex sensitivity, and improving parasympathetic tone (3,4).

In the context of athletic performance, the autonomic nervous system's role in adaptation to training and recovery is well recognized (5). Post-exercise parasympathetic reactivation is increasingly used as a biomarker for recovery and performance enhancement. Auricular VNS (aVNS), by stimulating afferent auricular branches of the VN, may facilitate recovery by reducing exercise-induced fatigue, pain, and lactate accumulation, while improving parasympathetic activity (3). Importantly, these physiological effects have been observed without significant alterations in heart rate or blood pressure.

Balance training is a known contributor to improved functional performance in athletes, and neuromuscular control is essential for injury prevention and overall athletic capacity (6). Considering the limited research on the effects of aVNS on neuromuscular parameters such as muscle strength and balance response in non-elite athletic populations, this study aims to provide evidence on the efficacy of aVNS in this context.

This study is designed as a non-randomized controlled trial. Thirty non-elite athletes aged 18-35 years, who have been physically active for at least three months and currently exercise 2-5 days per week (averaging 3.2 hours per week), will be recruited. Eligible participants must have a BMI between 18.5 and 25 kg/m² and provide informed consent. Individuals with conditions affecting the inner or outer ear or BMI values outside the specified range will be excluded.

The intervention group will receive a single session of bilateral aVNS using a biphasic, asymmetric waveform at a frequency of 25 Hz, pulse width of 300 microseconds, applied continuously for 20 minutes. The post-intervention follow-up period will last 30 minutes (3).