Transcranial Direct Current Stimulation and Core Stabilization Enhance Shooting Performance and Balance in Athletes: A Randomized Controlled Trial

Introduction

As an official Olympic sport, 10-m air rifle shooting involves a shooter in a standing position, who shoots at a target at a 10-m distance with a 4.5-mm caliber air rifle [1]. Shooting is a sport requiring precision and timing to achieve high scores. It requires psychological stability, high-level concentration, physical balance, muzzle stability, and outstanding athletic performance [2,3]. Shooting is also a representative static sport where the shooter is required to maintain high-level physical stability against gravity, as postural sway can reduce muzzle control and have a potentially negative effect on shooting performance [4,5]. To ensure outstanding athletic performance, the shooter must fix the muzzle at the center of the target area to fire accurately, and the shooter’s physical balance is a critical factor required to achieve this [6].

Balance is the process of maintaining the vertical center of mass on the base of support. Balance ability is a fundamental requirement of high athletic performance in sports activities. For shooting, the shooter’s physical stability is critical in aiming the rifle at the target area, during which time the brain must control multiple degrees of freedom throughout the body, as stable posture and accurate positioning of the arm are important to maintain balance [6].

An effective balance training program should maximize exercise efficiency, while avoiding monotony, by providing suitable muscle training and reducing physical instability. Balance training programs are also essential in improving athletic performance and preventing injuries [7,8].

A change in trunk imbalance with continuous external force applied to the spine leads to a structural problem, which is known to occur more frequently in athletes in unilateral sports than in bilateral sports [9,10]. Shooting characteristically demands excessive use of the dominant side of the body, and continuous overloading, strenuous efforts, and repeated training in the subconscious state can further increase muscle asymmetry in athletes, which induces an abnormal change in the spine [11]. Such asymmetries in posture and trunk imbalance can lead to compensatory movement patterns, reduced neuromuscular efficiency, and diminished proprioceptive control, all of which can impair physical balance and motor coordination. In shooting sports, these deficits have been directly linked to decreased performance. Mononen et al (2007) found significant negative correlations between postural sway and shooting accuracy (r=−0.29 to −0.45) [3], and experts tend to display superior postural control relative to novices across a range of sports [12]. These findings underscore the importance of stable posture for precision-based athletic performance. Shooting athletes can have an imbalance of the musculoskeletal system owing to long-term unilateral postures; moreover, continuous training and competitions in such states can lead to pain and injuries [13].

With the recent advancement of science and technology, methods to help athletes improve their performance have been developed using various assistive training devices. Transcranial direct current stimulation (tDCS) is one such method. tDCS modulates cortical excitability by delivering a low-intensity direct current to the scalp, which influences the resting membrane potential of neurons. Anodal stimulation tends to depolarize neuronal membranes, increasing cortical excitability, while cathodal stimulation hyperpolarizes them, decreasing excitability. These effects can facilitate synaptic plasticity and motor learning by enhancing neural firing and connectivity in targeted brain regions [14]. The weak direct current (1.5 mA) used in tDCS can induce changes in brain excitability that persists long after the current has ceased [15,16]. The tDCS-based brain stimulation for the primary motor area can improve training effects and athletic performance [17].

Studies on the motor, cognitive, and functional aspects of brain domains have been conducted in different fields [17]. Various individuals have been investigated, including athletes, regarding ways to enhance athletic performance [18,19], and the general population, and patients with stroke or Parkinson disease have also been investigated regarding ways to increase single-joint mobility [20–22]. Most previous studies applied tDCS in general or clinical populations, and rarely in precision-based sports such as shooting. While tDCS alone can enhance cortical excitability, combining it with functional interventions such as core stabilization training may yield synergistic benefits, especially in sports requiring static posture and fine motor control. However, no studies to date have examined this combined approach in shooting athletes. Thus, this study aimed to determine the effects of tDCS combined with core stabilization training on balance, postural alignment, and shooting scores in university-level shooting athletes.

Material and Methods

PARTICIPANTS:

Twenty shooting athletes participated in this study (Table 1). Participants were recruited from a bulletin at K University’s Shooting Department. The participants’ inclusion criteria were as follows: 1) a currently active shooting athlete who participated in at least 1 national competition at high school and university levels; 2) no history of respiratory and cardiovascular disease; 3) no musculoskeletal disease or recent injury in the past 6 months; 4) no neuromuscular disease or recent injury within the past 6 months; 5) did not perform personal resistance exercise outside the independent training given by the Shooting Department.

Sample size was estimated using G*Power 3.1, based on a previous randomized controlled trial by Madokoro et al, which reported a large effect size (f=0.40) for core stabilization training. With α=0.05 and power=0.80, a minimum of 20 participants was required [23]. A total of 21 individuals volunteered; however, after excluding 1 volunteer who had a shoulder injury, 20 participants were involved in this study. Table 1 presents the general characteristics of the athletes.

Written informed consent was obtained from each athlete prior to the study, and the participants’ rights were protected under the ethical principles of the Helsinki Declaration. The study was conducted with the approval of the Institutional Review Board of K University (1040460-A-2020-023). The trial was registered under trial registration no. PRE20210723-002.

PROCEDURES:

This study was a randomized controlled experiment. Among the subjects who met the selection criteria, 20 shooters were randomly assigned to the experimental group (n=10) and the control group (n=10) using envelopes. Randomization was conducted using a sealed-envelope method. A computer-generated randomization sequence was created by an independent researcher not involved in participant recruitment or assessment. The group assignments were placed into opaque, sequentially numbered, and sealed envelopes. These envelopes were stored in a locked cabinet and were opened in order by the research coordinator only after participant enrollment, ensuring allocation concealment. This procedure was implemented to minimize selection bias.

The experimental group received tDCS for 20 minutes, and the control group received sham tDCS for 20 minutes. The sham tDCS was applied identically to active stimulation except that no actual electrical current was delivered. Blinding of the intervention providers was not possible due to the practical constraints of the training procedures. While participant blinding was maintained using sham stimulation, outcome evaluators were aware of group allocation. This limitation is acknowledged and considered in the interpretation of results.

Both groups received 40 minutes of trunk stabilization training, including bridge, bird-dog, side-bridge, dead-bug exercises, BOSU 1-leg stance, and BOSU squat exercises. Additionally, they completed 30 minutes of general strengthening exercises, including press-up, dumbbell exercises, and running. All interventions were performed 3 times a week for 5 weeks. Trunk imbalance, balance ability, and shooting scores were measured before and after the intervention (Figure 1).

TRANSCRANIAL DIRECT CURRENT ELECTRICAL STIMULATION:

tDCS devices are known to improve training effects and enhance exercise performance through noninvasive brain stimulation [17]. We used the Halo Sports tDCS device, a commercial transcranial direct current device manufactured by Halo Neuroscience (USA). Halo Sports is designed as a standalone headset similar in shape to audio headphones. Before use, 3 stud foam electrodes called primers (24 cm2) are wetted inside the headphones to make electrical contact with the head. The headphones are positioned so that the primers are in the primary motor area above the top of the head, and the round parts on both sides of the headphones are placed on both ears. The electrodes are connected to a continuous current electrical stimulator powered by a lithium-ion (LiPo) cell (36V). The maximum energy output is 2.2 mA, and the Halo Sports is controlled by installing an application on the machine that the smartphone user has. The experimental group was seated comfortably on a chair in a resting state, and the Halo Sports primer was separated, soaked in water, and the headphones were placed properly on the head. The current intensity was set to an intensity that the subject felt comfortable with for 30 seconds. The control group was stimulated in the same way as the experimental group, but the actual stimulation was not performed. Both the experimental and control groups were stimulated for 20 minutes (Gandiga et al, 2006) (Figure 2).

TRUNK STABILIZATION EXERCISES:

The trunk stabilization program, based on McGill and Karpowicz (2009), included the following 6 exercises [24]:

The entire trunk training lasted 40 minutes including 5-minute warm-up and 5-minute cool-down.

The trunk stabilization exercise was conducted for a total of 40 minutes, including 5 minutes of warm-up exercise, 30 minutes of main exercise, and 5 minutes of cool-down exercise, and was conducted 3 times a week for a total of 5 weeks (Figure 3).

GENERAL STRENGTHENING PROGRAM:

The general strengthening program consisted of:

These exercises were performed in circuit fashion, lasting a total of 30 minutes.

SPINAL STRUCTURE ANALYSIS SYSTEM:

To analyze the alignment indices of the spine and pelvis, the 3D spine structure analysis system (Formetric, Diers, Germany) developed by the Bioengineering Institute of the Medical University of Münster, Germany was used to measure the inclination of the spine and the changes in the structure and shape of the thoracic and lumbar vertebrae. The spine structure analysis system enables rapid measurement, captures virtual lines on the camera using a halogen lamp, automatically finds major parts of the human body, and numerically displays values related to the virtual 3D spine and pelvic model. Unlike previous examination methods, there is no radiation exposure, and has proven inter-measuring error and test-retest reliability [25,26].

To allow the measurement, subjects remove their shirts, slightly lower the waistband of the pants to expose the tailbone, place the heels on the marked area on the floor, and stand with the back facing the lens of the machine.

The distance between the subject and the measuring equipment was 2 m, the measurement area was darkened, and other accessories that could affect the test due to light reflection were removed. The subject’s gaze was bent at an angle of about 15°, and the arms were comfortably lowered to measure the subject. Through this system, trunk imbalance, pelvic tilt, kyphotic angle, lordotic angle, and lateral deviation were measured.

The Formetric 4D system used in this study has demonstrated high reliability in previous studies. According to Frerich et al (2012), intra-rater ICC values for key spinal alignment parameters such as trunk imbalance, pelvic tilt, and kyphotic angle ranged from 0.88 to 0.98, and inter-rater ICC values ranged from 0.84 to 0.95, indicating excellent reliability [25].

BALANCE ABILITY:

We used the Goodbalance postural balance analysis system (Metitur, Finland) to measure the balance ability of the participants. It measures balance by calculating the movement trajectory of the center of pressure by sensors located at each corner of a triangular platform [27]. Before measurement, the subjects were informed about the measurement process and practiced on the ground to become familiar with the movements. For static balance, the test was conducted with the subjects standing on the platform with their feet aligned on the center line, and their arms were placed in an X shape on their chest while looking at a fixed point 3 m ahead. The measurement method took about 10 seconds, and the average speed and area of the COP in the X and Y axes were measured. For the dynamic balance test, the subjects crossed their arms over their chest and stood with their feet positioned in a diagonal stance forming an “X” shape on the platform. The subjects looked at a predefined route model on the computer screen and solved the task by using body movements to contact the target point of the route model on the screen. The average speed and distance in the X and Y axes of the COP were measured in each posture, and the inter-examiner reliability of the Goodbalance system was high at ICC=0.69~0.93, and the intra-examiner reliability was very high at 0.85~0.98 [28].

SHOOTING SCORE:

With the cooperation of the university team staff and assistant researchers participating in the experiment, 60 shots were fired for 1 hour and 15 minutes at a distance of 10 m using the same method as during regular shooting practice. All shooting processes were conducted in accordance with international game rules, and the shooting scores were analyzed by comparing the average shooting score before the experiment with the average shooting score after the intervention using the average of 3 measurements. The highest possible score was 600 points.

STATISTICAL ANALYSIS:

SPSS version 21.0 (IBM Corporation, NY, USA) was used for statistical analysis. To test for normality, the Kolmogorov-Smirnov test was used. The chi-square (χ²) test was used to examine the association between sex and the dominant hand used in shooting. For the general characteristics and pre-test between-group homogeneity, an independent t test was used. The paired t test was performed to comparatively analyze the pre-test–post-test between-group differences, and an independent t test was used to compare the changes in dependent variables between the training (experimental) group and the control group. The significance level was set at α=.05 for all data.

Results

Table 1 presents the general characteristics of the participants. No significant differences were found between the experimental and control groups in terms of age, height, weight, athletic career, sex, or dominant hand (P>0.05), indicating that the 2 groups were homogeneous at baseline.

Table 2 presents the changes in balance ability for the experimental and control groups.

The experimental group showed statistically significant improvements in balance time (95% CI [1.18, 3.56], P<0.001, d=0.68), indicating a moderate-to-large effect, and sway distance (95% CI [15.14, 91.06], P<0.001, d=0.39), indicating a small-to-moderate effect.

The control group also demonstrated a significant improvement in balance time (95% CI [0.48, 1.90], P=0.005, d=0.48), indicating a moderate effect size. However, no significant change was observed in sway distance (95% CI [−29.32, 43.52], P=0.653, d=0.05), indicating a negligible effect. Between-group comparisons revealed significantly greater improvements in the experimental group for balance time (P=0.005) and sway distance (P=0.043), supporting the superior effectiveness of the tDCS-enhanced intervention.

Table 3 presents the changes in spinal alignment parameters. In the experimental group, trunk imbalance showed a significant improvement (95% CI [0.35, 1.25], P=0.004, d=0.46), reflecting a moderate effect. Lateral deviation also improved significantly (mean difference=0.90 mm, 95% CI [0.27, 1.53], P=0.011, d=0.37). However, pelvic tilt did not change significantly (95% CI [−0.19, 1.19], P=n.s., d=0.19). In the control group, trunk imbalance showed a small but significant improvement (95% CI [0.02, 1.38], P=0.045, d=0.36), while lateral deviation and pelvic tilt did not show significant changes (95% CI [−0.37, 1.77], P=0.174, d=0.29; pelvic tilt: 95% CI [−0.25, 0.65], P=n.s., d=0.11). However, between-group comparisons for trunk imbalance, lateral deviation, and pelvic tilt did not reveal statistically significant differences (P>0.05), suggesting that while within-group improvements occurred, the added benefit of tDCS on spinal alignment was limited.

Table 4 summarizes the changes in shooting scores. The experiment group demonstrated a statistically significant improvement in shooting performance (95% CI [1.06, 5.54], P=0.008, d=0.30), indicating a small-to-moderate effect. In contrast, the control group did not show a statistically significant change (95% CI [−0.01, 2.01], P=0.057, d=0.09), reflecting a negligible practical impact.

A significant between-group difference was observed in shooting score improvements (P=0.043), with the experimental group showing greater gains than the control group, supporting the role of tDCS in enhancing fine motor performance.

Discussion

This study was conducted to determine the effects of training while applying tDCS to the primary motor area on the balance, trunk imbalance, and shooting scores of shooting athletes. The results demonstrated that the experimental group, which received active tDCS combined with core stabilization training, showed significant improvements in dynamic balance (time and sway distance), trunk imbalance measures such as trunk imbalance and lateral deviation, and shooting performance compared to the control group. Notably, the effect sizes for balance time (d=0.68) and shooting score improvement (d=0.30) suggest that tDCS-enhanced training provides meaningful benefits in these performance domains, although improvements in trunk imbalance were more modest and did not significantly differ between groups.

Shooting athletes maintain a biased posture, overusing 1 side of the body during training and competitions [29], which can cause physical asymmetry or imbalance in shooters. Shooting as a representative static sport demands a high level of balance ability [4,5], while athletic performance is known to increase as balance improves [3,4].

The results of this study demonstrated significant differences in balance ability between the experimental and control groups. The increased excitability at the cortex as a result of tDCS was shown to induce a physiological state to acquire a new skill or improve learning ability [30]. These findings are consistent with prior studies on athletes. Kaminski et al (2016) observed that tDCS over the primary motor cortex improved dynamic balance performance in healthy adults, suggesting its relevance for postural control tasks [31]. Similarly, Vargas et al (2018) reported that anodal tDCS enhanced quadriceps strength in soccer players, indicating neuromuscular activation benefits in trained individuals [19]. Together, these studies support the potential of tDCS to enhance motor function in athletic settings, aligning with the balance and performance improvements observed in our shooting athletes [19]. In this study, tDCS applied to the primary motor area is likely to have affected the rate of learning core movement during training on an unstable base, which had a positive effect on the balance ability as the participant learned to control their body movements [32]. tDCS can modulate the excitability of cortical neurons by altering resting membrane potentials [33]. When applied over the primary motor cortex, anodal stimulation increases cortical excitability, which can enhance motor planning, coordination, and voluntary control of postural muscles [31]. This modulation can improve neuromuscular control and proprioceptive feedback, both of which are essential for maintaining balance. Furthermore, improved cortical drive to trunk and lower-limb muscles could contribute to better postural stability and alignment through more coordinated and symmetrical muscle activation patterns [34].

The current findings on the effectiveness of core stabilization training in improving balance and shooting performance are consistent with previous studies highlighting the benefits of trunk-focused neuromuscular interventions. For instance, Uzuner Kızılkaya and Tüzün [35] conducted a randomized controlled trial comparing core stabilization and proprioceptive neuromuscular facilitation (PNF) exercises in obese children. Their results showed that core stabilization produced greater improvements in muscle activation, endurance, and balance. Although the populations and performance tasks differ from those of the present study, these findings show that core stability training promotes functional improvements in postural control, supporting its application in sports requiring high-precision motor tasks such as shooting.

The postural alignment for the participants in this study was measured using the Formetric system, and the results indicated no significant difference between the experimental and control groups. In previous studies that applied tDCS, the maximum knee extensor muscle contraction in female soccer players was improved [19]. These results were attributed to the effect of tDCS applied to the primary motor area on the excitability of the cerebral cortex, which improved the ability to control voluntary muscles used in target sports, as well as muscle efficiency [36]. In contrast, the lack of significant between-group variation in trunk imbalance in this study may be due to the role of several factors, including core muscle activity, flexibility, neuronal control, and proprioception [37]. In addition, trunk imbalance is a structural attribute that may not respond rapidly to short-term interventions. While functional outcomes such as balance and shooting scores can be improved through neural adaptation and task-specific motor learning, meaningful changes in spinal posture often require longer durations and targeted postural retraining. The 5-week intervention period in this study may have been insufficient to produce measurable group-level changes, especially given the precision of the 3D Formetric system used for assessment. Furthermore, as both groups participated in identical core stabilization exercises, similar within-group improvements may have contributed to the lack of statistically significant between-group differences. These factors suggest that future studies should consider longer intervention periods or tailored postural correction programs to assess long-term structural outcomes more effectively.

Shooting scores varied significantly between the experimental and control groups. While shooting is a representative static sport, a delicate sway is induced by the force of the fingers upon firing, and the resulting fine movement at the nuzzle increases in range toward the target area depending on the distance, causing a large difference in score. At the moment of shooting, the balance between finger and shoulder movements is essential; furthermore, it is likely that the improved balance in the experimental group had an effect on the improved shooting scores [3,4].

The result may also be attributed to the direct effect of tDCS. In the study by Zhou et al (2014), tDCS was applied to the dorsal surface of the frontal lobe in the general population as they performed subtraction tasks with constant gait and posture, and the results showed a significant increase in efficiency [34]. In performing 2 tasks by shared cognitive resources, the brain’s level of performance is predicted to fall in 1 of the 2 tasks, and the bottleneck theory for operational control states that, when 2 tasks are processed by the same neural network, the network or processor delays the processing of 1 task until the other previous task is completed [38]. The effect of tDCS was thus accounted for based on the increased speed of processing and learning multiple tasks [39,40]. Shooting is a sport that requires multiple tasks to be performed simultaneously with the eyes focused on the target and the fingers moving toward firing, while body and shoulder movements are kept at a minimum [41]. In this study, tDCS was applied to the primary motor area; however, its effects could have been beyond the scope of electrode stimulation, as shown in previous research. This has been suggested to be due to the potential effects of tDCS on other areas through the network of connecting neurons with the strongest effect on the area of stimulation [42]. Furthermore, interpretation of the effect sizes offers additional insight into the magnitude of the observed changes. For dynamic balance time, the experimental group showed a Cohen’s d of 0.68, indicating a moderate-to-large effect, while sway distance yielded a d of 0.39, reflecting a small-to-moderate effect. For trunk imbalance, the effect sizes for trunk imbalance and lateral deviation were 0.46 and 0.37, respectively, both of which are considered moderate or small-to-moderate effects. The improvement in shooting performance yielded a d of 0.30, suggesting a small-to-moderate practical impact. Although not all outcomes reached statistical significance in between-group comparisons, the effect sizes suggest meaningful changes in motor control and performance associated with the tDCS-enhanced intervention.

In this study, the effects of tDCS applied to the primary motor area in shooting athletes are conjectured to have affected areas, such as the frontal lobe, through the neural network. This is presumed to have contributed to the significant improvements in shooting scores by facilitating rapid information processing and enhanced motor learning. These benefits likely stem from the effects tDCS on the neural network responsible for managing complex tasks such as eye fixation, body control, and fine finger movements during shooting. Overall, the results of this study confirm the positive effects of tDCS-based training on balance, trunk imbalance, and shooting performance in university-level shooting athletes. The results also suggest the utility of tDCS-based training as an effective program for shooting athletes.

tDCS is generally considered a safe and well-tolerated noninvasive neuromodulation technique when used within established safety guidelines. Prior studies have shown that stimulation intensities up to 2 mA for durations up to 20–30 minutes result in minimal adverse effects, which are typically limited to mild tingling, itching, or skin redness at the electrode site [15]. No serious neurological or systemic adverse effects have been reported in healthy populations under these conditions. In the present study, stimulation was administered according to these guidelines (2.0 mA for 20 minutes), and no adverse effects were observed among the participants. These findings support the safety and clinical feasibility of tDCS in athletic populations.

This study has several limitations that should be considered when interpreting the results. First, the sample size was relatively small (n=20), which may have limited the statistical power to detect smaller effect sizes and reduced the generalizability of the findings. Second, the intervention period was relatively short (5 weeks), and long-term follow-up assessments were not conducted, making it difficult to determine whether the observed improvements were sustained over time. Third, due to the nature of the intervention, blinding of the intervention providers was not feasible, and the outcome assessors were not blinded to group allocation. This lack of assessor blinding may have introduced a risk of measurement bias, potentially influencing outcome evaluations. Future studies should include larger sample sizes, extended intervention and follow-up periods, and consider testing different tDCS protocols (eg, stimulation intensity, duration, or target areas). Additionally, applying double-blinding procedures where feasible may enhance the validity and generalizability of the findings.

Conclusions

These findings provide practical guidance for coaches and trainers working with shooting athletes. The integration of tDCS with core stabilization training offers a promising, noninvasive approach to improve postural balance and motor control, which are key components of shooting performance. This combined intervention may be particularly useful during technical refinement phases or when athletes experience performance stagnation. Incorporating such neuromodulatory strategies into training regimens could support more efficient motor learning and enhance overall precision in competitive shooting.