Neuromodulation of the Autonomic Nervous System in Athletes

Several studies have shown that transcutaneous vagus nerve stimulation (tVNS) potentially exhibits therapeutic effects similar to its invasive counterpart. tVNS is performed using surface electrodes and low-frequency electrical currents, targeting specific locations, most commonly the auricular branch of the vagus nerve or its cervical branch.

Stimulation of the auricular branch of the vagus nerve activates vagal sensory fibers, simulating sensory input to the brainstem and forming what is known as the auriculo-vagal afferent pathway. Since these fibers project directly to the nucleus of the solitary tract (also known as the solitary tract nucleus), which in turn has direct or indirect projections to nuclei that provide noradrenergic, endorphinergic, and serotonergic fibers in various parts of the brain, regulating systemic parameters of cardiovascular, respiratory, and immune functions, it can be expected that the body's response to stimulation of the auricular branch of the vagus nerve will be systemic.

With the onset of physical exercise, sympathetic activity in the body increases and reaches a plateau value after a certain period of maximum activity. After the end of physical exercise, suppressed parasympathetic activity begins to intensify, and the sympathetic system gradually returns to a resting state. After training, parasympathetic system activation continues for up to 48 hours. In certain types of training, when the frequency of anaerobic respiration increases during physical exertion, a decrease in parasympathetic reactivation may be observed.

In the literature, there are individual studies that have evaluated the effects of transcutaneous stimulation of the auricular branch of the vagus nerve for sports purposes (to accelerate recovery processes after physical exertion). It has been demonstrated that tVNS in athletes improves heart rate recovery, reduces lactate levels in plasma, reduces pain sensations, decreases overtraining syndrome, and reduces fatigue levels.

The aim of this study is to: evaluate the influence of low-frequency electrical stimulation of the auricular branch of the vagus nerve on the functional reserve of the cardiovascular and respiratory systems in athletes during the post-training period, after high-intensity workouts.

Inclusion criteria

• Professional athletes over the age of 15 and under the age of 35;
• Cyclic sports (swimming, modern pentathlon, athletics, triathlon);
• Difficult coordination sports (dance sports, rhythmic gymnastics);
• Sports category: no lower than candidate for master of sports;
• Voluntary informed consent.

Exclusion criteria

• Atypical and unrelated to physical exertion changes on the ECG (T wave inversion, st-segment depression, pathological Q waves, signs of left atrial enlargement, signs of right ventricular hypertrophy, ventricular pre-excitation, complete right or left bundle branch block, prolonged or shortened Q-T interval, Brugada-like early repolarization);
• Heart rhythm and conduction disorders (frequent ventricular and supraventricular extrasystoles, first-degree atrioventricular block (P-Q > 0.21 s, not shortened during hyperventilation or physical exertion), second or third degree);
• Expressed sinus bradycardia with resting heart rate < 40 bpm;
• Taking glucocorticosteroids in the last 1 month;
• Taking any antiarrhythmic drugs, including beta-blockers.