The Effects of Vagus Nerve Stimulation on Stress, Competitive Anxiety, and Depression in Elite Shooters: Randomized Controlled Trial

Abstract

This study aimed to determine whether vagus nerve stimulation is effective in modulating psychological states such as anxiety, depression, and stress in elite shooters. A total of 18 female elite shooters (aged 18–19 years) were randomly assigned to either an experimental group (n = 9) or a control group (n = 9). The experimental group received vagus nerve stimulation for 30 min per session, once daily, seven days a week, over a period of four weeks. Psychological variables were assessed at three time points: pre-test (baseline), mid-test (2 weeks), and post-test (4 weeks). Two-way repeated measures ANOVA revealed significant group × time interactions for stress (p < 0.01), cognitive anxiety (p < 0.001), somatic anxiety (p < 0.01), confidence (p < 0.001), and depression (p < 0.01). Paired t-tests demonstrated significant reductions in stress, cognitive anxiety, somatic anxiety, and depression, as well as a significant increase in confidence within the experimental group. These findings provide compelling evidence that a 4-week course of vagus nerve stimulation can reduce stress, anxiety, and depression while enhancing confidence in elite shooters. Therefore, this intervention may serve as a beneficial strategy for improving mental health in elite shooters.

1. Introduction

Recent neuropsychological research has increasingly focused on elucidating the influence of the nervous system on psychological variables in humans, including arousal, attention, perception, memory, language, thought, emotion, and motivation. This body of work also seeks to identify causal relationships between neural stimuli and psychological outcomes. In particular, there is growing recognition that the nervous system may play a therapeutic role in mitigating negative psychological conditions such as stress, anxiety, and depression-related sleep disturbances.

Aligned with the framework of general adaptation syndrome, stress has been conceptualized as a sequence of universal physiological responses triggered by environmental demands, ultimately leading to a state of physical disequilibrium [1]. Among athletes, repeated exposure to competition-related stress has been shown to diminish vagal sensitivity to the heart and induce relative sympathetic hyperactivity, thereby contributing to the development of cardiovascular and metabolic disorders [2]. Accordingly, robust vagal regulation is interpreted as a strong physiological capacity to cope with stress, whereas reduced vagal tone reflects heightened vulnerability [3]. Moreover, vagus nerve stimulation has demonstrated antidepressant effects and may influence the perception and regulation of anxiety by transmitting afferent signals to key brain regions involved in anxiety processing, including the locus coeruleus, orbitofrontal cortex, insula, hippocampus, and amygdala [4].

In relation to neuropsychological functioning, previous studies have reported that various forms of neuropsychological stimulation can enhance attentional capacity in children with attention deficit disorder, as assessed using standardized test batteries [5]. Similarly, research on vagus nerve stimulation using transcutaneous electrical nerve stimulation (TENS) has shown increased parasympathetic activity, as reflected in changes in blood pressure and heart rate variability [6]. These findings support the hypothesis that when autonomic imbalance contributes to disorders such as dysautonomia, stimulation of the vagus nerve via TENS may help restore autonomic homeostasis and stabilize both psychological and physiological states. From this perspective, vagus nerve stimulation may hold particular utility in the realm of competitive sports. For example, studies have shown that transcutaneous vagus nerve stimulation (tVNS) improved anxiety levels during motor tasks such as golf tee shots and baseball pitching, suggesting that such stimulation may enhance athletic performance under pressure [7]. Additionally, improvements in fatigue, pain, and autonomic function observed during cycling in youth athletes further support the performance-enhancing potential of vagus nerve stimulation [8].

Building on these prior findings, a growing number of strategies have been proposed to enhance athletic performance. Athletic development is increasingly viewed as a nonlinear, self-organizing process [9], whereby the integration of diverse training methods contributes to the advancement of athlete capabilities [10,11]. Several studies have applied neuropsychological approaches within sports contexts, including investigations into the relationship between cardiac autonomic nervous system activity and athletic performance [12], the effects of dance sport exercise on neurotransmitter levels and attentional capacity in adolescents [13], and the association between neurocognitive scores and dual-task gait in retired athletes [14]. The influence of vagus nerve stimulation on changes in athletic performance has also been explored [15], underscoring its relevance in sports science. In particular, the role of vagus nerve stimulation may be especially pertinent in sports that demand high levels of concentration and psychological stability, such as shooting. In these disciplines, verifying the efficacy of vagus nerve stimulation in regulating stress, mitigating anxiety, and alleviating depressive symptoms is essential for maintaining mental stability and minimizing performance variability. Collectively, the above findings provide a rationale for evaluating the potential benefits of vagus nerve stimulation in the context of competitive shooting. Accordingly, the present study was designed to determine whether vagus nerve stimulation could positively influence emotional states—specifically anxiety, depression, and stress—among elite shooters.

2. Methods

2.1. Participants

Thirty-five participants were enrolled as registered athletes of the Korean Shooting Federation. The following criteria excluded participants from participating in the study protocol: (1) Registered as a shooter with the Korea Shooting Federation for at least 5 years; (2) not receiving hormone replacement treatment; (3) diagnosed with major depression, bipolar disorder, or schizophrenia (Diagnostic and Statistical Manual of Mental Disorders: DSM-IV) within the past year; and (4) diagnosed with mental symptoms such as anxiety and agitation within the past three months.

The final participants of 18 female elite shooters (aged range: 18–19 years) were randomly assigned into the experimental group (n = 9, 18.67 ± 0.50 years) and the control group (n = 9, 18.44 ± 0.53 years). The participant sample size was calculated using ANOVA with a moderate effect size of 0.30, a significance level of 0.05, and a power of 0.95 (G*power 3.2.1).

All participants were successfully shielded from recognizing their own directional preference by not discussing this study concept with them. Randomization assignment was computer generated and conducted by the statistician. The study goals and methodology were explained to all subjects who agreed to participate to ensure complete understanding, and the study complied with the ethical standards of the Declaration of Helsinki. All subjects and their parents signed an informed consent form before participation. Approval for procedures was obtained from the human subjects committee of the Institutional Review Board at Incheon National University (7007971-202209-002A).

2.2. Procedure

To assess the effects of vagus nerve stimulation on psychological outcomes, the experimental group received stimulation once daily, seven days per week, for a total duration of four weeks. Stress, anxiety, and depression levels were measured at three time points: prior to the intervention (pre-test), at two weeks (mid-test), and at four weeks (post-test). The control group did not receive any vagus nerve stimulation but completed the same psychological assessments at the same time intervals as the experimental group.

2.3. Psychologic Measure

To assess stress levels in participants, the Korean version of the Perceived Stress Scale (PSS) was employed. Originally developed by Cohen et al. as a 10-item instrument, the scale has demonstrated strong reliability and validity across various populations [16]. For the present study, the Korean adaptation of the 10-item PSS validated by Lee et al. was utilized [17].

Anxiety levels were evaluated using the Competitive State Anxiety Inventory-2 (CSAI-2), developed by Martens et al. [18]. This self-report questionnaire consists of 27 items and comprises three subscales: cognitive state anxiety, somatic state anxiety, and state self-confidence. Each subscale includes 9 items, rated on a Likert scale, with scores ranging from 9 to 36. Higher scores indicate greater intensity of the respective psychological state—either anxiety or self-confidence—immediately prior to competition.

Depression was assessed using the Beck Depression Inventory-II (BDI-II), a widely used 21-item self-administered scale designed to measure the severity of depressive symptoms in adults and adolescents [19]. Respondents selected the statement that best described how they had felt over the previous two weeks, including the current day. Each item is rated on a 4-point scale (0 to 3), with total scores representing the sum of all item responses. A total score of 0–13 indicates minimal depression, 14–19 mild, 20–28 moderate, and 29–63 severe depression.

2.4. Vagus Nerve Stimulation (VNS)

Vagus nerve stimulation in the experimental group was administered using a noninvasive auricular stimulator designed for mental health enhancement (Healaon, Nurive Co., Ltd., Seoul, Republic of Korea). The stimulation was delivered via electrodes positioned on the bilateral cymba conchae of the auricle, regions richly innervated by the auricular branch of the vagus nerve. Prior to stimulation, the auricular skin was disinfected with alcohol, and the device was securely fitted to both ears, as illustrated in Figure 1. The stimulation protocol was based on previously validated parameters known to enhance vagal efferent activity: a train on-time of 2 s, off-time of 3 s, pulse width of 0.5 s, pulse frequency of 10 Hz, and pulse amplitude ranging from 2.0 to 2.7 mA.

Each session lasted 30 min and was administered once daily, seven days per week, over a period of four weeks.

2.5. Statistical Analysis

All data are presented as mean ± standard deviation. Statistical analyses were conducted using SPSS Statistics for Windows, version 25.0 (IBM Corp., Armonk, NY, USA). A two-way repeated measures ANOVA was performed to assess interaction effects (group × time) for all outcome variables across three time points (pre-test, mid-test, and post-test) between the experimental and control groups. When significant interactions were observed, post hoc paired t-tests were conducted to identify differences between time points. A p-value of less than 0.05 was considered statistically significant.

3. Results

3.1. Changes in Stress Levels in Response to Vagus Nerve Stimulation

The baseline statistics are pre-test (17.00 ± 5.29), mid-test (16.55 ± 7.38), and post-test (7.11 ± 6.23) in the experimental group and pre-test (17.66 ± 7.36), mid-test (17.22 ± 7.61), and post-test (22.00 ± 9.36) in the control group. Two-way repeated measures ANOVA significant group × time interaction for stress (p < 0.01) (Figure 2). The paired t-test showed that stress was significantly decreased in the experimental group between pre to post (p < 0.01) and mid to post (p < 0.001), but no significant changes were observed in the control group.

3.2. Changes in Competitive State Anxiety Levels in Response to Vagus Nerve Stimulation

Figure 3 shows the cognitive anxiety following vagus nerve stimulation. The baseline statistics are pre-test (24.22 ± 7.56), mid-test (18.55 ± 9.09), and post-test (9.33 ± 8.15) in the experimental group and pre-test (18.88 ± 4.34), mid-test (19.11 ± 4.80), and post-test (18.88 ± 7.85) in the control group. Two-way repeated measures ANOVA significant group × time interaction for cognitive anxiety scores (p < 0.001) (Figure 3). Paired t-test showed that cognitive anxiety was significantly decreased in the experimental group between pre to post (p < 0.001), pre to mid (p < 0.01), and mid to post (p < 0.01), but no significant changes were observed in the control group.

Figure 4 shows the somatic anxiety following vagus nerve stimulation. The baseline statistics are pre-test (20.11 ± 8.96), mid-test (12.66 ± 7.90), and post-test (7.88 ± 5.73) in the experimental group and pre-test (18.44 ± 7.21), mid-test (19.11 ± 6.67), and post-test (18.00 ± 5.93) in the control group. Two-way repeated measures ANOVA significant group × time interaction for somatic anxiety (p < 0.01) (Figure 4). The paired t-test showed that somatic anxiety was significantly decreased in the experimental group between pre to post (p < 0.01) and pre to mid (p < 0.001), but no significant changes were observed in the control group.

Figure 5 shows confidence following vagus nerve stimulation. The baseline statistics are pre-test (13.88 ± 4.37), mid-test (19.11 ± 6.50), and post-test (26.55 ± 6.16) in the experimental group and pre-test (17.22 ± 3.49), mid-test (17.66 ± 6.40), and post-test (14.55 ± 7.51) in the control group. Two-way repeated measures ANOVA significant group × time interaction for confidence (p < 0.001) (Figure 5). The paired t-test showed that confidence was significantly increased in the experimental group between pre to post (p < 0.001), pre to mid (p < 0.05), and mid to post (p < 0.01), but no significant changes were observed in the control group.

3.3. Changes in Depression in Elite Shooters Following Vagus Nerve Stimulation

The baseline statistics are pre-test (19.22 ± 5.23), mid-test (12.33 ± 9.73), and post-test (3.55 ± 5.59) in the experimental group and pre-test (17.00 ± 11.58), mid-test (10.22 ± 9.09), and post-test (13.00 ± 13.09) in the control group. Two-way repeated measures ANOVA significant group × time interaction for depression (p < 0.01) (Figure 6). Paired t-test showed that depression was significantly decreased in the experimental group between pre to post (p < 0.001) and mid to post (p < 0.01). Additionally, depression was significantly decreased in the control group between pre to mid (p < 0.05).

4. Discussion

The psychological well-being of elite shooters has a direct impact on their performance and competitive outcomes [20]. Stress, in general, is defined as a state of physical and psychological tension that arises in response to challenging or maladaptive situations, often manifesting through reactions to external stimuli, contingencies, and performance-related demands in competitive settings [21]. Such stress elicits negative emotional, physiological, and behavioral responses, including alterations in endocrine function [22]. It also influences the central nervous system and is associated with various neurophysiological changes, including heightened arousal, cognitive and behavioral shifts, and increased muscle tone [16,23]. In a context comparable to the present study, prior research on recovery following cycling exercise indicated that bilateral vagus nerve stimulation was associated with a significant reduction in stress-related pain and fatigue over a 4-day intervention period [8]. Consistent with these findings, the current study demonstrated that the experimental group receiving vagus nerve stimulation exhibited a significant reduction in stress levels compared with the control group. These results suggest that vagus nerve stimulation may positively influence athletic performance by alleviating stress in shooters affected by psychological strain [24]. In addition to reducing stress, vagus nerve stimulation significantly improved competitive state anxiety in the experimental group, including reductions in cognitive and somatic anxiety and enhancements in self-reported confidence. Previous work by Yoon demonstrated that noninvasive vagus nerve stimulation modulates autonomic nervous system activity and provides relief from emotional anxiety and stress [25]. Given the involvement of vagus nerve stimulation in the regulation of mood states [26], the observed reductions in competitive anxiety in the current study may reflect its stabilizing influence on affective processing, which may, in turn, benefit athletic performance. Furthermore, vagus nerve stimulation led to a marked increase in confidence among the participants. In athletic contexts, confidence is defined as the belief in one’s capacity to perform successfully under pressure [27]. Supporting these results, a prior study involving individuals with epilepsy found that vagus nerve stimulation increased the proportion of words recalled with confidence, relative to a control group [28]. These findings suggest that vagus nerve stimulation can enhance cognitive self-assurance, a factor that may contribute meaningfully to performance outcomes. Finally, the present study observed a significant reduction in depressive symptoms among shooters who received vagus nerve stimulation. Previous studies have reported that vagus nerve stimulation affects brain regions responsible for mood regulation and can alleviate symptoms of mood disorders, particularly depression [29]. Additionally, a 10-week intervention study found that vagus nerve stimulation not only improved mood, but also appeared to promote resistance to depressive symptoms [30]. Collectively, these results, along with prior evidence, support the potential of vagus nerve stimulation as an effective intervention for reducing stress and mitigating anxiety and depression in female elite shooters.

The vagus nerve transmits information via A, B, and C fibers, enabling a wide range of regulatory effects and physiological feedback mechanisms related to bodily states [31]. Early studies demonstrated that manual compression and transcutaneous electrical stimulation of the vagus nerve could reduce heart rate and suppress seizure activity, leading to investigations into its therapeutic potential for epilepsy [32]. Invasive vagus nerve stimulation is currently approved by the U.S. Food and Drug Administration as a treatment for refractory depression, and its psychological effects—particularly its antidepressant properties—have been well documented [33]. These effects are mediated, in part, by the activation of the striatum and raphe nucleus via transcutaneous vagus nerve stimulation, which promotes the release of key neurotransmitters such as norepinephrine and serotonin—both of which play essential roles in mood regulation [34]. In the present study, psychological changes were observed in elite shooters following transcutaneous, auricular-based vagus nerve stimulation, rather than invasive implantation. This noninvasive intervention led to significant improvements in stress, competitive state anxiety, and depression. These effects may be attributed to alterations in functional connectivity between the default mode network and emotion-regulating brain regions, as previously proposed in the literature [35]. Collectively, the findings support the conclusion that a 4-week course of transcutaneous vagus nerve stimulation effectively enhances psychological well-being in elite shooters.

Despite these promising results, several limitations of the present study warrant consideration. First, the small sample size restricted the statistical power and generalizability of the findings. Future studies should recruit larger cohorts and include male athletes to more comprehensively assess the effects of vagus nerve stimulation across different populations. Second, while the stimulation protocol was based on prior research, the optimal duration and frequency of vagus nerve stimulation remain to be empirically validated; subsequent research should aim to refine and optimize these parameters. Finally, the psychological outcomes in this study were assessed using self-reported questionnaires, which are inherently subjective. Future research should incorporate objective physiological and neurobiological measures to corroborate these findings.

5. Conclusions

The study highlighted that vagus nerve stimulation is effective in improving psychological state in shooters. Our findings demonstrate that 4 weeks of vagus nerve stimulation treatment significantly improved stress, cognitive anxiety, somatic anxiety, and depression and improved confidence in elite shooters. Psychological negativity can negatively impact a shooter’s mental health and performance and should be managed on an ongoing basis. Thus, 4-week treatment with vagus nerve stimulation can be a positive impact on mental health in elite shooters. Additionally, improving the mental health of shooters is expected to improve their performance.