The effect of warm-up with transcranial direct current stimulation on performance factors in collegiate golfers
Article information
Abstract
[Purpose]
This study aimed to determine the effects of warm-up using transcranial direct current stimulation (tDCS) on performance factors in collegiate golfers and to provide a scientific basis for the effectiveness and methodology of tDCS. We sought to compare the effects of tDCS as an additional treatment during warm-up. tDCS is generally activated when a small electric current is applied to the motor cortex of the cerebral cortex, which has been reported to be helpful in improving motor function. Therefore, we sought to prove the effectiveness of combined warm-up exercise and tDCS.
[Methods]
Twenty-two collegiate male golfers were divided into tDC- (tDCS; n=11) and sham-treated (sham; n=11) groups. To examine performance factors, the following were assessed following tDCS application: carry, clubhead speed (CHS), ball speed (BS) for driver performance, countermovement jump (CMJ) for lower extremity muscle power, global rating of change (GRC) for the subjective change in condition of the participants, and test of attentional interpersonal style (TAIS) for concentration.
[Results]
This study showed that warm-up with tDCS had positive effects on carry (p=.004), CHS (p=.019), BS (p=.017) of driver performance, CMJ (p=.002), and GRC (p=.005), however, no significant effect on TAIS was found, which suggest that the effects of the warm-up with tDCS were significant for driver performances, CMJ, and GRC.
[Conclusion]
Future studies should independently validate the effectiveness of tDCS and apply it to different situations and timeframes, such as training and competitions, to provide new alternative strategies or performance improvement.
INTRODUCTION
In golf, attention has been given to psychological factors such as course strategy, technique, and mental strength to allow golfers to perform optimally in various environments [1]. Additionally, the importance of physical fitness factors, such as injury prevention, performance maintenance, and enhancement, has emerged. Various studies have aimed to identify ways to improve athletic performance, with a growing interest in brain stimulation and neuromodulation linking neuroscience and athletic performance [2].
Transcranial direct current stimulation (tDCS), a method of brain stimulation, has been employed in various studies because it is easier to use than other brain stimulation devices and provides stimulation during relatively mild movements and exercises [3]. In addition, tDCS is noninvasive, uses a mild current that may cause a slight tickling or tingling sensation, has fewer side effects, and can modulate cortical excitability by adjusting the site and temporal intensity of stimulation [4,5]. Noninvasive electroencephalogram training can safely increase functional reversibility, and electrical stimulation increases excitability in the primary motor area (M1) of the cerebral insula, thereby strengthening the neurotransmission network of motor neurons [6]. Through tDCS, a mild current of 1–2 mA is delivered to the surface of the head through surface electrodes, with the advantage of high patient compliance and combinability with other forms of therapy [7]. Recent studies that use tDCS to improve sports performance have reported stimulation-induced improvements in golf-putting performance in 27 healthy subjects [8]. Stubbeman et al. [9] compared tennis serve performance among tennis players immediately after tDCS treatment and reported significant improvements in the performance 5 d later. Borduc-chi et al. [10] also reported slow increases in athletic performance, mood, and heart rate (HR), suggesting that tDCS has a positive effect on athletic performance. However, Flood et al. [11] reported that the application of tDCS, which stimulates the sensorimotor cortex, reduced pain perception but had no significant effect on muscle endurance or maximum force production. Therefore, reports on the effectiveness of tDCS are conflicting, and further validation is required to determine whether tDCS has a tangible effect. Furthermore, studies have been conducted on diseases such as encephalopathy [12], Parkinson’s disease [13], and depression [14], and further research is required to determine its effectiveness in improving athletic function.
Athletes enhance their performance by regularly engaging in a variety of training activities, such as warm-up, cool-down, physical training, and technical training. Participation in different types of training requires considerable effort and time, and the importance of efficiency is emphasized. tDCS can enhance the effectiveness of exercise by stimulating the brain, and its impact varies depending on the intensity and duration [15]. Therefore, it is commonly used in combination with training to improve exercise performance [16,17]. In this study, we aimed to verify its effectiveness in athletes by integrating it into their main exercise routine or warm-up exercises before competitions.
Previous studies comparing the effects of different types of warm-ups have shown that dynamic warm-ups can improve muscle function by preserving muscle-tendon unit stiffness compared with warm-ups that include static stretching [18,19]. Therefore, this study aimed to investigate the effects of a combined tDCS warm-up on performance factors in golfers and to provide scientific evidence for the application and effectiveness of tDCS in golfers. Previous studies have suggested positive effects of warm-up with tDCS. Therefore, the combined application of warm-ups and tDCS will be effective in improving golfers’ performance.
METHODS
Study subjects
The participants were 22 collegiate golfers registered with the Korean Collegiate Golf Federation. Using the G*power 3.1 program, when the effect size was set to .40, the power was set to .80, and the significance level was set to .05. There were 16 people, but considering potential drop out, 22 were recruited. All the participants were informed of the purpose and process of the study and voluntarily agreed to participate. Written consent was obtained from the participants, and the exclusion criteria were as follows: a history of epilepsy that may increase the risk of stimulation, unstable medical conditions, metal implants at the attachment site of the electrodes, and medications related to psychiatric disorders. This study was reviewed and approved by the Institutional Review Board of the Korea National Sport University (1263-202212-HR-088-02:20221209-106). The physical characteristics of the participants are presented in Table 1.
Physical characteristics of study subjects.
Procedure.
GRC scale (Global Rating of Change scales)
CMJ (Counter Movement Jump)
TAIS (Test of Attentional and Interpersonal Style)
Measurement variables and methods
Research procedure
Twenty-two golfers were randomly assigned to two groups of 11 each: one group performed a warm-up with tDCS application and the other performed a warm-up with sham application. Golf performance factors were measured immediately after the warm-up exercise, and the measurement was conducted such that it did not place a burden on the physical condition.
The body composition of each participant was measured using a body composition analyzer (Inbody 770; Inbody Co., Seoul, Korea) to determine their physical characteristics. The participants were then randomized into two groups of 11 each to measure golf performance: the tDCS-treated and sham-treated groups.
To determine subjective improvement or deterioration after the intervention, the participants completed a Global Rating of Change (GRC) scale. Changes in driver performance, countermovement jump (CMJ), GRC, and test of attentional interpersonal style (TAIS) from pre- to post-intervention were analyzed for each group.
Driver performance
To determine the driver performance, ball flight (carry), clubhead speed (CHS), and ball speed (BS) were measured using TrackMan 4 (TrackMan, Copenhagen, Denmark). The same club and ball were used during the measurements, and the average of five attempts after five practice sessions was used as the final value [20].
CMJ
The CMJ test is a simple method for measuring lower extremity muscle power. CMJ was measured using a Jumping Meter (TKK-5406; TAKEI, Japan). The test position involved standing upright and jumping vertically with a quick preceding squat, and the maximum height of the jump was measured. The test was performed twice with a rest period of approximately 3 min between each test. Each trial was separated by a 60-s rest interval to minimize movement-related fatigue [21].
GRC scale
The GRC scale was used to determine the subjective improvement or deterioration of golf performance after warm-up, including tDCS application. The GRC scale includes the question, “After tDCS treatment and warm-up, did your subjective perceived motor performance improve or deteriorate when performing the golf swing?,” which was answered by the participants using a scale of -5 to +5. The score was used as the outcome [22].
TAIS
The shortened form of the TAIS developed by Nideffer [23] was used to measure attention. The six subscales are broad external focus (BET), overload of external stimuli (OET), broad internal focus (BIT), overload of internal stimuli (OIT), narrow attention (NAR), and reduced attention (RED). Higher scores on the BET, BIT, and NAR indicate positive attentional traits, whereas higher scores on the OET, OIT, and RED indicate negative attentional traits. The scale consisted of 12 items, two for each factor, and was scored using a five-point Likert scale [22].
Intervention
tDCS
tDCS was performed using a Halo Sports 2 headset (Halo Neuroscience, San Francisco, CA, USA). Three electrodes (primers) were wetted with saline and positioned over the anterior parts of the frontal and temporal lobes, including the primary motor areas. A stimulus of 1.98 mA was applied for 20 min, according to the manufacturer’s instructions. The sham group used the same equipment and protocol as the tDCS group and involved blocking the current so that the participants could not be aware of it [8,24].
Warm-up program
The warm-up program used in this study was modified and supplemented based on a previously validated and effective program [25]. To investigate the effects of tDCS, warm-up exercises were performed while wearing a headset and the groups were distinguished based on whether the current was applied or impeded. The warm-up program is presented in Table 2.
Warm up program.
Statistics
Descriptive statistics (mean and standard deviation) were calculated using SPSS/PC 25.0, a statistical program for Windows, and repeated measures analysis of variance was used to compare the timing of tDCS application between the groups. Statistical significance was set at p<0.05.
RESULTS
Differences in golf performance between groups following tDCS application
In the analysis of the changes in golfers’ driver performance following tDCS, statistically significant differences were found in the timing of flight distance (carry) (p<0.001) and interaction effect (p<0.001), timing of CHS (p<0.001) and interaction effect (p<0.05), and timing of BS (p<0.01) and interaction effect (p<0.05), with no differences between groups.
Driver shot performance.
GRC scale (global rating of change scales).
CMJ (countermovement jump).
Differences in GRC scale between groups following tDCS application
Significant differences were found in the time (p<0.001), group (p<0.01), and interaction effects (p<0.01) when analyzing the differences in GRC scale scores during the driver swing following tDCS.
Differences in CMJ between groups following tDCS application
Significant differences were found in the timing (p<0.001) and interaction effects (p<0.01) when analyzing the differences in CMJ following tDCS; however, no significant differences were found between the groups.
Differences in TAIS between groups following tDCS application
Analysis of the differences in TAIS following tDCS revealed significant differences in the timing of the BET (p<.05) and NAR (p<.05), whereas OET, BIT, OIT, and RED did not show significant differences in the timing, group, and interaction effects.
DISCUSSION
College athletes need to be time-efficient due to their various activities such as studying, training, and participating in competitions. Previous studies have reported improved concentration and exercise performance with tDCS, and it is believed that tDCS can be easily applied and efficiently provided in training programs. This study aimed to determine the effects of warm-up with tDCS on performance factors in golfers and to provide scientific evidence on the effectiveness and methods of applying tDCS to warm-ups in golfers. tDCS may play a role in improving sports performance by promoting corticospinal tract activation and strengthening entire motor pathways [26]. Favorable outcomes have been demonstrated when tDCS is used in combination with active exercise. When anodal tDCS (2 mA, 0.08 mA/cm2) is combined with exercise, the amplitude of motor excitability increases two-fold compared with that of tDCS or exercise alone [27]. Previous studies have shown that motor cortex excitement increases by 150% compared with the baseline for up to 90 min after applying tDCS [28].
TAIS (test of attentional and interpersonal style).
The driver distance, clubhead speed, and ball speed following tDCS application revealed significant differences in the timing and interaction between the groups. In golf, driving distance and clubhead speed have been reportedly associated with lower extremity strength and power, and upper extremity power [29, 30]. Lu et al. [31] conducted a study on 19 healthy young men who were subjected to 20 min of real tDCS (2 mA) or sham (0 mA) over the primary motor cortex (M1) on different days. They found that tDCS improved muscle strength and power in non-dominant knee flexion-extension. Similarly, a recent meta-analysis analyzed the effect of tDCS and reported increased strength in isometric contractions with a single application [32], which was attributed to increased motor cortex excitation and decreased short-interval intracortical inhibition [5].
The GRC scale is a quick and simple method for determining the amount of change in response to an intervention. In this study, the subjective impact and effectiveness of tDCS warm-up were examined and found to be significant for both the tDCS and sham groups in terms of the time and interaction effects, with no differences between the groups. These results suggest that the short duration of the novel treatment may have had some placebo effect on the athletes and that the warm-up itself may have affected them. A previous study that examined changes in GRC scale scores before and after tDCS application in archery players found no statistical difference [40]. This is believed to be due to participants’ negative preoccupation with short-term effects, as the nature of the GRC is subjective.
The ability to control muscles and achieve maximum speed and power is critical in many sports [33]. In particular, jumping performance requires upper and lower body coordination, motor unit mobilization, strength and stability, and the interaction of each system [34]. Recently, CMJ has been used to measure fatigue levels and agility in athletes. For elite athletes, the ability to optimize muscle control and maximize speed, power, and endurance is critical, as are training and motivation [33].
In this study, CMJ outcomes did not differ between the tDCS and sham groups; however, a significant difference was found between the time periods. A recent study by Kim et al. [35] applied tDCS to 30 soccer players (15t DCS and 15 sham players) for 6 weeks. Dynamic stretching was performed with tDCS application for 20 min. They reported a significant effect of dynamic stretching combined with tDCS on the jump performance of soccer players, supporting the results of this study. This may be partly due to the effect of dynamic stretching, and tDCS application may have maximized the effect of motor cortex stimulation. Previous studies have reported differences in quadriceps muscle activity between tDCS and sham groups in female soccer players [36], improvements in dynamic balance following tDCS in healthy adults [37], and a 4% increase in maximal power output during maximal cycling exercises following tDCS [38]. Considering the results of these studies, the effectiveness of tDCS in the medium and long term should be verified for its incorporation into athletic training programs.
Previous studies using tDCS reported significant results in sports that require elevated levels of concentration, such as archery and shooting. Direct stimulation of the cerebral cortex using tDCS has been shown to effectively improve motor learning and concentration [39]. However, a previous study on elite archers subject to tDCS did not show changes in concentration [40]; similarly, this study did not show significant differences in concentration. Therefore, it is necessary to further verify the effects of tDCS on variables related to concentration in the mid- to long-term period.
This study aimed to verify the effect of warm-ups using tDCS on performance-related factors in golfers and to suggest the effective application of tDCS.
The results of this study showed that warm-up with tDCS had positive effects on carry (p=.004), CHS (p=.019), BS (p=.017) of driver performance, CMJ (p=.002), and GRC (p=.005); however, no significant difference was found in TAIS, which suggest that the warm-up with tDCS showed significant effects on driver performances, CMJ, and GRC.
Future studies should verify the effectiveness of tDCS independently and provide new alternatives for improving performance through its application in various aspects, such as training and pre-competition.
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant funded by Korea (MSIT) (No. 2022S1A5B5A17038433).