Table 3.

Materials, methods and results of biofeedback training studies.

Authors and Type of Article	Experimental Group	Control Group	Neurofeedback Training	Results	Conclusions
Authors, Countries of Stud, Study Type	Gender, Age, Sample Size, Sports	Gender, Age, Sample Size, Sports	Methods, Type of Training, Protocol, Frequency of Training	Performance Level, Outcomes	Was the Training Used Effectively and How Will It Affect the Athletes?
Nika Pusenjak et al. [14], Slovenia, clinical study, a practitioner’s perspective	18 professional athletes; 4 women 14 men 16–34 years Mixed sports (archery, shooting, fencing, wake-boarding, track-and-field, volleyball, basketball, skiing, cross-country skiing, swimming, tennis, cycling, taekwondo, table tennis, carting	21 professional athletes; 4 women 17 men 16–34 years Mixed sports (archery, shooting, fencing, wake-boarding, track-and-field, volleyball, basketball, skiing, cross-country skiing, swimming, tennis, cycling, taekwondo, table tennis, carting)	BioTrace software was used in the study, which is part of the Nexus 10 (Mind Media BV, NL) biofeedback device. Parameters studied: number of breaths per minute, heart rate, blood volume and coherence, galvanic skin response (GSR) and temperature. Two tests were conducted for each subject: a short stress test (5 min) and a long stress test (14 min) for both groups. Then neurofeedback training was conducted for 1 h 2x a week for 8 weeks for the experimental group using the Wild Divine biofeedback device and the Wisdom Quest integrated software. After the training cycle, both groups were re-tested.	The researchers showed that athletes who were able to achieve psychophysiological control could achieve a state of deeper relaxation, as indicated by improved breaths per minute, lower skin conductance, lower heart rate, higher blood flow and higher breathing, as well as heart rate coherence. More athletes in the experimental group were able to control individual parameters, as opposed to the control group. Only 5% of the subjects could train heart rate control in the face of a stressful stimulus. The main difference between the 2 groups concerned the skin conductance parameter. For the short stress test, the difference in change was more than two-fold (67% to 35%). Summing all parameters, the experimental group was better by >15%.	The researchers did not base their analysis on qeeg diagnostics; however, parameters related to stress response were analysed. In order to improve the quality of the study, it would be worthwhile to continue research among a larger group of subjects and supplement it with qeeg diagnostics and brainwave recording. The studied parameters, with the exception of GSR, were inconsistent in the experimental group and it is difficult to assess the effect of training on them. In future studies, other measurement parameters should be used to assess the effect of training, but GSR shows that the neurofeedback training used in this study allowed the subjects to better control stress and psychophysiological functions in the tests used.
Camille Jeunet et al. [15], France, clinical study	17 professional athletes (1 was excluded from analysis of the results because there were problems during the EEG recording) 15 males 2 females Age 21.4 ± 5.3 years Football goalkeepers	There was no control group in the study	Two sessions were conducted, each lasting 1 h, both in the same week. Four CVSA (covert visual spatial attention) tasks were performed, and EEG activity was recorded. Failed trials were not recorded for EEG analysis. EEG data were recorded using 2 g.USBAmp amplifiers (g.tec, Austria), using 32 wet (g. tec LadyBird) scalp electrodes (F3, F1, F2, F4, FC3, FCz, FC4, C1, Cz, C2, CP5, CP3, CPz, CP4, CP6, P7, P5, P3, P1, Pz, P2, P4, P6, P8, PO7, PO3, POz, PO4, PO8, O1, Oz, O2, 10–20 system), referenced to the right ear and grounded to AFz. The α-wave band (8–14 Hz) in areas of the occipital cortex was analysed. EEG data were sampled at 512 Hz. Data were recorded using OpenViBE45 software and pre-processed using MATLAB/EEGLab 4. The study took place under conditions of isolated distance from the screen, with each subject holding their chin in a holder. The Eye Tribe eye tracker was used at a distance of 40 cm from the subject at a frequency of 60 Hz, and a 1.5° gaze deviation of visual angle from the fixation point was tolerated. In addition, the multiple object tracking (MOT) test was performed during both sessions to assess intra-session improvement. MOT exercise was implemented in Unity 5.0 using the C# language. The covert attention task was implemented in C++ as the OpenVibe45 scenario.	Athletes with improved CVSA scores also had improved MOT scores. There was no correlation between knowledge and CVSA ability in athletes.	The results of the study indicate that the use of neurofeedback training may have an effect on CVSA in goalkeepers, which may translate into athletic ability; however, this study does not allow prove the statement, it only provides the potential for its continuation. The authors highlight the shortcomings of their study and the need to work with a larger group, over a longer period of time, and using a control group. Two sessions are not enough to see clear changes in athletes’ form. Improvements in the MOT test (pre vs. post) ranged from −9.17% to 19.17%, demonstrating the potential of this type of training in athletes and its effect on CVSA.
Magdalena Krawczyk et al. [24], Poland, clinical study	6 professional sportspersons from the National Team of the Polish Judo Association 6 men 22–25 years old Random selection	6 professional sportsmen from the National Team of the Polish Judo Association 6 men 22–25 years old Random selection	A series of 15 therapy sessions was conducted for the experimental group, after which the authors introduced a break under a modified Michael Thompson Training, who is the author of the basic concept of applied psychophysiology. Each was preceded by a 3 min EEG diagnosis using a single-channel lead, and reference leads are also needed. Diagnostics were performed with eyes open and closed and with an activation task. During the task, the reference electrode was attached to the left ear, the ground electrode to the right ear, and the active electrode to the Cz point, while the active electrode was repositioned to the C3 point during training. The signals were filtered within the range of 2–40 Hz. Periods without artifacts were analysed. The testing protocol followed was beta1/theta, which is used to increase concentration and narrow the attention of the athletes. The control group underwent the same training procedure. EEG simulation was displayed independent of the subject’s wave patterns instead of the difference regarding the implementation of the beta1/theta protocol. The study was carried out with the Biograph Infiniti 6.0 and using the ProComp 5 decoding device, which was equipped with a 5-channel lead and an EEG sensor. The prerequisite for starting the EEG diagnosis was an impedance below 5 kΩ, and the measurement between the electrodes had to be greater than 1 kΩ. Respondents were advised to refrain from using medications and stimulants 12 h before each training session and test. Visual reaction speed was tested by a computer system using the Vienna Test System (WST).	Data taken for interpretation in the control group after the first and second cycles of testing for the group showed no statistically significant changes. In contrast, in the experimental group, a significant linear decrease in theta waves and an increase in beta waves were observed after the first and second training cycles.	Neurofeedback training caused significant changes in the preparation of athletes for sports competitions. In studies, it has been reported that the greatest therapeutic effects, in terms of reaction time training, were achieved between the fourth and fifth weeks of training. The study was conducted among a fairly small group of athletes, but it was a homogeneous group with similar ages, representing similar levels of training. The applied EEG diagnostics allowed for more precise results and improved the quality of evidence from the study. The authors themselves pointed out that there is little research on the changes in EEG wave dynamics in relation to individual training sessions. Neurofeedback training has measurable benefits; however, the methodology for conducting the training is still unsystematic and needs to be further explored.
Fatemehsadat Hosseini et al. [25], clinical study	15 elite and 15 non-elite volleyball players		Neurofeedback training was based on increasing the amplitude of the sensory motor band. Volleyball players’ EEG recordings were collected using the ProComp Infiniti. One training session lasting 30–45 min.		Increase in serving efficiency after neurofeedback training, especially volleyball players from elite groups.
Mikicin Mirosław et al. [26], clinical study	17 students of the Military University of Technology, who are professional soldiers and attend additional shooting classes	10 students of the Military University of Technology, who are professional soldiers and attend additional shooting classes	In both groups, the aim was to strengthen the beta frequency. In the experimental group, the subjects received positive or negative feedback only on the computer screen. In the control group, feedback was unrelated to the actual actions of the subjects. The training was provided using the EEG DigiTrack Biofeedback system. The average testing period was about 90 min, and 1 neurofeedback training session lasted about 40 min, in 20 sessions which took place 1–2 times a week.		For professional soldiers, level of attention and arousal are important skills. Both improved significantly in the experimental and control groups.
Cheraplina Larisa [27], clinical study	321 persons from different sports, elite athletes		At first, the “background” cerebrum bioelectric activity of all examined persons (n = 321) was registered in trials with open and closed eyes, with a following analysis of absolute and relative power in frequency bands of theta (4–8 Hz), alpha (8–13 Hz) and beta (13–20 Hz) activity. A second-stage neurofeedback course was directed towards increasing EEG power in the alpha-band via Pogoda Eva’s methodology. At the first stage, the duration of each trial was 5 min. During the second stage, 217 sportspersons had a 15-day neurofeedback course. The sessions were held once a day, continuing for 25–30 min.		The conducted research allowed concluding that the revealed changes in the sportsmens’ EEG depend on the kinematic characteristics of executed movements, sport skill and sex. These factors influence neurofeedback success but only in aggregation.
Mikicin Mirosław et al. [28], clinical study	7 elite swimmers		The athletes participated in the pre-test (Test 1), followed by the Neurofeedback training sessions (on a swimming ergometer), and the pre-test was performed after completion of all the sessions (Test 2). The following characteristics were measured in Test 1 and Test 2: anthropometric indices and body composition. Additional tests were performed: Kraepelin test, Holter EEG and EMG during 10 min of physical exercise, Progressive Test and the Wingate Test. Each exercise was performed on different days in the morning. Training sessions for 4 months. The study participants performed 20 neurofeedback training sessions (every 7 days, on average) using a swimming ergometer, with a continuation of conventional swimming training.		Neurofeedback-EEG training had an effect on the optimisation of psychomotor activities. Neurofeedback training during physical exercise may suggest the tendency towards maintaining energy and consistency in action.
Mikicin Mirosław et al. [29], clinical study	25 athletes (15 males and 10 females), student athletes involved in swimming, fencing, track-and-field, taekwondo, judo	10 athletes (5 males and 5 females)	Training consists of autogenic, audio–visual relaxation with eyes closed after everyday athletic training (in home conditions). The EEG examination (in resting supine position with eyes open and closed), attention reaction test and addition test for evaluation of Kraepelin’s work curve were carried out on each subject at the beginning and the end of the NFB training. The experimental group participated in 20 sessions of neurofeedback training for 4 months (every 7 days, on average). The control group performed regular sport training for 4 to 7 months between EEG recordings, similarly to sportspersons from the experimental group, but without parallel neurofeedback training and relaxation sessions.		The visual–neurofeedback training and audio–visual alpha relaxation training constitute holistic assistance in athletic training. They produce changes manifested in functionally different, eyes-open and eyes-closed states of the brain.
Maszczyk Adam et al. [30], clinical study	6 male athletes from the National Team of the Polish Judo Association	6 male athletes from the National Team of the Polish Judo Association	The NFB training protocol was performed and recorded using the Deymed Truscan system with 24 active channels. The effect of NFB training was examined by computer-based simple and complex reaction tests and selected tests of the Vienna Test System (VST). The research was carried out in 2 cycles. The first cycle included 15 training sessions held every other day. The duration of a training session was 10 min. The second part of the research, which took place after a 4-week interval, was characterised by the same frequency of training sessions, but at a reduced duration (4 min).		There were statistically significant differences between the control and experimental groups in the results of reaction speed tests after individual cycles of training. the influence of the frequency and duration of training on the result is demonstrated.
Balconi Michela et al. [31], clinical study	50 Italian subjects with valid driver’s licences participated in the study (38 females, 12 males)		Pre- and post-treatment assessment included behavioural, psychometric, neuropsychological and psychophysiological autonomic measures. The Driver Behavior Questionnaire (DBQ) and the Active Box (AB) device were used to evaluate everyday driving behaviour. Lasting 21 days and including daily sessions for practice (gradually incremented duration: from 10 min a day to 20 min per day).		The results allowed to underline improvement in driving behaviour performance and a decrease in behind-the-wheel violations among the experimental group. They displayed a physiological, behavioural and neuropsychological increase in efficiency related to attention, as well as a driving-related behavioural improvement after NF training.