Transcranial Direct Current Stimulation and Cranial Electrotherapy Stimulation in Athletes: Optimizing Athletic Performance and Sleep Quality Through Neuromodulation.

Neuromodulation is a procedure relying on the delivery of specific stimuli to selected sites of the nervous system and hereby influencing its activity. Even though the underlying neurobiological mechanisms are not yet fully elucidated and the research is still ongoing, neuromodulation is already being used as an intervention for various mental conditions and insomnia, or it may even improve the physical performance of athletes. This narrative review summarizes current evidence on the effects of specific neuromodulation techniques on performance and sleep quality in athletes, focusing on cranial electrotherapy stimulation (CES) and transcranial direct current stimulation (tDCS). PubMed, SCOPUS, Web of Science and Ovid MEDLINE databases were searched for relevant articles. All types of publications were taken into account, but original studies, randomized controlled trials (RCTs), and meta-analyses were given priority. Current evidence shows that while tDCS may improve athletic performance, especially endurance and sport-specific skills, its impact on sleep in athletes is inconclusive. This method may increase subjectively reported total sleep time and subjective sleep quality, but no objective improvement has been demonstrated. CES findings are preliminary: evidence from the small trials suggests improvement of selected objective sleep parameters, but the evidence base is limited to two small studies, one of which lacked a sham condition. In conclusion, non-invasive neuromodulation methods, specifically tDCS and CES, may impact athletic performance and help treat sleep disorders in athletes. Neuromodulation should not be viewed as a standalone method, but rather a complementary tool to other known interventions for insomnia in athletes. Although the aforementioned techniques show promising results, the research on this topic is limited and requires further evaluation.