Effect Of Caffeine On Exercise Performance: Current Review

Abstract

Caffeine is an ergogenic supplement that has been attracting attention in the sports community for many years. It has been proven in many studies that coffee consumption has a positive effect on exercise performance. This study was conducted to (I) examine the effects of caffeine on exercise performance and different performance areas, (II) to provide comprehensive recommendations on the use of caffeine in sports and exercise, and (III) to identify existing gaps in the literature and to make key recommendations for future research. This current review article provides an analytical view of studies involving the use of caffeine for the physical, physiological, and cognitive performance of individuals, and discusses factors that may affect the ergogenic effects of caffeine on the different proposed activities. Within the scope of this review, previously published studies were searched using comprehensive keywords related to "caffeine" through "ELSEVIER Science Direct (SciVerse), Taylor & Francis, EBSCOhost-Academic Search Complete, PubMed and SpringerLink, Google Scholar" databases until January 2021. As a result, it has been reported that caffeine increases endurance performance by 2-4% and improves short-term and intense intensity exercise performance in highly trained individuals. The improving effect of caffeine on cognitive performance supports the use of caffeine as an ergogenic supplement. Caffeine has been shown to increase sympathetic nervous system activity and release fatty acids from adipose and / or intramuscular stores. This mechanism, which occurs indirectly through increased adrenaline levels, has the potential to increase the availability of fatty acids for oxidation and the resting metabolic rate. At the same time, it has been observed that caffeine does not cause dehydration and is a reliable ergogenic supplement in this respect. The ergogenic effect of caffeine should be clarified by focusing on questions such as at what time of the day caffeine consumption affects caffeine ergogenicity, the effect of age on caffeine ergogenicity, caffeine intake according to athlete's training level, and the importance of genotype in terms of caffeine consumption.

Full text

Effect Of Caffeine On Exercise Performance: Current
Review
Yusuf BUZDAĞLI1A, Aslıhan TEKiN2B ,Erdinç ŞIKTAR1C, Günay ESKiCi3D
1Department of Physical Education and Sport, Faculty of Sport Sciences, Erzurum Technical University, Erzurum, Turkey
2Nutrition and Dietetics Department, Graduate School of Winter Sports and Sport Sciences, Ataturk University, Erzurum, Turkey
3Department of Coaching Education, Faculty of Sport Sciences, Çanakkale Onsekiz Mart University, Çanakkale, Turkey
Address Correspondence to Y. Buzdağlı: e-mail: yusuf.buzdagli@erzurum.edu.tr
(Received): 12/03/2021/ (Accepted): 30.04.2021
A:Orcid ID: 0000-0003-1809-5194 B:Orcid ID: 0000-0002-1760-5378 C:Orcid ID: 0000-0003-0387-3969 D:Orcid ID: 0000-0002-4349-4704
Abstract
Caffeine is an ergogenic supplement that has been attracting attention in the sports community for many years. It has been
proven in many studies that coffee consumption has a positive effect on exercise performance. This study was conducted to (I)
examine the effects of caffeine on exercise performance and different performance areas, (II) to provide comprehensive
recommendations on the use of caffeine in sports and exercise, and (III) to identify existing gaps in the literature and to make
key recommendations for future research. This current review article provides an analytical view of studies involving the use
of caffeine for the physical, physiological, and cognitive performance of individuals, and discusses factors that may affect the
ergogenic effects of caffeine on the different proposed activities. Within the scope of this review, previously published studies
were searched using comprehensive keywords related to "caffeine" through "ELSEVIER Science Direct (SciVerse), Taylor &
Francis, EBSCOhost-Academic Search Complete, PubMed and SpringerLink, Google Scholar" databases until January 2021. As
a result, it has been reported that caffeine increases endurance performance by 2-4% and improves short-term and intense
intensity exercise performance in highly trained individuals. The improving effect of caffeine on cognitive performance
supports the use of caffeine as an ergogenic supplement. Caffeine has been shown to increase sympathetic nervous system
activity and release fatty acids from adipose and / or intramuscular stores. This mechanism, which occurs indirectly through
increased adrenaline levels, has the potential to increase the availability of fatty acids for oxidation and the resting metabolic
rate. At the same time, it has been observed that caffeine does not cause dehydration and is a reliable ergogenic supplement in
this respect. The ergogenic effect of caffeine should be clarified by focusing on questions such as at what time of the day
caffeine consumption affects caffeine ergogenicity, the effect of age on caffeine ergogenicity, caffeine intake according to
athlete's training level, and the importance of genotype in terms of caffeine consumption.
Keywords: Caffeine, Exercise, Athletic performance
INTRODUCTION
Caffeine is the world's most consumed
psychoactive substance, naturally found in many
plant species, including coffee, tea, and cocoa.
Caffeine, which is added to many beverages such as
energy drinks and whose consumption has
increased day by day in the last two decades, is
mostly consumed in the form of beverages such as
coffee, soft drinks, and tea (1). In Western countries,
approximately 90% of adults consume caffeine
regularly, while daily caffeine consumption in US
adult men and women is estimated to be 200 mg,
according to 2009-2010 data (2, 3).
Caffeine is one of the most popular socially
acceptable ergogenic supplements that has been
used in athletic circles as an ergogenic aid or
performance enhancer for years, because it is not
doping and can be taken from natural sources. It is
also a supplement with a long history of use for its
ergogenic effects on performance. Caffeine intake
has been very common among athletes, especially
since 2004, when the World Anti-Doping Agency
Turkish Journal of Sport and Exercise /Türk Spor ve Egzersiz
Dergisi
http://dergipark.gov.tr/tsed
Year: 2021 - Volume: 23 - Issue:1 - Pages: 86-101
DOI: 10.15314/tsed.895754
ISSN: 2147-5652
https://dergipark.org.tr/tr/pub/tsed

Yusuf BUZDAGLI Orcid ID: 0000-0003-1809-5194 / Aslıhan TEKiN Orcid ID: 0000-0002-1760-5378 / Erdinç SIKTAR Orcid ID: 0000-0003-0387-3969 / Günay ESKiCi Orcid ID: 0000-0002-4349-4704
Turkish Journal of Sport and Exercise /Türk Spor ve Egzersiz Dergisi 2021; 23(1): 86-101 87
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was removed from the in competition prohibited
substances list. For example, 74% of urine samples
collected between 2004 and 2008 and analyzed as
part of doping control contained caffeine (4). Given
the inconsistent evidence from primary research
examining the effects of caffeine on exercise
performance, several research groups have explored
this issue using meta-analytical methods (5-8) .
While these meta-analyzes generally report the
ergogenic effects of caffeine on exercise
performance, current studies should not focus solely
on the effect of caffeine on exercise performance; He
suggested that attention should also be paid to
cognitive performance, caffeine use dosage and
intake forms, fat metabolism, combined intakes of
caffeine, caffeine consumption habits and effects on
dehydration. Although many studies are
investigating the effects of caffeine on overall health
and exercise performance, recent research has
shown that caffeine not only affects exercise
performance, but also metabolic disorders, cognitive
performance, consumption amount and forms, fat
metabolism, combined intakes, caffeine
consumption habits, and dehydration. It emphasizes
the need to focus on the effects of caffeine (5, 9).
Responses in the organism with caffeine intake
may vary from person to person. A person’s genetic
structure, consumption amount, individual's
performance goal, type of sport performed, placebo
effect, and caffeine intake form can affect the result.
In addition, the health effects of caffeine have long
been a topic of interest, and as noted by extensive
research, caffeine remains an important dietary
component for public health. It has also become
ubiquitous in the sports world, where there is
intense interest to better understand the effect of
caffeine on various exercise performance. Thus,
caffeine has been the focus of attention in the field of
ergogenic aids and sports supplement research in
recent years.
The purpose of this review is to reveal many
aspects of caffeine's effect on exercise performance.
In this direction, the results of the research on
aerobic/anaerobic performance, strength/power
performance, consumption amount and time,
combined forms, caffeine consumption habits, and
dehydration were evaluated and suggestions were
made on the subject.
METHOD
Within the scope of this review, previously
published studies were scanned through "ELSEVIER
Science Direct (SciVerse), Taylor & Francis,
EBSCOhost-Academic Search Complete, PubMed
and SpringerLink, Google Scholar" until January
2021, "caffeine and exercise" for search, the
keywords "caffeine and aerobic performance",
"caffeine and resistance exercises", "caffeine and
anaerobic performance", "caffeine and cognitive
performance", "caffeine and supplements", "caffeine
and dehydration", "caffeine consumption forms",
"caffeine and doping", "caffeine metabolism",
"caffeine and fat metabolism", "caffeine and doping",
and "caffeine and consuming habits" were used.
Caffeine Metabolism
Caffeine is a purine alkaloid containing the
methyl group at the 1,3,7 position, also called
trimethylxanthin, and has a stimulating effect on the
central nervous system (CNS). As a food additive, it
can be produced synthetically for use in dietary
supplements and pharmaceutical preparations
where synthetic caffeine is the same as intrinsic or
plant-derived caffeine. It has been defined as the
most commonly consumed pharmacologically active
food in the World (10).
Most of the biological effects of caffeine at the
levels reached during normal consumption are due
to its antagonizing the adenosine receptors,
particularly the A1 and A2A receptors, and to a
lesser extent the A2B and A3 receptors. A1 and A2A
adenosine receptors affect various mechanisms
found in large areas of the brain that are involved in
the regulation of sleep, arousal, and cognition.
Therefore, it is not surprising that caffeine as an
adenosine receptor antagonistcan alter physiological
and mental states. Central adenosine receptors
affected by typical caffeine exposure (11). Because
the caffeine molecule is chemically similar to the
adenosine molecule, it binds to adenosine receptors.
Since adenosine receptors are related to sleep, sleep
is not felt if caffeine is attached to the receptors
instead of adenosine. The sleep-disturbing effect of
caffeine is due to this antagonist mechanism.

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Figure 1. Chemical structures of caffeine and adenosine (12).
Caffeine is taken up and absorbed through food
or synthetically. Once absorbed, it reaches all body
cells. It then crosses the blood-brain barrier rapidly
and is metabolized by the liver's P450 1A2 (CYP1A2)
enzyme. Caffeine responses of individuals are
different due to polymorphism in the CYP1A2 gene.
After oral ingestion of caffeine, mostly in the form of
coffee or tea, 99% is absorbed into the bloodstream
from the gastrointestinal tract and peaks 30-60
minutes after eating. Caffeine absorption is between
45 and 80 minutes for caffeine-containing chewing
gum, and 85-120 minutes for caffeine-containing
capsules (13).
Figure 2. Main pathways in caffeine metabolism (12). Abbreviations: CYP1A2, cytochrome P450
1A2; CYP2A6, cytochrome P450 2A6; NAT2, N- acetyl transferase 2; XO, xanthine oxidase.

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Caffeine ergogenicity has effects on the muscle
that can directly contribute. The most likely way
that caffeine can benefit muscle contraction is
through calcium ion (Ca2+) mobilization, which
facilitates force generation by each motor unit (15-
17). Fatigue caused by the gradual reduction of Ca2+
release can be alleviated after caffeine intake (17, 18).
Similarly; Caffeine, partially increased
sodium/potassium pump activity (Na+/K+)
potentially increases the stimulation-contraction
matching required for muscle contraction (19).
Caffeine appears to use its effects in various parts of
the body, but the most solid evidence suggests that
the main target is in the CNS, which is now
considered the primary mechanism by which
caffeine alters mental and physical performance (20).
It is believed that caffeine exerts its effects on the
CNS through antagonism of adenosine receptors
and leads to increases in neurotransmitter release,
motor unit firing rates, and pain suppression (21-23).
Adenosine is involved in numerous physiological
processes and plays a very important role as a
homeostatic regulator and neuromodulator in the
nervous system. The main known effects of
adenosine are; It is to reduce the concentration of
many neurotransmitters in the CNS, including
serotonin, dopamine, acetylcholine, norepinephrine,
and glutamate. Having a molecular structure similar
to adenosine, caffeine binds to adenosine receptors
after ingestion and therefore increases the
concentration of these neurotransmitters (24, 25).
This has positive effects on mood, alertness, focus,
and mental vitality in most, if not all individuals (26-
28). Caffeine can be used effectively to manipulate
our mental state. It is widely consumed in the form
of coffee to get rid of sleepiness. People avoid coffee
consumption when they do not want their sleep to
be affected negatively.
Caffeine and Exercise
The ergogenic potential of caffeine has been
extensively studied in the sports and exercise
science literature dating back to 1907 (29). The effect
of caffeine on exercise performance can be listed as
follows (30).
Table 1. Caffeine Amounts of Some Foods and Beverages
Food/Beverages
Amount
Caffeine (mg)
Cafe Latte /Cappuccino
200 mL
126
Filter Coffee / Black Coffee
200 mL
130
Espresso
200 mL
388
Nescafe
200 mL
62
Turkish Coffee
100 mL
58
Brewing Bag / Black Tea
100 mL
21
Green Tea
100 mL
15
Herbal Tea
240 mL
0
Redbull
250 mL
80
Energy Drinks
330 mL
100
Coffee With Milk
250 mL
158
Dark Chocolate
50 g
50
Hazelnut Chocolate
50 g
3
Chocolate Bar / Nougat
50 g
3
Chocolate Sauce
20 g
6
Chocolate Bar
50 g
9

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Figure 3. Caffeine and Performance Relationship. : increased, : decreased
Effect of Caffeine on Aerobic Performance
Caffeine is an ergogenic aid preferred by
athletes or active individuals in a wide variety of
sports and activities involving aerobic endurance. A
positive effect on performance has been proven in a
variety of endurance sports, including cycling (31,
32), running (33, 34), cross-country skiing (35), and
swimming (36).
Studies show that caffeine intake (eg, 3-9 mg /
kg taken 30-90 minutes before exercise) can reduce
carbohydrate use during exercise, thereby increasing
endurance exercise capacity (37). In a study
involving 8 trained cyclists and triathletes
accustomed to consuming low doses of caffeine
(≤300 mg / day), participants consumed beverages
consisting of caffeine (5 mg / kg), instant coffee (5
mg/kg caffeine), instant decaffeinated coffee or
placebo 1 h before exercise. The results of the study
found that both caffeine (5 mg / kg) and coffee (5mg
/ kg caffeine) consumed 1 h before exercise could
improve endurance exercise performance (38). In a
study conducted on cyclists, it was determined that
among those who consumed caffeinated coffee or
decaffeinated coffee (6 mg / kg) 60 minutes before
exercise, those who consumed caffeinated coffee had
a positive effect on performance (39).
Many studies have shown that caffeine intake at
the level of 3-6 mg / kg / day increases endurance by
2-4% (31, 32, 40, 41).
Effect of Caffeine on Anaerobic Performance
Anaerobic performance is a term of great
importance for sports branches that are completed
in a short time or require explosive force. Regular
trainings cause an increase in the anaerobic
performance of athletes. Athletes use a variety of
ergogenic supplements to further increase anaerobic
performance. Caffeine is of great importance in
these ergogenic supplements.
In a study of 21 well-trained male participants,
a gelatin capsule (30m; repeated at 35-second
intervals) containing caffeine (5 mg / kg) and
placebo (maltodextrin) taken 1 h before completing
a multi-sprint trial was found to have an ergogenic
effect on performance (42). In another study, it was
determined that caffeine improves repetitive sprint
performance but does not affect maximum strength
and fatigue (43). In a study conducted by giving
caffeine at a dose of 6 mg / kg to participants who
are not trained in a particular sport, it was found
that the maximal cycling speed of 2×60 seconds
increased (44). In studies investigating the effect of
caffeine given at the level of 5-6 mg / kg / day on
anaerobic power in non-training individuals, it was
found that performance did not change (45, 46) or
increased (47).
Considering the studies that summarize the
effectiveness of caffeine on short-term anaerobic
exercises, it is seen that the use of caffeine in such
exercises is less, and there is no consensus on the
results. Therefore, it seems that more studies need to
be performed on the relationship between caffeine
and short-term exercise. In general, although the
results are heterogeneous, it has been reported that
caffeine supplementation at doses of 4-6 mg / kg on
multiple and single sprint activities requiring high-
intensity effort significantly increases performance
in athletes with high training level while the same

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positive effect was not observed in participant
groups with low training level.
The Effect of Caffeine on Strength
Performance
Strength development through resistance
training is an important component of conditioning
programs for both fitness and competitive sports
and activities. The most common consumption form
preferred by individuals with or without training in
strength studies is caffeine taken at the level of 3-6
mg / kg (2-11 mg / kg) 90 minutes before exercise in
the form of pills or capsules. Although several
studies have been published by ISSN (International
Society of Sports Nutrition) since 2010, investigating
the effects of caffeine on strength performance (48),
some uncertainties persist in the performance
enhancing effect of caffeine in activities involving
muscle endurance, strength, and power.

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Table 2. Investigations examining the effects of caffeine on exercise performance
References
Participants
Exercise Protocol
Cafe Dose
Conclusion
Grgic J et al.
(49)
Resistance trained male (n=22)
1RM barbell bench press and leg
press and 60% at 1RM again until
exhaustion
6 mg / kg
 The total weight removed during the 60% 1RM trial was 11% and 12%
higher for bench press and leg press with caffeine compared to placebo
but still did not reach significance.
 The perceived intensity was similar to caffeine versus placebo at the
end of resistance exercise.
 Acute caffeine intake did not significantly alter muscle strength or
endurance during intense bench press or leg press exercise.
Norum M. et
al. (50)
Resistance trained female (n=15)
Squats, bench press,
countermovement jumps (CMJ) until
exhaustion at 60% 1RM
4 mg / kg
 *Caffeine significantly improved repetitions in squats and bench press
to exhaustion compared to placebo.
 *Caffeine significantly increased CMJ height and strength.
Goldstein E. et
al. (51)
Resistance trained female (n=15)
1RM barbell bench press and repeat
until exhaustion at 60% 1RM
6 mg / kg
 A significantly higher bench press maximum was seen with caffeine at
60% 1RM repeats with no significant difference between conditions.
 Systolic blood pressure was significantly higher after exercise with
caffeine.
Timmins TD
and Saunders
DH (52)
Resistance trained male (n=16)
Maximal voluntary contraction; The
isokinetic peak torque of knee
extensors, ankle plantar flexors,
elbow flexors and wrist flexors was
measured at an angular velocity of 60
° / s.
6 mg / kg
 Caffeine increased the maximal voluntary contractile strength in
resistance training men, regardless of the position of the muscle group.
 Although the improvement in peak torque increased according to
muscle group size, its effect was not clear.
Woolf K. et al.
(53)
High-level fitness male team athlete
(n = 18)
Leg press, chest press ve wingate testi
5 mg / kg
 With caffeine, the more total weight was lifted on the chest press and a
higher peak strength was achieved during the Wingate test.
 No difference was found between caffeine and placebo for average
strength, minimum strength, and power drop (Wingate test) on leg
press.
 Higher insulin and glucose concentrations were observed after exercise
with caffeine.
 Systolic blood pressure was significantly higher after exercise with
caffeine.
 No difference was found between caffeine and placebo for free fatty
acid concentrations, plasma lactate concentrations, cortisol
concentrations, heart rate, and perceived intensity.
Beck TW. et al.
(54)
Resistance trained male (n=31)
1RM bench press power and time to
exhaustion at a speed corresponding
to 85% of VO2max
201 mg (2.1-3 mg /
kg)
 It was observed that caffeine did not contribute to the exercises.
Wilk M. et al.
(55)
Male bodybuilding with caffeine
habits (n = 16)
1RM strength test, muscle endurance
at 50% 1RM
9-11 mg / kg
 It was observed that high-dose acute caffeine supplementation did not
increase muscle strength or muscle endurance in athletes with caffeine
habits.
Trevino MA.
et al. (56)
Recreatively active male (n = 13)
3 maximum isometric muscle
movements of the elbow flexors
5-10 mg / kg
 It was observed that caffeine supplementation did not provide an
ergogenic effect for elbow flexors during isometric muscle movements.

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Astorino TA.
et al.(38)
Resistance trained male (n=22)
1RM bench press and leg press,
repeat until it is exhausted at 60%
1RM
6 mg / kg
 Bench press and leg press 1RM, there was no significant increase in
caffeine-boosted participants.
Glaister M. et
al.(42)
Well-trained male (n = 21)
Multiple sprint test consisting of
12×30 m straight-line sprints repeated
at 35 second intervals
5 mg / kg
 Caffeine has been shown to have ergogenic properties with the
potential to benefit performance in both single and multiple sprint
sports.
Trexler ET. et
al.(43)
Well-trained male (n = 21)
Single reps for leg press and bench
press at 80% of 1RM and repetitions
to fatigue at 1RM
300 mg (powder)
303 mg (coffee)
 It has been observed that caffeine can improve repetitive sprint
performance.
 It was observed that caffeine did not affect repetitions for maximum
strength and fatigue using both upper body and lower body exercises.
Crowe MJ. et
al. (44)
Untrained male (n = 12), Untrained
female (n = 5)
2 × 60 seconds maximal cycling
6 mg / kg
 It was observed that peak power was reached in a shorter time in the
second of 2 × 60 seconds maximal cycling.
Collomp K. et
al. (45)
Untrained male participating in
non-specific sports activities only 2-
3 h per week (n = 3), untrained
female participating in non-specific
sports activities only 2-3 h per week
(n = 3)
30-second wingate test
5 mg / kg
 *Caffeine did not appear to cause a significant increase in performance
for peak power or total work load.
Greer F. et al.
(47)
Recreatively active male (n = 9)
30-second wingate test (2 separate
sections, 4 minutes interval)
6 mg / kg
 The last two of the four wingate test showed a decrease in strength
compared to the placebo.
 Caffeine did not appear to have a significant effect on blood lactate, O2
consumption, or aerobic additives at any time during the protocol.
 No ergogenic effects of caffeine on power output were observed during
repetitive periods of short intense exercise.
Lorino AJ. et
al. (46)
Untrained male (n = 16)
Agility run and 30-second Wingate
test
6 mg / kg
 Caffeine did not seem to provide significantly better performance for
agility running and the 30-second wingate test.
Bold text associated with reported trial outcomes; * delineates a significant change,  = no improvement/change, ↑ = improved performance, ↓ = decreased, 1RM = repetitive maximal,
VO2max = maximum oxygen consumption

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Forms of Caffeine
Although caffeine is often taken through
beverages such as tea and coffee, it can be consumed in
different forms to examine its effect on sports
performance and to be consumed most beneficially.
Caffeine in athletes; caffeinated bars and gels,
caffeinated chewing gum, caffeinated energy drinks,
caffeinated nasal and mouth aerosol sprays, and
caffeinated mouthwashes.
Studies show that bars and gels containing 100 mg
of caffeine improve cognitive function, exhaustion
time, and time trial performance. Although plasma
caffeine measurements are lacking in these studies, it
can be assumed that the increases will mimic the
findings obtained from caffeine tablet and coffee
consumption (57-60). Since caffeinated bars and gels
are key sources of caffeine for athletes during training
and competition, and there are currently no studies
examining female participants, more research is
needed in this area. Studies show that caffeine in
chewing gum at a dose of 200-300 mg is ergogenic
when given before or during an endurance exercise in
well-trained women and male cyclists (61). Current
literature does not support the ergogenic effects of
caffeine supplements administered in the form of
energy drinks. However, additional studies are needed
to examine the effectiveness of individual components
of caffeinated energy drinks on performance (62).
The consumption of caffeine in the form of mouth
and nasal sprays enables the stimulating physiological
effect to begin very quickly. Caffeine is poured into the
person's tongue in combination with a carrier and a
breath freshener, as a liquid spray or directly into the
person's tongue. It is rapidly absorbed from the
intestinal buccal membrane. It has been suggested that
caffeine mouthwash exerts its ergogenic effects by
allowing caffeine molecules to bind to adenosine
receptors in the mouth and inhibit adenosine
competitively (63, 64). This interaction is thought to
increase the permeability of the buccal mucosa and
thus trigger caffeine absorption into the bloodstream
(65). Another mechanism of action is mentioned to
explain the performance benefits associated with
caffeinated mouthwash. The oral cavity is decorated
with bitter taste receptor cells, especially found in the
oropharyngeal epithelium, and these have been shown
to be activated when exposed to caffeine. It has been
suggested that activation of these bitter taste receptors
can activate taste neural pathways and ultimately
stimulate brain regions associated with information
processing and reward. Although it has been reported
that caffeinated aerosol mouth and nasal sprays can
stimulate nerves with direct brain connections and
enter the blood through mucosal and pulmonary
absorption, research on this condition is scarce (62).
The Effect of Caffeine on Cognitive Performance
For centuries, caffeine, usually taken in the form of
coffee or tea, has been a popular tool for enhancing
various aspects of mental or cognitive functions (28). In
addition to exercise performance; Continuous cognitive
function is also important because of the routine work
requirements of caffeine. Although there is widespread
scientific work on the behavioral effects of caffeine,
some details regarding specific functional aspects
remain controversial (66). While there is a general
consensus that caffeine improves “lower” cognitive
functions such as simple reaction time, the effects of
caffeine on “higher” cognitive functions such as
problem solving and decision making are often
debated. This is partly because there are fewer
published studies of higher-level cognitive function
and the available ones differ greatly from the methods
used (67).
Caffeine increases arousal in a dose-dependent
manner; low doses can improve hedonic tone and
reduce anxiety, while high doses can increase
symptoms of anxiety, irritability, and tension (68). How
caffeine affects performance depends in part on the
level of arousal of the individuals studied, particularly
the extent to which the participants were sleep
deprived or how tired or well rested. One study
evaluated the classic inverted-U hypothesis in terms of
caffeine to what extent stimulation improves or impairs
performance (69). According to the Yerkes-Dodson
law, there is an empirical relationship between arousal
and performance, such that low arousal is associated
with poor performance, while increased physiological
or mental arousal is associated with improved
performance, but only to a range (70). When the
arousal level increases too much, performance
decreases. Thus, the individual's pre-dose arousal level
before consuming caffeine will affect the effects
observed (71). Giving a large dose of caffeine to a
person who is seriously tired will improve
performance because in this case caffeine promotes an
appropriate level of arousal (i.e., caffeine advances the
individual's stimulation towards the middle range of
the Yerkes-Dodson curve). Conversely, giving the same
dose to someone who is already well rested and highly
aroused may decrease rather than improve
performance because in this case caffeine produces an
over-arousal state that will impair cognition according
to the Yerkes-Dodson law (72).

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Table 3. Investigations examining the effects of caffeine on cognitive performance
References
Participants
Cafe Dose
Conclusion
Brunyé TT. et al. (67)
University student male (n = 16) and
female (n = 20)
100 mg
200 mg
400 mg
 It was observed that caffeine improved participants' skills to use warning cues efficiently and to avoid the
impact of information incompatible with the action.
 Caffeine has been shown to improve performance in tasks that require constant attention and attention.
 It has been observed that caffeine has different effects on visual attention networks as a function of dose, and
these effects have implications for the interactions of caffeine, adenosine and dopamine in the brain areas that
direct visual attention.
Hogervorst E. et
al.(58)
Well-trained cyclist male (n = 24)
100 mg
 It was observed that caffeine increased speed in Rapid Visual Information Processing Tests.
 It was seen that complex cognitive ability increased significantly.
Antonio J. et al.(73)
In training men (n=11), in training
women (n=9)
4 mg/kg
 The energy drinks psychomotor vigilance ensured a shorter average reaction time.
 Caffeine significantly improved psychomotor alertness performance, a constant attention task.
McLellan TM. et al.
(74)
Soldier ((n=31)
200 mg
 Continuous alertness was maintained in the control, observation and exploratory vigilance task.
McLellan TM. et al.
(75)
Soldier (n=20)
600 mg
 It was observed that the alertness increased.
Kamimori G. et al.(76)
Special Forces Operators (n=20)
4×200 mg
 It was observed that the response speed increased during sustained psychomotor speed, enhanced event
perception, the number of correct responses to stimuli, and logical reasoning tests.
 No changes were observed in gun shooting.
Tikuisis P. et al.(77)
Soldier (n=20)
400 mg
100 mg
 There was an increase in the cognitive component of the gun shooting mission.
Zhang Y. et al.(78)
Fireman (n=10)
400 mg
 No changes were observed in perceived difficulty, mood reaction time, short-term memory and recall
memory.
Share B. et al.(79)
Elite sniper male (n=7)
2 mg / kg
4 mg / kg
 No difference was observed in shooting accuracy, response time, or target tracking time between groups.
Stuart GR. et al. (80)
Competitive Rugby players male
(n=9)
6 mg / kg
 There was a significant increase in correct passing ability.
Karayigit, R. et al. (81)
Female athletes (n=17)
3 mg / kg
6 mg / kg
 Caffeine has been shown to improve cognitive performance.
Khcharem A. et al.(82)
Recreational running (n=10)
5 mg / kg
 Caffeine was cognitively processed by applying the correct fine after complete sleep deprivation.
 Caffeine has been shown to affect cognitive performance by reacting after complete sleep deprivation.
Bold text associated with reported trial outcomes; * delineates a significant change,  = no improvement/change, ↑ = improved performance/change, ↓ = decreased, 1RM = repetitive maximal,
VO2max = maximum oxygen consumption

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Caffeine and Fat Metabolism
The list of supplements that claim to increase or
improve fat metabolism is long; The most popular
supplements include caffeine, carnitine, green tea,
conjugated linoleic acid, forskolin, chromium, seaweed,
and fucoxanthin (83). Much of the interest in caffeine's
effects on metabolism stems from exercise physiology
studies in the 1970s. Early research by Costill et al.
Showed that taking caffeine (coffee and pure caffeine)
before a workout significantly increases fat oxidation
rates and performance (84). Essig et al. also reported a
shift in substrate metabolism from carbohydrate to fat
during exercise following caffeine intake, accompanied
by a slight increase in serum plasma fatty acid
concentrations (85). The theory is that caffeine activates
fat and preserves muscle glycogen, resulting in
increased performance. Later, these two effects
separated from each other and it was reported that the
ergogenic effect of caffeine was mostly due to central
mechanisms. Thus, caffeine has been shown to increase
sympathetic nervous system activity and release fatty
acids from adipose and / or intramuscular stores. This
mechanism, which occurs indirectly through increased
adrenaline levels, has the potential to increase the
availability of fatty acids for oxidation. Caffeine also
has a direct effect on lipolysis. Acheson et al found that
administration of high doses of caffeine (8 mg / kg)
significantly increased the resting metabolic rate (RMR)
[20 kJ / (m2*h)] within 3 h after eating (86). Dulloo et al.
reported that even low doses of caffeine (100 mg) have
the potential to cause a thermogenic effect at rest. Over
a period of 150 minutes, RMR increased by 3-4% in
both lean and obese individuals. In the same study, the
RMR (8-11% increase) was further increased when
caffeine was taken at repeated doses (2 h intervals over
12 h) (87). It is not known whether this increase is due
to increased fat oxidation, increased carbohydrate
oxidation, or both. It has been emphasized before that
the finding that caffeine can increase fat oxidation is
not new. Although there are a few studies that support
this result, there are also studies showing that the cafe
does not affect on fat oxidation. These results, on the
other hand, spoil a general opinion on the subject. The
different results can be explained by the exercise
intensity or the participant population used in the
studies.
Caffeine and Hydration
Dehydration refers to an imbalance in fluid
dynamics (water and electrolyte balance) when fluid
consumption fails to meet the needs of our body (88).
In a study where participants exercised at 70-75%
VO2max until their self-determined exhaustion,
participants were given 5 mg / kg caffeine 2 h and half
an h before exercise, followed by 2.5 mg / kg caffeine,
respectively. There was no difference in dehydration in
the caffeine group compared with placebo (89). In a
study, just before running exercise, participants
completed the 10-second mouthwash protocol with 300
mg of caffeine or placebo diluted in 25mL of water, and
caffeine mouthwash did not change hydration status or
sweat rate after a 10km run (90). In a study examining
the effects of caffeine at different ambient temperatures
(12 and 33°C), participants who performed endurance
cycling exercises were provided 3 mg / kg of caffeine 60
minutes before and after exercise. Sweating rates
differed between 12 and 33°C, but no difference was
observed when comparing caffeine versus placebo (91).
In addition, when the ISSN's review on caffeine and
performance, published in 2010, was examined, it was
observed that there was no change in urine and blood
volume during the resting period, and the amount of
sweat during exercise was not different in both cases
(48). In a study of 50 men who drink coffee regularly,
there was no difference in the volume of urine
produced over 24 h, despite caffeine intake of 240 mg
or more per day. In this study, participants consumed
4x200 ml of water and coffee containing 4 mg / kg of
caffeine for 3 days (doses ranged from 204 to 453 mg of
caffeine). Post-study data also revealed that there was
no difference between the two groups for blood and
urine markers of measured hydration level (92).
Indeed, when caffeine intake is 200-450 mg or 2.5-4 mg
/ kg per day, there is no diuretic effect due to caffeine
consumption. It should also be remembered that
people who do not drink coffee regularly or have not
had coffee for a certain period of time are more likely
to temporarily respond to caffeine. On the other hand,
regular caffeine intake develops a higher tolerance to
the diuretic effect, even at higher doses.
The Effect of Caffeine Consumption Habit on
Performance
Quantifying habitual caffeine intake is difficult to
quantify, which is problematic for studies aiming to
compare performance results following habitual
caffeine intake with unconventional caffeine users. This
concern is highlighted by reports that vary widely in
the caffeine content of commonly consumed beverages.
Taking into account the daily caffeine intake of all
subjects enrolled in a given study is the standard
procedure for a research protocol. The purpose of
determining such dietary information is to determine
whether caffeine consumption has an effect on
performance and whether this result is different
between a person who regularly consumes caffeine or
not. Bell et al. Studied the effect of moderate doses of
caffeine on subjects defined as the user (300 mg / day)
and non-user (50 mg / day). The results showed an
increase in performance for both groups; however, the

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effect of supplementation lasted approximately three h
longer in subjects identified as non-users (93).
Similarly, in a study describing caffeine habits among
participants, there was no statistical difference for
VO2max between groups (participants participated in
a boost exercise protocol), but there was a significant
difference in ventilation and heart rate for people who
did not habitually caffeine at rest (94). In addition,
another study reported no significant difference
between caffeine users and those who did not, except
for an increase in plasma epinephrine during exercise
for caffeine naïve subjects compared with placebo (95).
Optimal Timing of Caffeine Supplement
Because plasma caffeine levels typically peak
within 60 minutes of intake (96, 97), the timing of
caffeine consumption relative to exercise should be
considered. In a study where a 40 km time trial
performance was performed, participants were given 6
mg / kg of caffeine 1 h before or just before exercise.
Caffeine consumed 60 minutes before exercise resulted
in significant improvements in the 40 km trail
performance. The ergogenic effect of caffeine was
found to be unrelated to the highest concentration of
caffeine in the blood at the start of endurance exercise
(98). In a study in which caffeine was provided in the
chewing gum at 75% VO2max 5 minutes, 60 minutes,
and 120 minutes before 15 minutes of cycling exercise,
caffeine applied in the chewing gum increased
performance when applied immediately before, not 1
or 2 h before exercise (61). In a study conducted to
examine the effect of caffeine supplementation on
cycling performance of 3 km more, at what time of the
day it occurred, it was observed that caffeine was more
effective in exercise performed before 10:00 than in
exercise performed after 10:00. The greater
effectiveness of caffeine in the morning may be
attributed to the higher activity of the CYP1A2 enzyme
in the morning than in the evening (99). In a study to
determine the optimal timing of caffeine intake,
participants were provided with 6 mg / kg of caffeine
30 minutes, 60 minutes, and 120 minutes before
exercise. Caffeine timing before exercise provided the
most consistent ergogenic benefits 1 h earlier compared
to other time points, especially compared to 2 h (100).
One study in which 5 mg / kg of caffeine was provided
1 h, 3 h, and 6 h before exercise concluded that the
increase in performance was seen only when caffeine
was taken 1 and 3 h before (93). In a study by Cox et al.,
6 mg / kg of caffeine was provided in capsule form 1 h
before exercise and six doses of 1 mg / kg caffeine every
20 minutes during exercise, with the significant
difference being achieved with caffeine taken before
exercise (101). Unlike other studies, in a study in which
low (100 mg) and medium (200 mg) doses of caffeine
were provided towards the end of the exercise, both
doses given late were found to improve performance
(102). Studies conducted for the optimal timing of
caffeine intake are inconsistent. The uncertainty of the
results may be due to the form of caffeine used, the
individual characteristics of the participants, and the
different caffeine consumption habits.
Caffeine and Doping
The World Anti-Doping Agency (WADA) explains
what substances considered doping are in its annual
statement. Until 2004, caffeine was also an ergogenic
aid that was considered among these substances.
However, WADA removed caffeine from the
prohibited list as of 2004. It has been shown that
caffeine supplementation in the 3-6 mg / kg range in
training athletes can significantly improve both
endurance and high-intensity performance. The
International Olympic Committee sets an allowable
limit for 12 µg of caffeine per ml of urine (103, 104).
Approximately one hour before the competition, the
caffeine dose in the range of 9-13 mg / kg will reach the
maximum urine concentration permitted for
competition (103). However, it should be kept in mind
that caffeine consumption and urine concentration are
dependent on factors such as gender and body weight
(105). Consuming 6-8 cups of coffee containing
approximately 100 mg of caffeine per cup results in the
maximum permissible urine concentration (104, 105).
According to The National Collegiate Athletic
Association, urine concentrations in excess of 15µg/ml
after the competition are considered illegal (106).
WADA, on the other hand, does not consider caffeine a
ban, but has included it in the list of must-watch in
athletic competition.
CONCLUSION
The scientific literature on caffeine supplements is
extensive. It is clear that caffeine is indeed ergogenic
for sports performance, but specific to the athlete's
condition, the intensity, duration, and type of exercise.
Therefore, after reviewing the available literature, the
following conclusions can be drawn:
• Caffeine is one of the most preferred ergogenic
supplements by athletes after being removed from the
prohibited list by WADA as of 2004.
• Caffeine makes the person feel more vigorous
thanks to the antagonist effect it creates with
adenosine.
Most of the studies have used a protocol in which
caffeine is taken 60 minutes before the performance to
ensure optimal absorption.

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• It has been observed that moderate (3-6 mg / kg)
caffeine intake contributes to sports performance in
strength / strength exercises and long-term exercises.
• In the studies conducted, caffeine; Its use in
caffeinated bars and gels, caffeinated chewing gum,
caffeinated energy drinks, caffeinated nasal and mouth
aerosol sprays, and caffeinated mouthwashes have
been shown to have additional benefit potential
depending on the type of exercise.
• When the effect of caffeine on cognitive
performance was examined, it was seen that 200-300
mg of caffeine consumption positively affected
cognitive performance, improved psychomotor
alertness reaction time, and mood.
• It has been observed that pre-exercise caffeine
consumption supports fat metabolism and increases
the use of fat as a substrate in energy metabolism, in
addition to increasing the resting metabolic rate.
• Scientific literature suggests that 2.5-4 mg / kg
caffeine intake does not cause diuresis, contrary to
what is known.
• While recommending caffeine supplements to
athletes, individual recommendations should be made,
keeping in mind that caffeine consumption habits may
affect the ergogenicity of caffeine.
• Caffeine supplementation at doses of 4-6 mg / kg
on multiple and single sprint activities requiring high
intensity efforts is suitable for use as it significantly
increases performance in athletes with high training
levels.
• Considering the positive effect of caffeine on fat
metabolism, it is appropriate to use it before exercise in
athletes who aim to lose weight and / or burn fat.
• The positive effects of caffeine supplementation
on cognitive performance can be evaluated particularly
in professions where cognitive alertness is important,
such as military personnel or firemen.
• In future studies, the ergogenic effect of caffeine
should be clarified by focusing on questions such as (I)
what time of the day caffeine consumption affects
caffeine ergogenicity, (II) what is the importance of
genotype in terms of caffeine consumption, (III) what is
the effect of age on caffeine ergogenicity, (IV) does
caffeine ergogenicity vary according to athlete's
training level.
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