Enhancing autonomic regulation and attention through galvanic skin response and peripheral temperature biofeedback in female volleyball players: a randomized pilot trial

Abstract

Background

Biofeedback (BFB) is widely used to manage stress and anxiety in competitive athletes; however, its effects on cognitive domains such as attention remain underexplored. This study aimed to evaluate the impact of a multimodal BFB intervention on autonomic function and sustained attention in female volleyball players.

Methods

Twelve national-level female volleyball players were recruited and randomly assigned to either a BFB group (n = 6; M_age: 17.83 ± 0.75 years) or a control group (CG, n = 6; M_age: 17.67 ± 0.52 years) in this randomized pilot trial. The BFB group completed 15 sessions of multimodal BFB training over five weeks, while the CG received no intervention. Autonomic parameters, including galvanic skin response (GSR) and peripheral temperature (PT), were measured before and after the intervention using a BFB device. Sustained attention was assessed using the d2 attention test.

Results

ANCOVA results revealed significant improvements in PT (p = 0.020, η² = 0.673) and error percentage on the d2 attention test (p = 0.045, η² = 0.346) for the BFB group compared to the CG. Significant changes were observed in GSR, PT, and d2 attention test parameters from pre- to post- intervention following 15 sessions of BFB training in the BFB group (p < 0.05). No significant changes were observed in the CG (p > 0.05).

Conclusion

These preliminary results suggest that a 5-week multimodal BFB (GSR and PT focused) intervention may improve autonomic functions and cognitive performance in competitive female athletes. Further research with larger samples and diverse athletic populations is warranted to support or refute these findings and assess their generalizability.

Trial registration number

The study protocol was retrospectively registered at ClinicalTrials.gov (Registration No: NCT07061834) on 01/07/2025. Ethical approval was obtained from the Clinical Research Ethics Committee of Karamanoğlu Mehmetbey University prior to study initiation (Approval No: 02-2024/26; Date: 23/01/2024).

Introduction

The optimal performance of elite athletes represents the pinnacle of their developmental journey, encompassing both the prevention of performance decline and the maintenance of peak achievement levels [1]. In competitive environments, psychological preparedness is just as vital as physical conditioning for maximizing athletic output [2]. Stress triggers a range of psychophysiological responses, such as cognitive disruption, skin reactions, lowered body temperature, and hormonal imbalances, which frequently contribute to competitive anxiety [3]. Consequently, effectively managing competition-related anxiety is essential for athletes to perform with confidence and composure under pressure [4]. Sports psychologists play a key role in cultivating these mental skills to support enhanced performance. Nonetheless, the relationship between competitive anxiety and cognitive function is intricate and bidirectional, influencing aspects such as atten- tional focus, executive functioning, and perceptual-motor coordination [5, 6]. Previous studies have highlighted the dynamic interplay between anxiety and cognitive performance, particularly attention, in athletes facing competitive challenges [7, 8].

Cognition plays a vital role in shaping the performance of elite athletes by influencing decision-making, emotional regulation, and preparation both before and during competition [9]. The continuity of cognitive function, which includes an individual’s awareness of internal and external stimuli, as well as their perception and reasoning abilities, is closely connected to attention [10]. In sport psychology, achieving a state of full concentration on a task involves sustaining performance by filtering out irrelevant information [11]. Moreover, Zhu et al. [12] demonstrated that mindfulness-based practices, as part of applied sports psychology, lead to acute improvements in cognitive abilities among soccer players. Although applied sport psychology interventions targeting cognitive skills can enhance athlete performance and play a significant role in their success, their effectiveness depends on factors such as the type of intervention, athlete characteristics, sport context, and methods of implementation [13]. Therefore, there is a clear need for further comprehensive research to better understand and optimize these interventions across different athletic contexts and individual needs.

Contemporary sporting success increasingly depends on intricate details, leading to a rise in applied sports psychology [14]. This field emphasizes using physiological variables from computer-assisted tools to assess improvements in stress and anxiety [8, 15, 16]. as well as cognitive functions [17]. Biofeedback (BFB), a preferred tool for these assessments, provides a non-invasive method for evaluating quantifiable physiological traits such as heart rate variability (HRV) [18]. Although research often focuses on the effects of HRV-BFB interventions on psychological state and cognitive function, BFB can also be derived from other psychophysiological metrics, including galvanic skin response (GSR), peripheral temperature (PT), surface electromyography (sEMG), respiratory exchange ratio, and brainwaves [19]. These metrics contribute to improved emotional regulation and facilitate autonomic control of physiological responses, which are crucial for effective stress management [20]. BFB interventions enable individuals to learn to regulate previously unconscious physiological parameters, fostering the development of new patterns in physiological function and behavior [21]. By targeting various physiological mechanisms of stress (i.e., HRV, GSR, PT, and EMG) through a multimodal approach, BFB enhances self-awareness and provides deliberate control over typically involuntary physiological processes [22].

HRV-BFB model interventions have proven effective in improving anxiety and stress management among both trained individuals and athletes, establishing them as valuable tools for monitoring autonomic functions [2, 8, 18]. Additionally, Nashiro et al. [17] demonstrated that a 5-week HRV-BFB intervention positively impacts cognitive functions across a wide age range (18–80 years), suggesting that longer intervention periods may provide more comprehensive data. Other BFB models and psychophysiological parameters, such as GSR and PT, are effective in managing stress and improving self-regulation of the sympathetic nervous system [23]. Therefore, it is crucial to further investigate the potential impact of autonomic control-based BFB interventions on cognitive performance, given the established link between cardiac activity and cognitive attention [24]. Meanwhile, pre-competitive state anxiety, a psychological trait, significantly influences competitive sports performance and is linked to physiological responses of the autonomic nervous system [25]. Mental flexibility, which involves the ability to shift focus and switch between tasks with varying cognitive demands, is aptly described by the concept of alternating attention. Consequently, tailoring these BFB interventions to sport-specific contexts is essential to maximize their effectiveness and relevance for athletes.

In team sports such as volleyball, high-level performance depends not only on individual skills and team coordination but also on cognitive abilities, including sustained attention and the capacity to make rapid, accurate decisions under pressure [26]. Sustained attention, the ability to maintain continuous focus over time while filtering out irrelevant stimuli, is crucial in the fast-paced and unpredictable environment of competitive matches. Strong attentional control has been associated with more effective anticipation, faster reaction times, and improved tactical decision-making, particularly during critical phases of play such as serve reception, defensive transitions, and reading opponents’ actions [10, 11]. In sports settings, a recent study found that ten sessions of multimodal BFB effectively enhance physiological, psychological, and cognitive functioning in international tennis players [27]. This suggests that a multimodal BFB approach can be tailored to meet a sport’s distinctive cognitive and physiological demands by targeting the most relevant parameters, thereby helping athletes regulate both cognitive and physiological states and enhancing readiness and overall performance. Moreover, BFB may help volleyball players specifically manage in-game psychological stressors, such as competition anxiety, pressure during decisive plays, or shifts in match momentum. By providing real-time feedback on physiological states, athletes can learn to regulate arousal, maintain composure under pressure, and sustain optimal cognitive functioning during critical phases of play, thereby supporting both individual and team performance [28]. Despite these promising points, there remains a lack of research on the effectiveness of BFB in enhancing cognitive skills for elite athletes and providing a clear competitive advantage across various team sports.

The current study

Given the intricate interplay between cognitive function, anxiety, and physiological regulation in elite athletes, it is crucial to explore interventions that enhance both psychological and cognitive readiness in competitive sports. As previously discussed, research has demonstrated the effectiveness of BFB interventions, particularly HRV-BFB, in managing anxiety and enhancing cognitive function. However, many of these studies have focused on individual adults or athletes, involved short-term interventions, or examined only a single physiological parameter, which limits the generalizability of their findings to team sports contexts. Moreover, inconsistencies exist regarding the extent to which BFB interventions translate into measurable improvements in cognitive performance, highlighting a need for more comprehensive approaches.

Multimodal BFB interventions, targeting multiple physiological parameters such as GSR and PT, may provide a more complete assessment of autonomic regulation and its influence on cognitive outcomes, but research in this area remains scarce, particularly in team sports where sustained attention and mental flexibility are critical for performance. More specifically, GSR reflects autonomic arousal and emotional regulation [29], both of which are critical for maintaining focus and managing anxiety during competition. PT provides an index of peripheral temperature changes associated with stress responses and recovery [30]. By simultaneously monitoring and training these physiological parameters, multimodal BFB may enhance athletes’ capacity to regulate both physiological and psychological states, thereby supporting sustained attention, mental flexibility, and overall performance in team sports.

To address these research gaps, the present study investigated the effects of a 5-week multimodal BFB intervention on sustained attention in competitive female volleyball players. We hypothesized that, after 15 sessions of BFB intervention, athletes would show positive changes in physiological parameters, including decreased GSR and increased PT, and that these physiological improvements would contribute to enhanced cognitive performance.

Methods

Sample

Twelve competitive female volleyball players aged 17 to 20 years were invited to participate in this study. The participants were randomly assigned to either the BFB group (n = 6; M_age: 17.83 ± 0.75 years) or the control group (n = 6; M_age: 17.67 ± 0.52 years) who received no BFB intervention. All participants were recruited from the same team competing in national tournaments organized by the National Volleyball Federation and attended team training sessions at least six times per week (∼ 2 h each), indicating a highly trained athlete [31]. Due to the study’s pilot nature, we focused exclusively on female athletes to eliminate potential gender-related effects. The inclusion criteria for the study were: good general health, nonsmoking status, a history of regular menstrual cycles, no mental, neurological, or cardiovascular disorders, and active participation in national volleyball tournaments. The exclusion criteria were the use of illegal substances, oral contraceptives, antidepressants, alcohol, or drugs, current psychotherapy, and a history of BFB intervention. The baseline characteristics of the participants are presented in Table 1.

Table 1.

Baseline characteristics of the participants (n = 12)

Variables	BFB group (n = 6)	Control group (n = 6)
Age (years)	17.83 (0.75)	17.67 (0.52)
Sport experience (years)	6.33 (1.63)	7.17 (1.33)
Body height (m)	1.74 (5.91)	1.76 (4.33)
Body mass (kg)	64.76 (7.73)	67.21 (5.86)
Body mass index (kg/m2)	19.88 (2.88)	20.81 (2.14)

Data are presented as mean ± standard deviation. BFB = Biofeedback

All athletes were thoroughly briefed on the study procedures, including the BFB device, physiological measurements, session details, and attention test. They provided both verbal and written informed consent before participation. For those under 18 years of age, parental written consent was obtained. The study protocol was retrospectively registered at ClinicalTrials.gov (Registration No: NCT07061834) on 01/07/2025. Ethical approval was obtained from the Clinical Research Ethics Committee of Karamanoğlu Mehmetbey University prior to study initiation (Approval No: 02-2024/26; Date: 23/01/2024).

Study design and procedures

This randomized controlled trial employed a pretest-posttest design with two groups (BFB and control) and was conducted in accordance with CONSORT guidelines. Randomization was executed using an Excel spreadsheet (Microsoft Corp., Redmond, WA, USA) by a researcher not involved in data collection or intervention delivery to ensure allocation concealment, taking into account participants’ age and playing position to minimize group imbalances. All procedures were reviewed with the team’s coach and general director and explained to the athletes prior to the study.

Initially, the demographic data of the athletes were recorded. Baseline measures of GSR and PT were recorded using a BFB device during the pilot session. In this session, participants were not given any specific instructions or prompts regarding their behavior or physiological responses. This approach was intended to capture the natural, unaltered baseline levels of GSR and PT, thus providing a more accurate representation of the typical physiological state before any experimental interventions were applied. In addition, participants completed the d2 attention test to assess sustained attention [32]. Following a 1-week break, the BFB group participated in 15 individual BFB sessions over a 5-week period. These sessions were conducted by the study’s first author (MM), who has prior experience with BFB interventions in several projects, under the supervision of both a psychologist and a certified BFB instructor with specialized training in the procedure. In contrast, the control group received no intervention and continued their routine team training sessions. Athletes in the BFB group were instructed not to disclose any details about the intervention to the control group. After the 5-week intervention, post-intervention measurements for GSR, PT, and the d2 attention test were collected (Fig. 1). The study was conducted during a 5-week in-season break at the athletes’ training facilities by the researchers, who were not involved in athlete recruitment or randomization.

Fig. 1.

Schematic representation of the study design

Biofeedback intervention

We followed the intervention procedure outlined by Makaracı et al. [27]. In the BFB group, participants engaged in diaphragmatic breathing exercises involving positioning (sitting in a comfortable chair), hand placement on the chest, deep inhalation, slow exhalation, and maintaining a slow and steady breathing rhythm. The exercises were performed twice daily for 20 min over the course of one week, following the baseline measurements. This approach was designed to enhance participants’ ability to acquire and apply self-regulation techniques, improve the natural movement of the diaphragm, and increase the effectiveness of BFB sessions. Additionally, they received brief instructions in positive imagery and autogenic practices to help maintain motivation and focus, with the aim of fostering positive effects on their mental well-being. Subsequently, the BFB group attended 15 individual BFB sessions over 5 weeks. These sessions utilized a non-invasive BFB device (NeXus-10 MKII, Netherlands) and accompanying software (BioTrace + Software for NeXus-10, Mind Media B.V., Version V2018A, Netherlands) to enable participants to learn to control their physiological responses (i.e., GSR and PT) via BFB information displayed on a laptop (HP Pavilion 15-AB210NT). During each BFB session, participants were comfortably seated in an armchair that was free from materials that could interfere with proper breathing. They were instructed to focus intently on the computer screen to follow the BFB context. Sessions were conducted three times per week, each lasting 12 min and divided into three phases: familiarization, main, and feedback.

During the three-minute familiarization phase, the athletes were encouraged to explore the functionality of the equipment, including the various sensors and controls. They also had the opportunity to interact with the BFB software interface, which displays real-time data and feedback on their physiological responses. Athletes were encouraged to direct any questions regarding the BFB screen, its features, and the interpretation of the displayed information to the first author of the study (MM). The main phase of the intervention featured various real-time feedback tools, including music, photos, video games, and calming nature scenes, presented in a randomized order using the BioTrace + software developed by MindMedia [8]. During this six-minute phase, athletes employed techniques such as deep diaphragmatic breathing, positive imagery, and personal autogenic phrases to enhance relaxation and regulate physiological responses [33]. The session ended with a three-minute feedback phase designed to provide athletes with insights into the positive outcomes of the intervention. In this phase, the athletes received personalized feedback on their performance, including data on the physiological improvements observed throughout the session. The feedback emphasized key metrics, such as changes in GSR and PT, which provided the athletes with a clear view of their progress and illustrated the effectiveness of the techniques used.

To control autonomic cardiovascular responses, athletes were instructed to avoid physical activity before each session and abstain from food or drinks for two hours prior [16]. Team training sessions were scheduled in the evening to accommodate these requirements. BFB sessions were held in a quiet, isolated room within the volleyball team’s facilities between 1 and 3 p.m.

Physiological measures

We assessed physiological parameters by collecting real-time GSR and PT data to determine whether participants effectively learned to regulate these autonomic parameters. Post-intervention data were collected in a manner similar to baseline assessment, without any instructions or guidance, on a separate day after the final session. The data were recorded during the main phase of each BFB session.

GSR, a measure of skin conductivity, was recorded using a GSR sensor placed on the non-dominant hand’s bent fingers with Velcro strips and was measured in microsiemens (µS). Participants were instructed to concentrate on the computer screen to reduce real-time GSR data during a relaxed state, as GSR typically increases with stress [34]. The peripheral PT was monitored with a temperature sensor taped to the third finger of the dominant hand, which could detect temperature changes as small as 1/1000th of a degree within a range of 10–40 °C. Participants were instructed to maintain a peripheral hand temperature of at least 30 °C while observing real-time feedback on the monitor. The room temperature during sessions was maintained at 22 °C using a climate-controlled environment and continuously monitored with a digital thermometer to minimize external influences on PT readings. While controlling room temperature helps standardize PT measurements, it may also indirectly influence GSR outcomes, as skin conductance can be sensitive to ambient temperature; however, the stable environment across all sessions likely minimized such variability.

All sensors and equipment transmit data to a personal laptop via Bluetooth. The BFB device software automatically saves session-specific data after each session, with a sampling frequency of 2048 Hz for each sensor. After each session, the BFB software provided graphical feedback and detailed quantitative data on all physiological parameters [22, 27].

Sustained attention (d2-test)

We used the d2 test to evaluate participants’ sustained attention both before and after the BFB intervention [32]. This test is particularly well-suited to the dynamic nature of team volleyball, where players must maintain focus and adapt to rapidly changing game conditions. It is specifically designed to assess attention and concentration through a challenging and time-sensitive task. The d2-test is a paper-and-pencil task comprising 14 lines, each containing 47 symbols (letters) on a single sheet. Each symbol is either a letter “p” or “d,” with one or two lines either above or below the letter. Participants must accurately identify and mark only the ‘d2’ symbols, ignoring all others, and must do so from left to right across each line. The test is timed, with participants given 20 s to complete each line before moving on to the next. The entire test duration is four minutes and 40 s. Participants were instructed to work as quickly and accurately as possible, marking each d2 symbol correctly. To control for environmental and circadian influences, the pre- and post-tests were conducted in the same room at the athletes’ facilities and at the same time of day (2 p.m.) during the second training day of the regular week, which typically involves a relatively low training load, within a 5-week in-season break.

We computed five parameters from the d2-test results: TN (total number of symbols processed): indicates processing speed, with higher values reflecting better performance; E (marking error): measures the number of incorrect marks, with fewer errors signifying better sustained attention; E% (percentage of marking errors): represents the proportion of errors made, where a lower percentage indicates better attention; TN-E (total symbols processed minus errors): reflects the number of correctly processed symbols, with higher values indicating fewer errors; CP (concentration performance): assesses sustained attention by calculating the difference between the number of correctly marked “d2” symbols and incorrectly marked symbols. Higher values represent better sustained at-tention. The d2 test demonstrated exceptionally high internal test-retest reliability across all parameters, with values ranging from 0.95 to 0.98 [32].

Statistical analyses

Statistical analyses were conducted using SPSS software (version 21; SPSS Inc., Chicago, IL, USA). Descriptive statistics are reported as means and standard deviations. Missing data were minimal and handled using a complete-case approach. To analyze data distribution, the Shapiro-Wilk test was employed, while Levene’s test was used to assess the equality of error variances. Group differences in post-intervention outcomes were examined using one-way analysis of covariance (ANCOVA), with group as the between-subjects factor and baseline measurements as covariates. The assumptions of ANCOVA, including linearity between covariates and dependent variables and homogeneity of regression slopes, were checked and met. Within-group differences between pre- and post-intervention measures were assessed using paired sample t-tests. Effect sizes were interpreted using the following thresholds: small (0.00 ≤ d ≤ 0.49), medium (0.50 ≤ d ≤ 0.79), and large (d ≥ 0.80) [35]. Statistical significance was set at a p-value of < 0.05.

Results

Physiological findings

ANCOVA analyses revealed a significant group difference, as reflected by a higher post-intervention PT in the BFB group (F_(1,9) = 18.50; p = 0.002), which explained 67% of the variance between the groups (η² = 0.67). The ANCOVA for the GSR did not show a significant difference after the intervention (p > 0.05). The BFB group showed significant improvement in GSR and PT after the intervention (d = 1.02, p = 0.030 and d = 2.14, p = 0.005 respectively), whereas the control group did not show any significant changes after the intervention (p > 0.05) (Table 2).

Table 2.

Paired sample t-test and ANCOVA findings related to GSR and PT after a 15-session of multimodal BFB intervention

Variables	Group	Pre-Intervention*	Post-Intervention*	t	p a	Effect Size	p b	η2
GSR (uS)	BFB	6.73 ± 2.68	4.50 ± 1.51	2.995	0.030†	1.02	0.481	0.070
	Control	4.65 ± 0.95	4.19 ± 0.72	1.016	0.356	0.54
PT (°C)	BFB	33.92 ± 1.18	35.86 ± 0.16	-4.369	0.005†	2.14	0.020†	0.673
	Control	33.00 ± 2.51	34.64 ± 1.12	-2.210	0.069	0.32

Notes. *Data are presented as mean ± standard deviation. ^aValues were obtained from paired-sample t-test; ^bValues were obtained from ANCOVA test with baseline values as a covariate. GSR = galvanic skin response; µS = microsiemens; PT = peripheral temperature; °C = celsius; BFB = Biofeedback. †Denotes statistical significance at an alpha level 0.05

Sustained attention (d2-test) findings

ANCOVA analyses revealed a significant group difference, as reflected by a higher post-intervention E% in the BFB group (F_(1,9) = 4.78; p = 0.045), which explained 35% of the variance between the groups (η² = 0.35). The ANCOVA for the other d2-test variables (i.e., TN, E, TN-E, and CP) did not demonstrate a group difference after the intervention (p > 0.05). The BFB group showed significant improvement in all d2-test variables after the intervention (d = 0.18 to 1.01, p < 0.05), while the control group did not show any significant changes after the intervention (p > 0.05) (Table 3).

Table 3.

Paired sample t-test and ANCOVA findings related to d2 attention test variables after a 15-session of multimodal BFB intervention

Variables	Group	Pre-Intervention*	Post-Intervention*	t	p a	Effect Size	p b	η2
TN (score)	BFB	546.83 ± 69.69	609.00 ± 52.08	-3.420	0.019†	1.01	0.111	0.258
	Control	533.50 ± 60.40	544.66 ± 77.19	-0.405	0.702	0.16
E (score)	BFB	33.66 ± 34.97	27.33 ± 32.43	4.939	0.004†	0.18	0.232	0.155
	Control	63.33 ± 42.48	59.66 ± 32.73	0.491	0.644	0.08
E (%)	BFB	7.02 ± 6.59	4.60 ± 5.27	3.678	0.014†	0.40	0.045†	0.346
	Control	11.44 ± 7.30	10.94 ± 5.82	0.327	0.757	0.07
TN-E (score)	BFB	508.83 ± 77.05	582.00 ± 67.23	-5.045	0.004†	1.01	0.215	0.165
	Control	470.17 ± 45.40	497.16 ± 92.24	-0.729	0.499	0.37
CP (score)	BFB	217.67 ± 47.82	250.33 ± 47.86	-2.836	0.036†	0.68	0.095	0.278
	Control	172.16 ± 37.19	177.66 ± 37.67	-0.317	0.764	0.15

Notes. ^*Data are presented as mean ± standard deviation. ^aValues were obtained from paired-sample t-test; ^bValues were obtained from ANCOVA test with baseline values as a covariate. CP = Concentration performance; E = Errors; E% = The percentage of made errors; TN = Total number of symbols processed; TN-E = Total number of symbols processed minus the total number of errors; BFB = Biofeedback. †Denotes statistical significance at an alpha level 0.05

Discussion

This pilot study investigated the effects of a 5-week multimodal BFB intervention on sustained attention among female volleyball players. Consistent with the study hypotheses, the 15 sessions of the BFB intervention significantly improved the physiological metrics (i.e., GSR and PT). Consequently, sustained attention was enhanced in these participants following the intervention.

In this study, we evaluated the autonomic effects of a 5-week BFB intervention by measuring two physiological variables (i.e., GSR and PT). After 15 BFB sessions, improvements in these autonomic parameters were observed in the experimental group (see Table 2). These findings suggest that BFB positively affects the autonomic regulation of competitive female athletes. Acute stress is known to negatively affect athletic performance, often leading to decreased peripheral skin temperature [36, 37]. To date, only one study has specifically investigated the impact of BFB on PT in athletes, demonstrating its efficacy in increasing PT [27]. Previous research on relaxation and mental health interventions also indicates that such approaches can improve PT across various populations [38]. These results align with evidence that skin temperature–based BFB can be an effective tool for stress management, as it enhances control over vasoconstriction and supports self-regulation of the sympathetic nervous system (Levy & Baldwin, 2019).

Additionally, GSR, a well-established indicator of sympathetic activity and stress [39], did not show significant between-group difference after the intervention. However, within the BFB group, notable changes were observed, suggesting a potential stress-reducing effect of BFB. The absence of a significant between-group difference may be attributed to the relatively small sample size and the short duration of the intervention, which may have limited the statistical power to detect group differences. Furthermore, individual variability in stress reactivity could have masked potential between-group difference. Nevertheless, the within-group changes suggest that multimodal BFB may still provide benefits for stress reduction. Overall, our findings imply that a multimodal BFB approach can be particularly effective for athletes in managing competition-related stress and enhancing performance. By optimizing electrodermal activity and PT, athletes can improve autonomic regulation, which is essential for maintaining composure under pressure and optimizing physiological responses. Moreover, consistent BFB practice may help reinforce neural pathways and foster a more adaptive stress response system, potentially contributing to long-term gains in health and resilience [27]. Such improvements in physiological self-regulation could ultimately translate into better performance outcomes, particularly in dynamic and unpredictable sports such as volleyball. Despite its methodological rigor and evidence supporting its effectiveness in enhancing physiological self-regulation through objective, customizable, and versatile techniques [39], the current literature on BFB in athletes remains limited. Reported findings are sometimes inconsistent, likely due to heterogeneity in participant characteristics (e.g., sport type, competitive level, age), intervention protocols (e.g., BFB modality, session duration, total number of sessions), and outcome measures. For instance, one study in basketball players applied 10 days of HRV-BFB training with resonant-frequency breathing [40], whereas a tennis trial implemented 10 multimodal sessions over four weeks [27]. Similarly, a pilot study with soccer and track athletes combined mental coaching with daily HRV or EEG neurofeedback, revealing distinct neural and stress-related adaptations [41]. Taken together, these discrepancies highlight the need for more systematic investigations that directly compare BFB modalities and protocols across different sports. Such research would provide clearer insights into the mechanisms underlying BFB’s effects and help establish evidence-based guidelines for integrating BFB, alongside traditional therapies and pharmacological approaches, into athletic training and performance optimization.

Although research exploring the correlation between improved autonomic control after BFB intervention and cognitive function in athletes is limited and requires further investigation, existing studies suggest that BFB can effectively enhance cognitive performance in non-athletes [42, 43]. In competitive sports, athletes constantly interact with external factors, such as teammates, opponents, referees, coaches, and the ball, which are critical for maintaining performance [44]. In team sports like volleyball, athletes must exhibit high levels of cognitive functioning, including decision-making, executive function, and attention [45]. In our study, the experimental group exhibited improvements in sustained attention, as evidenced by all variables of the d2 test, following the BFB intervention (see Table 3). These improvements are likely to translate into more effective performance, superior decision-making, and overall improved gameplay in real-world scenarios. However, ongoing monitoring and continuous application of these techniques will be crucial for sustaining and further amplifying these benefits over time. The overall enhancement in sustained attention is consistent with the regulation of autonomic metrics. Similar findings were reported by Makaracı et al. [27], who observed that 10 sessions of multimodal BFB improved physiological (i.e., HRV, sEMG, GSR, PT), psychological (e.g., competitive anxiety), and cognitive functions (e.g., attention and inhibition) in international tennis players. Additionally, Neuroplus, an integrated autonomic BFB intervention, effectively enhanced cognitive function and modified stress biomarkers (i.e., GSR, heart rate, respiration rate) in elite soccer players [46]. Given that chronic psychological stress can impair overall cognitive function [47], BFB may serve as a valuable intervention for improving cognitive performance in competitive athletes, particularly during intensive training and match schedules. Moreover, optimizing the interplay between autonomic and cognitive functions through BFB may be crucial for enhancing athletes’ well-being in sports. On the other hand, while our study primarily assessed sustained attention, it is important to acknowledge that other cognitive domains such as executive function, working memory, and inhibitory control are also highly relevant for athletic performance [48]. For example, enhancements in executive function could facilitate more flexible decision-making in rapidly changing game situations, whereas improvements in working memory may aid athletes in processing multiple streams of information simultaneously, such as tracking teammates, opponents, and ball dynamics [49]. Future research incorporating a broader range of cognitive assessments, including tasks such as the Stroop test, Mackworth Clock Test, or Timewall Test, could provide a more comprehensive understanding of the cognitive and psychophysiological benefits of BFB in competitive sport contexts.

From a practical perspective, these findings highlight several potential applications of BFB in sports. Enhancing sustained attention may help athletes process game-relevant cues more efficiently, anticipate opponents’ actions, and execute faster, more accurate decisions under pressure. Improved autonomic regulation can also support stress and arousal management during competitions, reducing the risk of mental fatigue or performance breakdown in critical moments. Although our study was conducted in a controlled environment, previous research and anecdotal athlete feedback suggest that BFB skills may transfer to real-life competitive conditions, even under fatigue or heightened stress, helping athletes maintain focus and composure during demanding match situations [50]. In team contexts such as volleyball, greater attentional control can foster better communication and coordination with teammates. Therefore, incorporating BFB into regular training or pre-competition routines may provide athletes with a practical tool to optimize both performance and psychological well-being across demanding match schedules.

Limitations

Despite its promising findings, this pilot study has several limitations that must be considered. One primary limitation of our study is the inability to conduct a proper a priori power analysis to estimate the required sample size, which arises from the fact that this is the first attempt at studying competitive female volleyball players. Consequently, the relatively small sample size may have affected the generalizability of our findings. The absence of an active control group undergoing similar or combined interventions limits the ability of the study to establish a comparative benchmark. Additionally, we focused exclusively on female athletes to control for potential gender-related differences; however, the autonomic and cognitive responses to BFB training may differ in male athletes, which limits the applicability of our findings across genders [51]. Furthermore, this study did not account for individual temperament or personality traits, which may influence autonomic and cognitive responses, as characteristics such as the ability to remain calm under pressure or motivational tendencies could affect responses to BFB intervention. Another limitation was the difficulty in fully eliminating the potential effects of the menstrual cycle during the 5-week intervention, despite our inclusion criteria specifying a history of regular menstrual cycles. Finally, we were unable to include a volleyball skill test to assess whether the autonomic effects of the BFB intervention aligned with sports-specific performance parameters due to the participants’ demanding training schedules.

Conclusion

Our pilot study demonstrated that 15 sessions of BFB intervention significantly improved GSR and PT, reflecting positive changes in autonomic control, and sustained attention among female volleyball players. These findings provide emerging evidence that BFB can serve as a promising and noninvasive method for enhancing both autonomic regulation and cognitive performance in competitive athletes within a relatively short timeframe. Beyond its preliminary nature, the results highlight the potential of BFB to be integrated into athletic training and performance optimization programs. Importantly, investigating the durability and long-term effects of BFB interventions through follow-up assessments is essential to determine whether these autonomic and cognitive benefits are maintained over time and to guide the design of sustained training protocols. Nevertheless, future studies with larger and more diverse athletic populations are required to confirm these effects, explore long-term outcomes, and compare BFB with other psychological and physiological interventions. Collectively, this line of research will help establish the role of BFB as an evidence-based tool for supporting both performance and well-being in sport.

Biographies

Melek Makaracı

is an Assistant Professor at Karamanoglu Mehmetbey University, where she conducts research in sports sciences and physical education. She holds a B.A. in Physical Education and Sports Teaching (2014) from Mugla Sıtkı Koçman University, an M.Sc. in Physical Education and Sports Sciences (2017) from Akdeniz University and a Ph.D. in Physical Education and Sports (2022) from Gazi University.

Yücel Makaracı

is an Associate Professor at Karamanoglu Mehmetbey University, specializing in movement and training sciences. He holds a B.A. in Coaching Education (2010), M.Sc. in Physical Education and Sports (2014), and Ph.D. in Physical Education and Sports (2019), all from Ondokuz Mayıs University.

Author contributions

Research concept and study design: MM, YM; Literature review: MM, YM; Data collection: MM; Data analysis and interpretation: MM, YM; Statistical analyses: YM; Writing of the manuscript: YM; Reviewing/editing a draft of the manuscript: MM. All authors read and approved the final manuscript.

Funding

This study was not financially supported.

Data availability

The data analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethical approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Institutional Review Board of Karamanoğlu University Clinical Research Ethics Committee (Approval No 02-2024/26; Date: 23/01/2024).

Informed consent

Informed consent was obtained from all individual participants included in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.