Non-Invasive Brain Stimulation Techniques and Effects on Neuromodulation and Athletic Performance in Combat Sports: A Systematic Review

Background: Non-invasive brain stimulation (NIBS), including transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), has emerged as a potential ergogenic strategy for modulating neural activity and enhancing cognitive and physical performance in sports. However, evidence regarding its application in combat sports remains limited, heterogeneous, and fragmented. This study aimed to systematically synthesize the effects of NIBS on neuromodulation and cognitive, physical, and psychophysiological performance-related outcomes in combat sport athletes. Although NIBS encompasses several stimulation techniques, the evidence identified in combat sport athletes in this review predominantly involved tDCS. Methods: A systematic review was conducted in accordance with the PRISMA 2020 guidelines and registered in PROSPERO (CRD420251150915). Searches were performed in CAPES, PubMed, Scopus, and SPORTDiscus using predefined keywords related to combat sports and brain stimulation techniques. Studies were included if they involved combat sport athletes and investigated the effects of NIBS on performance-related outcomes. Data extraction included study design, sample characteristics, stimulation protocols, and main findings. Methodological quality was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool for randomized studies and ROBINS-I for non-randomized studies, while certainty of evidence was evaluated using the GRADE framework. Results: Nine studies were included in the final synthesis (eight identified through database searching and one through other methods/manual reference screening), encompassing athletes from taekwondo, judo, boxing, mixed martial arts, fencing, and Brazilian jiu-jitsu. Most studies applied tDCS protocols targeting the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC), with intensities ranging from 1 to 2 mA and stimulation durations between 10 and 20 min. tDCS demonstrated potential benefits in reaction time, selective attention, memory, and resistance to fatigue, as reflected by increased time to task failure. Additionally, enhancements in neuromuscular activation and reductions in anxiety were observed. However, results were heterogeneous, and some studies reported no significant effects on performance-related variables. Risk-of-bias assessment revealed methodological limitations across studies, and GRADE indicated low-to-very-low certainty of evidence for most outcomes. Conclusions: tDCS may influence selected cognitive, neuromuscular, and fatigue-related outcomes in combat sport athletes; however, the direction and magnitude of these effects are inconsistent across studies. Given the substantial methodological heterogeneity and the low-to-very-low certainty of evidence, no definitive conclusions regarding efficacy or routine practical application can currently be drawn. Further large-scale, standardized, high-quality randomized controlled trials are needed.