Graduate Program in Department of Exercise Health Science, National Taiwan University of Sport
Phase: NA
Conditions: Caffeine, Placebo
Sponsor: National Taiwan Sport University

Caffeine supplementation improves the cognitive abilities and 
shooting performance of trained e-sports players 
 
 
Project summary 
We explored the effect of 3 mg/kg of caffeine supplementation on the cognitive ability 
and shooting performance of trained e-sports players. We recruited nine e-sports players 
who had received professional training in e-sports and had won at least eighth place in 
national-level e-sports shooting competitions. After performing three to five 
familiarization tests, we employed a randomized crossover design to divide participants 
into a caffeine trial (CAF) and a placebo trial (PL). The CAF group took capsules with 
3 mg/kg of caffeine, whereas the PL group took a placebo capsule. After a 1-h rest, the 
Stroop task, visual search ability test, and the shooting ability test were conducted. 
 
Introduction  
Owing to the popularity of e-sports, numerous countries have recognized e-sports 
as a formal sport. E-sports were also included as a demonstration event at the 2018 
Asian Games in Jakarta. Professional e-sports leagues have been founded in several 
countries. E-sports include multiplayer online battle field arena games (e.g., League of 
Legends), first-person shooter games (e.g., Counter-Strike: Global Offensive, and 
Valorant), real-time strategy games, and sports games (1). Studies on first-person 
shooters have revealed that players with experience in competitions had shorter reaction 
times in a Stroop test (2) and stronger visual search abilities (3). Therefore, improving 
cognitive abilities that relate to e-sports competitions may be critical for participants in 
first-person shooter competitions, and external nutrients that enhance cognitive abilities 
may be crucial to their success.  
 
Caffeine is a popular and effective ergogenic supplementation for athletes of all levels 
(4, 5). It is typically consumed through food and drink, and the mechanism through 
which low-dose caffeine acts as a psychostimulant is based on central antagonism at 
the A1 and A2A adenosine receptors. The capacity of caffeine to bind adenosine 
receptors facilitates the inhibition of the brake that endogenous adenosine imposes on 
the ascending dopamine and arousal systems,which facilitates cholinergic and 
dopaminergic transmission (6, 7). Therefore, caffeine consumption may improve 
energy, mood, cognitive function, attention, simple reaction time, choice reaction time, 
and memory and alleviate fatigue (8, 9). The consumption of caffeine 1 hour before 
playing a first-person shooter can improve players’ visual search ability and speed in a 
state of alertness (10). A dosage of 3 mg/kg of caffeine before a game can increase 

players’ typing speed (11), shorten their reaction times, and increase their shooting 
accuracy (12). However, few studies have explored this.  
 
Because visual search ability and the presence of decoys, which can distract 
players, can both affect play performance in first-person shooters, reaction time alone 
is insufficient as an index for cognitive ability in research on the effect of caffeine on 
shooting accuracy. We explored the effect of caffeine ingested 1 hour before a first-
person shooter on players’ performance by using a Stroop task and testing the players’ 
visual search and shooting abilities.  
 
 
Methods 
Participants 
We recruited nine healthy male adults (with the desired age and training). All 
participants had experience with national competitions and regularly underwent 
training in first-person shooters. They consumed less than 80 mg of caffeine a day and 
did not have any diseases affecting the heart, bones, and joints or diseases that preclude 
exercise. Before the experiment, all participants were fully informed of the 
experimental procedures and the possible risks, and they provided informed consent. 
This study received approval from the Institutional Review Board of Jen-Ai Hospital – 
Dali Branch (110-06). This study was conducted in accordance with the Declaration of 
Helsinki. 
 
Design 
 
We adopted a randomized crossover design and divided the participants into a 
caffeine trial (CAF) and placebo trial (PL). The order of the trails in a test was 
randomized, and tests were separated by 7 days to avoid interference. At least 1 week 
before the formal experiment, all participants participated in three to five 
familiarization tests, such as cognitive function tests and shooting tests. The primary 
outcome was cognitive function, and the secondary outcome was shooting performance.  
 
Experimental procedure 
 
All tests were conducted in a professional e-sports classroom, and the indoor 
ambient temperature was set at 26°C. Participants’ diet and meal times were recorded 
for the 3 days before the first experiment, and the participants were required to follow 
the same diet 3 days before the subsequent experiment. They were also required to 

avoid food and beverages with caffeine (e.g., coffee, energy drinks, chocolate, and tea) 
during this period. 
 
On the day of the formal experiment, participants had breakfast and lunch at 8:00 
a.m. and 12:00 p.m., respectively, and arrived at the classroom at approximately 3:00 
p.m. for the experiment. The participants took capsules with 3 mg/kg of caffeine (the 
CAFtrial) or a placebo capsule (the PLtrial) with 200 mL of water. The placebo capsule 
contained flour. Each participant had a computer with a frame rate of at least 240 Hz 
and a mouse of scrolling speed of 1 ms. After the participants remained in the room for 
1 hour, during which they were required to take a rest in any form of their choosing 
except engaging in esports, the Stroop task, visual search test, and shooting ability test 
were conducted.  
 
Outcome measure 
The color–word Stroop task and visual search test were conducted using Psych/Lab 
for Windows. Measures used in the literature with satisfactory reliability and validity 
were adopted. The Stroop task involved four base colors, namely red, green, blue, and 
yellow, and the names of the base colors were presented in Chinese characters and in 
various colors to confuse the participants. The participants were required to press a key 
corresponding to the base color name they saw on screen (“R” for red, “G” for green, 
“B” for blue, and “Y” for yellow). In each test, 80 trials lasting 5 min each were 
conducted. The test results comprised a congruent condition, in which the key pressed 
corresponded correctly to the color on screen, and an incongruent condition, in which 
the key pressed corresponded incorrectly to the color name on screen. 
 
In the visual search test, participants identified orange “T”s on the screen from 
upside-down orange “T”s, blue “T”s, and upside-down blue “T”s. When an orange “T” 
would appear, the participants were required to press the space bar as quickly as 
possible. If no orange “T” appeared, the participants were required to not react. A total 
of 80 search displays were presented in 5 min. In each display, 5, 10, 15, or 20 -Ts were 
presented.  
 
 
The shooting ability test involved a three-dimensional aim trainer, which was 
proposed in a previous study [12]. Participants used the mouse to shoot the electronic 
targets on the computer screen. The test comprised 60 targets and could be completed 
in 2 min. It was performed on a static map with medium difficulty. In each round, three 
targets appeared at once, and participants were required to shoot them within 2 s, ideally 
eliminating each target with a one-shot kill. Participants’ kill ratio (number of targets 

hit/60), hit accuracy (60/number of shooting), and average time to target were noted. 
 
Statistics 
All data are presented as averages ± standard deviations. The Shapiro–Wilk test was 
used to examine the normality of the data. Cognitive performance, accuracy, and hit 
reaction time were analyzed through a paired sample t test. We used G*power 3 
software24 to achieve an alpha value of 5% and a power of 0.8; a sample of six was 
considered sufficient for this study. All data were calculated using SPSS (version 20, 
Chicago, IL, USA), and the significance level was α < 0.05. 
 
 
 
 

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