Introduction

Successful athletes frequently tackle various challenging obstacles. Competition in sports may be perceived as a source of threat because, among other things, an athlete’s reputation is typically tied to how they perform, the outcome is never certain, and they are subject to criticism from the public and outside observers1,2. Prior to any sports competition, athletes mainly emphasize winning, which causes behavioral and emotional changes leading to pre-competitive anxiety (P.C.A.). Dread of failing and performance pressure results in a diminution of sports performance and altered quality of life3.

According to a meta-analysis, the rate of anxiety in the general population is about 10.6%–12% and in professional players, it is 8.6%, being more significantly associated with female, younger and less experienced athletes4. Among all students, it is more challenging for collegiate athletes, particularly as they undergo multiple physical and psychological transformations5. Collegiate athletes are most likely at risk of suffering from depression and have anorexia nervosa, sleeplessness, mood swings, substance misuse, sleeping difficulties, and suicidal thoughts6,7. Data suggest that in collegiate athletes, 48% of women and 31% of men suffer from anxiety and depression8. Although stress is subjective and individualized in nature the impact of negative feelings or distress cause tension, trouble concentrating, sweaty palms, sleep disturbances, irritability, and in some cases, appetite loss. The cumulative state of anxiety or stress may increase the risk of illness an injuries in an individual5. Cognitive symptoms, including uncertainty, anxiety, lack of focus, low self-esteem, rejection, obfuscation thoughts, dizziness, unable to compete, are often the consequences of pre competitive anxiety8. To overcome all these issues, AASP (Association for Applied Sports Psychology) focuses more on collegiate athletes’ mental status by introducing awareness programs, care for mental issues and pre-participating in mental health screening9. There is robust- evidence to aid the use of psychological therapies to lessen athletes’ pre-competitive anxiety. Sports psychologists assist and instruct athletes in overcoming these emotional components by employing time-consuming strategies like mindfulness-based interventions and psychological retraining10. However, non-invasive neuromodulation, such as Transcranial Direct Current Stimulation (tDCS), has proved to be a promising, safe and inexpensive intervention to treat various psychosomatic disorders such as focus, cognitive speed, and motor performance11,12,13,14.

With tDCS, a 2 mA low-intensity current is delivered over target brain regions via electrodes (both positive and negative), causing excitation and inhibition of the required size and cortical excitability to last for minutes to hours15. Garcia et al.16 explored the effectiveness of tDCS on college-going students to improve anxiety and cognition and found favourable results for the population, but the subjects were not athletes. A review also supports the findings by exploring the effect of tDCS in patients with anxiety. It concludes that tDCS can prove to be more beneficial if applied in conjunction with other cognitive therapies17. The results were also supported by a systematic review, analyzing the effects of tDCS on different aspects of psychological disorders where anxiety was one of them and found effective intervention for it18. Another R.C.T. also provides preliminary evidence that the tDCS is effective in improving executive functioning among the geriatric population19. It has also been established that the Dorsolateral Prefrontal cortex is responsible for various psychological aspects of a human being. The selection of the dorsolateral prefrontal cortex (DLPFC) as a target for improving cognition and anxiety stems from its pivotal role in executive functions, working memory, and emotion regulation. By stimulating this region, interventions aim to enhance cognitive abilities such as cognitive flexibility and decision-making while also modulating emotional responses and reducing anxiety symptoms. The DLPFC’s connectivity with other brain regions involved in cognition and emotion regulation further supports its suitability as a target for interventions seeking to address both cognitive function and anxiety levels12,13. A feasibility study was also found to be effective in reducing competitive anxiety among elite athletes using tDCS by stimulating DLPFC20.

The literature available exhibited and explored the use of tDCS in various psychological disorders, but its effect has yet to be determined among collegiate athletes. Hence, the current study intends to further investigate tDCS as a strategy for lowering anxiety and linked cognitive implications due to the limits of current treatments for anxiety, particularly treatments for the cognitive connection of anxiety. The study hypothesized that the tDCS reduces pre-competitive anxiety and improves cognitive performance in Collegiate Athletes.

Methods

Study design and participants

The study design was a single-centre, randomized controlled trial with patient blinding, parallel-group design. Nineteen healthy male and female collegiate athletes aged 18–25 years, all trained in volleyball, were randomly relocated 1:1 into experimental and control groups. The lottery method and SPSS software were used for randomization. Randomization was performed by an examiner not associated with the study, and the outcome assessor was kept blind to the allocation. The data was collected in March 2021, 10 days prior to a national-level inter-university sports competition. All participants’ BAI scores fell between moderate to severe anxiety at baseline. Players with psychological issues, injuries, fractures, cardiovascular diseases, neurological disorders, and musculoskeletal disorders were excluded. Ethical approval had been provided by the Institutional Ethical Committee (I.E.C.) of Maharishi Markandeshwar (Deemed to be University) (IEC/MMDU/2019/1530). It was taken in accordance with the revised 2013 Helsinki Declaration and National Ethical Guidelines for Biomedical Research Involving Human Participants, 2017. The study was registered on ctri.nic.in (registration number: CTRI/2020/06/025749 on 09/06/2020). The copyright of the intervention protocol of the study was done (registration number: L-100452/2021). All experiments were performed in accordance with relevant guidelines and regulations.

Sample size

The sample size was estimated using the G-power 3.1 version. The effect size was 1.2, and the power was 80%21. The calculated sample was 19 (Fig. 1). Transcranial direct current stimulation (tDCS) was independent variable22. Pre-competitive anxiety and cognitive performance were dependent variables.

Fig. 1
figure 1

The Consolidated Standards of Reporting Trials (CONSORT) flowchart shows the recruitment, randomization, and analysis of participants.

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The primary outcome measure was the Beck anxiety inventory scale (BAI), a 21-item scale containing signs of anxiety and a total score of 0–63. The reliability of internal consistency estimation was 0.90 or higher23.

Secondary outcome measures were the Stroop Color and Word test (SCWT), a three-item test in which the participant had to read the color of the word mentioned on a box. The test was done to evaluate the executive brain functions24, the Digit symbol substitute test (DSST), in which the participant received a sheet in which a 9-digit coding table was printed, with 0–9 digits having special symbols. The participants had to mark as many symbols they could make for a specific digit, counting the number of digits marked25. Biofeedback analysis, i.e. electromyography- (E.M.G. Biofeedback), was used before and after intervention to determine changes in muscle tension. In this study for E.M.G. biofeedback, the frontalis muscle, which is greatly influenced by psychological changes, was targeted26.

For evaluation purposes, lab setting, electrodes, battery, saline water and tDCS were required.

Intervention

Group A (experimental group)

The participant was positioned in a high setting, and the therapist stood behind the subject. A portable stimulator manufactured by Walnut Medical in India produced a 2 mA direct current. This current was applied through a pair of electrodes measuring 5 × 7 cm. The anodal electrode, enveloped in saline-soaked sponges and coated with conductive paste (Ten20®, Weaver and Company, Aurora, CO), was positioned over the left DLPFC at F3, following the international 10–20 electrode placement system. To prevent polarization of other brain regions, the cathodal reference electrode was affixed to the right supraorbital region. Stimulation commenced 2 min before participants began the PASAT, gradually increasing over 5 s. During the anodal stimulation session, a continuous current of 1 mA was administered for 20 min until task completion, followed by a 5-s fade-out. In the sham condition, the current was applied for only 30 s before gradually decreasing over 5 s. The device maintained the impedance levels below 10 kΩ. It is the safe mode of placement using C3 and C4 locations over the required area by maintaining proper electrical field distribution of current. The intervention continued for ten consecutive days with a constant current of 2 mA for 20 min for each session22. The participant was blinded for the stimulation process.

Group B (control group)

In the control group, participants received a placebo effect or sham tDCS, which was given by placing electrodes in the same areas of the brain as placed in the experimental group. However, in the control group, after 30 s, the stimulation was stopped with placement for 20 min in each session. The participant was blinded for the stimulation process22.

Data management

An independent observer assessed baseline and treatment assessment data. Participants did not report adverse effects during or after the intervention.

Statistical analysis

SPSS Version 20.0 was used at a 0.05 level of significance to analyze the data. The Shapiro–Wilk test confirmed the normal distribution of the data. The baseline demographic characteristics and outcome measures of participants were compared inter-group using the independent sample t-test and reported as mean and standard deviation (mean ± S.D.). A parametric paired t-test was used for intra-group comparisons, and an independent sample t-test was used for the intergroup analysis of continuous variables (SCWT, DSST and E.M.G. Biofeedback). In the study, the BAI was ordinal for which the Wilcoxon signed-rank test was used within the group. The Mann–Whitney U test was used for between-group analyses, and a significance level of p < 0.05 was used.

Results

Participants

Shapiro–Wilk normality test established that the characteristics of participants followed a normal distribution (p > 0.05) except for age in the experimental group (p = 0.003). Demographic details and baseline outcome measures of Group 1 (experimental group) and Group 2 (control group) had no statistically significant difference (Table 1).

Table 1 The baseline characteristics of study participants in the experimental and control groups and the results of the Shapiro–Wilk normality test.
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In the post-treatment session, the intergroup analysis revealed that the participants’ final values of primary outcome BAI in the experimental group were statistically significantly lower than the control group’s final values (z = − 2.89, p < 0.05). Secondary outcome variables’ (Stroop test, DSST and EMG-time relaxed) final values in the experimental group were statistically higher significantly than the control group’s final values at the end of treatment (p < 0.05) (Table 2).

Table 2 Inter-group analysis of variable measurements among participants at the end of treatment.
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Intra-group analysis revealed that the final values of primary outcome BAI in the experimental group were statistically significantly lower than initial values (z = − 2.21, p < 0.05). Stroop test, DSST and EMG-time relaxed variables’ final values were significantly higher than the initial values in the experimental group (p < 0.001). In the control group, the final values of the secondary outcome (Stroop test) were significantly higher than the initial values statistically (p < 0.01) (Table 3).

Table 3 Intra-group analysis of variable measurements among participants between the baseline and final treatment values.
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Discussion

The study determined the effect of several tDCS montages on pre-competitive anxiety and cognitive performance in collegiate athletes aged 18–25 years. Although the age range was small for the study yet this age range has been supported by previous literature wherein the mean age group for the collegiate athletes was evaluated as 19.6 ± 1.3 years27, a systematic review which included 21 articles, out of 11 articles described the mean age of collegiate athletes was 20 years8. Another retrospective cohort across 15 nations analyzed the age and support services for athletes and estimated the mean age to be around 18 years, which further supports the study28. The current findings confirmed that treatment with tDCS significantly helped to reduce the severity of anxiety among collegiate athletes (Tables 2 and 3). The BAI was used to evaluate subjective symptoms of anxiety and its severity. The participants reported moderate to severe levels of anxiety at baseline and were randomly relocated to experimental and control groups using block randomization. In the post-treatment session, the within-group analysis of BAI in the control group showed no statistically significant difference (Table 2). In the experimental group, post-tDCS sessions for ten consecutive days, participants reported a low level of anxiety. It showed a statistically significant difference (p value < 0.05) between initial and final values (Table 2). The analyses of the final values of BAI between the groups revealed significant differences between the experimental and control groups (p value is 0.004) (Table 3). The level of anxiety falls under the normal levels in the experimental group following the intervention. The optimum level of stress among players before competition is vital for their peak performances. Mohammad Javad et al. performed a study to investigate the tDCS effect on post-traumatic stress disorder and found significantly favourable results29. Cognition plays an important role in decision-making, concentration and working memory. Cognitive performance has a subcategory known as executive functioning, which comprises the action plan, problem dealing, and executive functioning, which was evaluated using the SCWT and DSST. The SCWT was used to measure inhibitory control. The test was performed in 3 sub-tests with a time limit of 45 s for each sub-test.

The SCWT showed significant improvement in the experiment group post-treatment session (Table 2). Between-group analysis also showed significantly higher values in the experimental group (p value = 0.01) (Table 3). Previous studies suggest that tDCS over the dorsolateral prefrontal cortex improves cognitive functions by enhancing goal-oriented processes and executive function. It also shows improvement in athletes with depression when placed in the DLPFC area30. tDCS stimulation improved working memory as well as long-term memory when placed over the motor cortex, modulating receptor-like NMDA and synaptic plasticity to improve long-term memory31. For anxiety disorders, cognitive-behavioral therapies are frequently advised. These therapies, which are often given in 10 to 12 sessions spread over several months, have significant challenges with regard to adherence and compliance.

DSST was used for processing memory and speed, with the experimental group showing significant differences within the group with a large effect size and acceptable power of the study. The control groups revealed no significant difference between initial and final values (Table 2). The between-group result shows significantly higher values in the experiment group (p = 0.001) as compared to the control group’s final values (Table 3). The supported study suggested DSST as an important coding test component used for mild cognitive impairment32.

In this study, muscle tension and anxiety were also noticed with the help of biofeedback electromyography. The muscle tension was assessed using electromyography; the tensed time was screened within 20 min. The experimental group showed significantly higher relaxed time post-treatment session compared to initial values (Table 2). The between-group analysis showed significantly higher relaxed time in the experimental group as compared to the control group post-treatment (Table 3). The reason behind the increased relaxed time value in the control group can be familiarity with the device or procedure. Participants were more comfortable and relaxed during the process. Other studies suggest that biofeedback works on physiological and biomechanical aspects; the muscle activity screened by electromyography is the popular method used for anxiety, stress, headache and pain. Michael Reed et al. stated that E.M.G. biofeedback effect on test and general anxiety when placed over the forehead for a session of 2 per week for four weeks showed significant changes in the level of anxiety33.

The study’s findings affirm that Transcranial Direct Current Stimulation (tDCS) effectively reduces anxiety among collegiate athletes, in line with existing literature on tDCS’s efficacy in anxiety and cognition management. The notable decrease in anxiety levels, reflected by significant changes in Beck Anxiety Inventory (BAI) scores (p < 0.05), underscores tDCS’s potential as a non-invasive and cost-effective therapeutic tool in sports psychology. This study’s focus on collegiate athletes addresses a research gap, demonstrating tDCS’s ability to alleviate pre-competitive anxiety in a population navigating unique academic and athletic stresses. Insights into tDCS’s mechanisms, targeting the dorsolateral prefrontal cortex (DLPFC) to modulate cognitive and emotional processes, align with prior findings showing DLPFC stimulation enhances executive functions and reduces anxiety symptoms12,13,20. Implications include integrating tDCS into athlete training to optimize performance by reducing anxiety and enhancing cognitive focus, particularly in high-pressure competitions. Moreover, tDCS may extend its benefits beyond anxiety management to enhance critical cognitive functions like decision-making and reaction times, offering promising applications in sports psychology. These findings contribute to the broader field of neuromodulation, endorsing the use of non-invasive brain stimulation techniques like tDCS to address psychological conditions across diverse populations, including young adults managing academic and athletic pressures.

The Minimal Clinically Important Difference (MCID) for the Beck Anxiety Scale was determined in the present study, and the score was 4.06. MCID = minimal important difference (MDC) × 1; (MDC = standard error of measurement (SEM) × √2 × 1.96 for a 95% Confidence interval; SEM = SDpooled √1 − r; SDpooled = √(SD1)2 + (SD2)2. Hence, the Beck Anxiety Inventory was statistically as well as clinically significant. tDCS intervention time is less and can be easily used prior to sports competitions. It is a safe and non-invasive technique that is easily available in sports setups or universities’ sports labs nowadays. The study focuses on the important factors, i.e. anxiety and cognitive performance, which are mostly neglected during the training period. The tDCS should be used as a pre-participating preparatory device as it not only shows an effect on stress or anxiety but also focuses on behavioural changes by mood uplifting. It enhances athletic performance and can also help reduce pain, depending on the area of placement. The tDCS can also be used to treat other neurological conditions affecting sports performance, such as depression, stress and fear. It enhances athletes’ performance and can also help reduce pain, depending on the area of placement.

Although the sample size was less, the power of the study shows significant results. The power for the primary outcome was 99% (calculated through G-power software). The effect size was calculated for secondary outcomes using Cohen’d intergroup analysis (meanexperimental group–meancontrol group/SDpooled) and showed a large effect size in the Stroop test (1.79) and DSST test (0.56) and a medium effect size in E.M.G. (0.46) hence establishing the practical significance of results.

Limitations of the study: The study encounters several methodological limitations that warrant acknowledgment. Firstly, the small sample size, largely attributed to pandemic-related lockdown measures, restricted participant recruitment, thus compromising the statistical power of the investigation. Consequently, the generalizability of the findings may be constrained, as the sample might not adequately represent the broader collegiate athlete population. Additionally, the narrow age range of 18–25 years further limits the applicability of the results to older athletes. Moreover, the imbalanced dropout rates among female athletes skewed the gender distribution, potentially introducing bias and undermining the robustness of gender-specific analyses. Furthermore, the relatively brief duration of the study may fail to capture the enduring effects of the intervention, necessitating protracted follow-up periods to accurately assess sustained outcomes. These methodological constraints underscore the importance of prudently interpreting the findings and highlight avenues for future investigations to address these limitations and advance our comprehension of anxiety management in collegiate athletes.

Future recommendations of the study

Future research endeavors should prioritize larger, more diverse samples and implement strategies to mitigate dropout rates to bolster the study’s external validity and generalizability. It would be beneficial to extend similar studies to higher levels of competition, such as state and national-level tournaments involving professional athletes. Extending the age limit to include middle-aged athletes would broaden the study’s applicability. Moreover, recruiting a higher proportion of female athletes would address potential gender disparities in anxiety and treatment response, ensuring the intervention’s effectiveness across genders. Furthermore, incorporating a longer follow-up period in future studies would provide more comprehensive evidence of the intervention’s long-term effectiveness and sustainability, offering valuable insights into its lasting impact on anxiety management in athletes.

Conclusion

Transcranial direct current stimulation (tDCS) can be used as a pre-participating preparatory device as it is clinically and statistically significant in reducing pre-competitive anxiety from moderate to low levels. It is also focused on behavioral changes by uplifting mood. It can be used in sports rehabilitation centers or university sports labs.