Transcranial direct current stimulation (tDCS) is a simple, portable, and low-cost technology applied in neuroscience for therapeutic purposes and neurophysiological research of brain activity. Enhancing the impacts of training and improving performance in athletes through the use of tDCS is a significant aim for today.

The primary purpose of this study is to determine how non-professional active athletes' balance and movement measurements can be affected by the simultaneous application of a 4-week balance training and anodal tDCS of motor cortex(M1). This study hypothesizes that anodal stimulation of motor cortex will enhance performance in balance training among moderately active and healthy participants. The study outcomes will provide data for literatures on performance enhancement by demonstrating how effective skill development can be acquired in a short time among moderately active athletes. In addition, the study outcomes will provide convenient tDCS parameter for future neuromodulation studies interested in the treatment of balance disorders in patients and the elderly. Uniquely, in our study, the link between tDCS and movement parameters will be investigated. Additionally, a long-term balance training program in combination with tDCS of M1 in amateur has never been tested in amateur athletes.

The secondary purpose of the study is to obtain feedback from participants via pre- and post-tDCS and balance training, using continuous performance tests, estimated reaction time, and depression-anxiety scales to gather data on reaction time, anticipation, impulsivity, attention, and mood changes that directly affect athlete performance. In continuous performance test, a decrease in reaction times without an increase in the number of errors (misstep-commission) and the number of non-pressing (non-pressing-omission) will be considered as a successful outcome. While increasing balance performance and reducing the reaction time is anticipated as a positive outcome, simultaneously changes in mood, attention, and error rate is an unanticipated and undesired outcome. Although the selected stimulation area is not directly related to these functions, this study will additionally control for any potential changes that might have been missed in functions that are not the study's primary focus.

Previous studies have demonstrated that the level of physical activity has an impact on response of tDCS application. While several studies found no tDCS effect on participants with both high and low levels of activity, it is expected to have greater impact on moderately active people. However, no study has yet investigated tDCS with moderately active athletes. Among studies investigating balance, only one study on healthy subjects has examined the correlation of tDCS implementation with kinematic parameters, and a correlation was found between increased balance performance and lower velocity parameter. By taking into account the effect of kinematic parameters on sports performance, this study intends to explore the effect of tDCS in greater detail by investigating both balance and movement analysis. This study will investigate the impact of combined anodal tDCS of motor cortex and 4-week balance-training program on static, dynamic balance and kinematic parameters in amateur athletes, and measure changes in reaction time and estimated reaction time. Previous studies showed that M1 anodal stimulation reduces reaction time, but estimated reaction time has never been examined. At the end of simultaneous tDCS-balance training, it is expected to reduce the reaction time without increasing the error rate and to achieve the expected reaction time, which is significant for improving athletes' performance.

Participants who met the requirements signed the informed consent form (BGOF) approved by the Ethics Committee and applied via the advertisements posted with permission from the university will be included in the study. Before the training and tDCS session, Beck Depression/ Anxiety Test and Dominant Foot Test will be applied to participants. Next, they will undergo a Continuous Performance Test (CPT) and an estimated reaction time test via a computer program and will last 5 minutes. CPT is a test performed to assess sustained attention and impulse control, where participants perform a task with a constant difficulty for several minutes. In addition, anthropometric measurements will be taken from the participants and these measures will be compared between sham and active groups to evaluate possible differences between two groups. After these tests, participants who are not suitable for the study will be eliminated, and remaining participants will be randomized into active or sham tDCS groups. Next, participants will attend a balance training session designed by a professional trainer to assess balance and movement parameters at the Koç University Movement Analysis Laboratory. The balance training program consists of a 5-minute warm-up and a 20-minute main section for the first and second weeks and a 5-minute warm-up and a 24-minute main section for the third and fourth weeks. The warm-up starts with a low-intensity cycling ergometer or low-intensity walking/running on a treadmill, followed by static/dynamic stretching exercises. During the 4-week balance training, the duration of a set is 30 seconds for the first two weeks and 45 seconds for the third and fourth weeks. Each exercise will be repeated twice on the right and left sides, totaling 4 repetitions. For some exercises, participants will perform them with their eyes open or closed, and on single or double legs. The tDCS device will be fixed on the participant's midline on their back and it will be constantly controlled during the training breaks and recharged if necessary. In case measurements cannot be taken due to a technical or scheduling issue, the same individuals will be recalled to the laboratory within the same week and they will be instructed not to engage in any extra training during that week.

At the end of 4-week combined balance training/ tDCS, participants will return to Movement Analysis Laboratory, and all tests performed at the beginning of study will be repeated. Individuals who miss two consecutive training sessions or a total of three training sessions in the 4-week program will be excluded from the study. To reduce the risk of this, participants will be provided with weekly schedules in advance. The next suitable participant identified through a pre-screening process will be included in place of those who are excluded from the study. Lastly, If the required number of participants cannot be reached during the initial interviews, the study announcement will be repeated and attempts will be made to recruit new participants. If sufficient participants cannot be provided from the Marmara University, amateur athletes who meet the research participant criteria will be sought outside of university.

Inclusion Criteria:

• Scoring below 19 on the Beck Depression Inventory
• Scoring 15 or below on the Beck Anxiety Scale
• Having no neurological, psychiatric, orthopedic, or inner ear-related diseases
• Not being a professional athlete in a branch involving balance training (e.g., gymnastics)
• Not using medication affecting the central nervous system
• Having not consumed alcohol at least 24 hours prior to the tests
• Having no metal implants or hip/knee prosthesis
• Not being pregnant

Exclusion Criteria:

• Scoring 19 or higher on the Beck Depression Inventory
• Scoring higher than 15 on Beck Anxiety Scale
• Being a professional athlete
• Using mediation affecting the central nervous system
• Alcohol consumption less than 24 hours prior to the test
• Having metal implants or hip/knee prosthesis
• Being pregnant