Comparison of the Acute Effects of Auricular Vagus Nerve Stimulation and Deep Breathing Exercise on the Autonomic Nervous System Activity and Biomechanical Properties of the Muscle in Healthy People

<b>Background/Objectives:</b> We aimed to examine the acute effects of deep breathing exercise and transcutaneous auricular vagus nerve stimulation (taVNS) on autonomic nervous system activation and the characteristics of certain muscle groups and to compare these two methods. <b>Methods:</b> 60 healthy adults between the ages of 18 and 45 were randomly divided into two groups to receive a single session of taVNS and deep breathing exercises. Acute measurements of pulse, blood pressure, perceived stress scale, autonomic activity, and muscle properties were performed before and after the application. <b>Results:</b> A significant decrease was detected in the findings regarding the perceived stress scale, pulse, and blood pressure values as a result of a single session application in both groups (<i>p</i> < 0.05). In addition, it was determined that the findings regarding autonomic measurement values increased in favor of the parasympathetic nervous system in both groups (<i>p</i> < 0.05). In measurements of the structural properties of the muscle, the stiffness values of the muscles examined in both groups decreased (<i>p</i> < 0.05), while the findings regarding relaxation increased (<i>p</i> < 0.05), except for the masseter in the deep breathing (DB) group. As a result of the comparative statistical evaluation between the groups, the increase in parasympathetic activity was found to be greater in the DB group according to root mean square of differences in successive RR intervals (RMSSD), the percent of differences in adjacent RR intervals > 50 ms (pNN50), and stress index parameters (<i>p</i> < 0.05). In the measurements made with the Myoton^®PRO device, the increase in the relaxation value was higher in the gastrocnemius muscle of the VNS group (<i>p</i> < 0.05). <b>Conclusions:</b> It has been observed that both methods can increase parasympathetic activity and muscle relaxation in healthy people in a single session. However, DB appears to be slightly superior in increasing parasympathetic activity, and VNS appears to be slightly superior in increasing relaxation.