Effectiveness of Neurofeedback and Transcranial Direct Current Stimulation on Reducing Competitive Anxiety in Volleyball Players: A Systematic Review

Elite-level (national) volleyball is associated with high psychological pressure and the constant need for rapid decision-making, which can affect cognitive performance and sports skills. Neurofeedback (NF) and transcranial direct current stimulation (tDCS) have been proposed as non-invasive interventions to enhance mental performance and reduce anxiety in athletes. This systematic review aimed to synthesize and compare the existing evidence on the effectiveness of these two methods in reducing competitive stress and anxiety in athletes, with a focus on the volleyball player population. This study was conducted according to the PRISMA guidelines, and a literature search was performed in PubMed, Scopus, Web of Science, Google Scholar, SID, and Magiran databases using keywords related to neurofeedback, tDCS, competitive anxiety, stress, sports performance, elite athletes, and volleyball, covering the period from 2010 to 2026. Clinical trials, quasi-experimental studies, and interventional studies examining the effect of NF or tDCS on psychological, physiological, or performance-related indices in athletes were included in the analysis, and the methodological quality of the studies was assessed using the Cochrane risk-of-bias tool. Ultimately, 18 studies (comprising 5 neurofeedback studies, 8 tDCS studies, and 5 stress/anxiety/biofeedback studies) were included, collectively involving 389 independent human participants; of these, 7 studies were conducted directly on volleyball players, 4 of which involved an active neurofeedback, tDCS, or multimodal biofeedback intervention, while the remaining evidence was drawn from other sports disciplines (such as track and field and soccer) or healthy non-athlete populations as supportive and mechanistic evidence. The included studies reported that neurofeedback was associated with reduced cognitive and somatic anxiety and increased competitive self-confidence (p≤0.002), including in one direct trial on elite and non-elite volleyball players that showed reduced negative self-talk and improved serve performance. tDCS was also reported to improve cognitive performance, reduce reaction time, and enhance athletic performance (p<0.05), including in professional volleyball players who experienced improved spike speed and consistency as well as reduced pre-competitive anxiety. Evidence also indicated that tDCS significantly improved attention, cognitive performance, mental fatigue, and reaction time (p=0.001). Furthermore, elevated pre-competition cortisol levels were reported to be associated with reduced offensive performance, and increased state anxiety was associated with decreased serve performance, particularly among female athletes. Evidence suggests that neurofeedback and tDCS, through distinct mechanisms, can reduce competitive anxiety in volleyball players; however, future research with larger samples and standardized protocols is warranted.