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Rev Chil Nutr Vol. 44, Nº 3, 2017
ARTÍCULOS ORIGINALES
INTRODUCTION
Athletes are always looking for legal ergogenic aids to
increase their performance. Ergogenic aids are substances,
techniques, or sports equipment that improve sports
performance
1
. Among legal nutritional ergogenic resources,
we highlight caffeine (1,3,7-trimethylxanthine), which is one
of the most used ergogenic aids by athletes1-3. Del Coso et
al.
1
evaluated 20,686 urine samples from athletes of different
sports (i.e., handball, triathlon, cycling, rowing, athletics (track
and 2008. They found that 26.2% of the athletes presented
blood caffeine levels below 0.1 µg.ml-1 (limit of detection),
67.3% had below 5 µg.ml-1, and only 0.6% exceeded the
threshold of 12 µg.ml-1 (i.e., value considered as doping
the World Anti-Doping Agency (WADA) Prohibited List,
caffeine can be considered safe, effective, and legal when
used according to established and practiced protocols.
The prevalence of caffeine intake by athletes before
and during competition is high, with the substance obtained
from various sources, such as energy drinks, energy gels,
and tablets, carbonated sodas, and coffee
2
. In previous
studies, caffeine doses commonly range from 3 (low), 6
(moderate)5, and 10 (high)26 mg/kg of body weight when
Acute effects of caffeine intake on athletic performance:
A systematic review and meta-analysis
Efectos agudos de la ingesta de cafeína en el rendimiento
atlético: Una revisión sistemática y meta-análisis
Beatriz Gonçalves Ribeiro1,4, Anderson Pontes Morales1,2,3,4,
Felipe Sampaio-Jorge1,2,3, Felipe de Souza Tinoco1, Alessandra
Alegre de Matos1,3, Tiago Costa Leite1.
1. Laboratory of Research and Innovation in Sports Sciences, Federal
University of Rio de Janeiro UFRJ, Macaé, Brazil
2. Higher Institutes of Education of CENSA, ISECENSA,
Campos dos Goytacazes, Brazil
3. Secretary Municipal of Sport, City, Macaé, Brazil
4. Postgraduate Program in Nutrition, Institute of Nutrition, Federal
University of Rio de Janeiro UFRJ, Rio de Janeiro, Brazil.
Corresponding author. Beatriz Gonçalves Ribeiro. Laboratory of
Research and Innovation in Sports Sciences, Federal University of Rio de
Janeiro - Macaé Campus, RJ, Brazil. 159, Alcides da Conceição, Granja
dos Cavaleiros, Macaé, Rio de Janeiro, Brazil 27930-560.
Telephone: +552227933-378.
E-m ail: ribeirogoncalvesb@gmail.com
Este trabajo fue recibido el 3 de marzo de 2017
ABSTRACT
Objective: Our objective was to perform a systematic re-
view and meta-analysis of the research literature assessing
the effect of caffeine on athletic performance. Methods:
A total of 13 studies published between 2010 and 2015
were included in the meta-analysis of the effects of caffeine
on maximum running distance (2 studies), time trial per-
formance (7 studies), and muscle power (4 studies). The
effect sizes were calculated as standardized differences in
means (std in means). Meta-analysis was completed using
a random effects model. Results: Caffeine supplementation
did not increase maximum running distance (effect size=
0.37, p= 0.14) and muscle power (effect size= 0.17, p=
0.36). However, improvements were observed in the time
trial performance (effect size= -0.40, p< 0.01). Subgroup
analyses revealed that the improvement in time trial results
may be related to the use of the 6 mg/kg of body weight of
caffeine dose (effect size= -0.45, p= 0.01). Conclusion: Our
meta-analysis showed that caffeine intake does not improve
performance in maximum running distance and muscle
power, but it seems to improve time trial performance. The
effect of caffeine on time trial performance related to dose.
Key Words: caffeine, running, exercise test, cycling, muscle
power.
Gonçalves B., et al.
the substance is ingested 30-60 minutes before exercise
to allow the caffeine levels in the bloodstream to reach
peak values.
Caffeine may affect performance through both
peripheral and central mechanisms. The mechanism for
improved endurance, sprint, and power performance has
been related to a simple biologic mechanism, such as
glycogen sparing, increased intracellular Ca
++
concentration,
or altered excitation–contraction coupling
6-9
. However, a
caffeine paradigm for improved athletic performance is a
complex, including biologic mechanisms, and cognitive
perception5. Davis et al.10 proposed a mechanism by which
caffeine delays fatigue through its effects on the central
popularity because of previously known effects of caffeine
Although the physiological basis of caffeine intake
is well described, its clinical effect of improving athletic
performance remains controversial. Caffeine intake has
been reported to be safe to the cardiovascular system that
does not cause changes in heart rate, blood pressure and
heart rate variability11. However, the results are mixed in
the context of “strength”
12
and “resistance” tests
, using
different tests to evaluate the strength (i.e., 1-RM test and
maximal voluntary contraction - MVC) and endurance (i.e.,
repetitions until fatigue). This division does not describe the
tests into only two groups.
A pertinent question is whether the effects of caffeine
supplementation are similar in all tests considered
“endurance” or “strength” and if these effects could be
perspective, this systematic review and meta-analysis of
randomized clinical trials aims to verify whether acute
caffeine supplementation improves athletic performance
regardless of whether the tests involve “endurance” or
“strength”, but considering the same types of tests conducted
by performance athletic.
A systematic review of the literature was carried out
to analyze the acute effects of caffeine intake on athletic
running distance during the test, 2) the time trial performance
in exercise, and 3) the muscle power generated during
exercise. The search included articles published between
January 2010 and December 2015 and was carried out using
the PubMed and Bireme databases. The terms used in the
search were “caffeine” or “exercise” or “performance” or
“drink” or “capsule.” Only studies with humans were included.
Inclusion criteria
with physically active humans (i.e., individuals involved
in physical activities of medium slow/medium-intensity
physical activities); 2) studies with at least two trials (or
separate groups of subjects), in which the subjects consumed
caffeine in one trial (or group) and placebo in the other,
and 3) studies that showed results in absolute values of the
studied variables (i.e., maximum running distance, time trial
performance and muscle power).
with other known or potential ergogenic compounds (i.e.,
creatinine, ginseng, and taurine), used sweetened beverages
containing caffeine or no sugar; 2) trials that included women,
children, adolescents, and sedentary men; 3) studies that
did not have full texts (in such cases, an attempt was made
to retrieve the necessary data by e-mailing the author; and
a full-text analysis of all eligible articles to independently
check if all the inclusion and exclusion criteria were in
agreement. Any disagreement between reviewers was
discussed. If no agreement was reached, a third reviewer
(APM) was consulted.
Data collection
data from all eligible studies. Any disagreement was resolved
as mentioned above. Continuous outcomes, means, and
the data were generally extracted using means, standard
deviations, and sample sizes (n) for both caffeine and
calculated for comparison of continuous outcomes by using
a random effects model.
Assessment of bias risk and study quality
The systematic error of the 13 studies was assessed using
the Cochrane risk of bias tool. The following dimensions
concealment, blinding of participants, blinding of personnel,
blinding of outcome, incomplete outcome data, selective
outcome reporting, and other sources of bias. The risk
about the adequacy of the study and was expressed as “low
risk of bias,” “high risk of bias,” or “unclear risk of bias”15.
Meta-analysis
The meta-analysis was completed using the
Comprehensive Meta-analysis software (version 2.2;
Biostat Inc., Englewood, NJ). The data were extracted
and converted into a standard format by calculating the
size” in the Results and Discussion.
285
Acute effects of caffeine intake on athletic performance: a systematic review and meta-analysis
in the analysis. A total of 13 studies published between
2010 and 2015 were included in the meta-analysis of the
effects of caffeine on maximum running distance (n= 2),
individuals of the studies varied between 20.8 and 36.2
years. One study, however, did not report the age of the
subjects. The dosage of caffeine varied between ~2.5 and
the whole sample. In this case, to categorize the amount of
caffeine consumed, the quantity of consumed caffeine was
divided by the mean body mass of the sample. All articles
used caffeine in capsules. General characteristic of the
studies included on systematic review and meta-analysis
are shown in Table 1.
Analysis of the subgroup of quantitative data (Dosage)
Table 2 illustrates the effect sizes of trials related to
dosage (maximum running distance, time trial performance
and muscle power). The dosage of 6 mg/kg on the time
trial performance was significant with the effect size of
were identified for the effects for <6 mg/kg dosage in
the time trial performance (p= 0.18). Comparisons with
maximum running distance and muscle power were not
possible, since few articles were included for analysis
in subgroup.
Assessment of quality and publication bias
Two of the studies assessed had a clear description of
the random sequence generation (low risk of bias). Only one
study reported allocation concealment (low risk of bias). A
complete description of blinding of participants (low risk of
bias) was observed in 11 studies, and blinding of personnel
(low risk of bias) in 8 studies. One article had complete
information on blinding of outcome assessors (low risk of
bias); one article had incomplete outcomes (high risk of
bias). All 13 evaluated studies reported selective outcomes
Figure 1.
286
Gonçalves B., et al.
Table 1
General characteristic of the studies included in the systematic review and meta-analysis.
Time of
Form of Caffeine consumption Measurement Measurement Mean ± SD Mean ± SD
Reference ingestion Subjects info dosage pre-exercise (min) Test Unit Caffeine Placebo
10 male cyclists; Time Tria l
2652 ± 270
178 ± 6 cm;
73 ± 6 kg
Maximum
Distance
13 male cyclists; Time Trial
176 ± 6 cm;
71 ± 9 kg
16 male cyclists; Time Trial
180.9 + 5.5 cm;
78.5 ± 6.0 kg
17 well-trained 10 Muscle
182 ± 0.06 cm;
82.2 ± 6.9 kg
12 male cyclists; Time Trial
80.2 ± 6.6 kg
12 male; Maximum
183 ± 7 cm; Distance
10 male cyclists; Muscle
177.5 ± 6.09 cm;
78.1±13.9 kg
12 male judoists; Muscle
1.76 ± 6.57 cm;
83.75 ± 20.2 kg
13 active males; Muscle
177 ± 0.06 cm;
77. 1± 7.2 k g
10 male cyclists; Time Trial
79.10 ± 1.65 kg
16 male cyclists; Time Trial
178.2 ± 8.8 cm;
287
Acute effects of caffeine intake on athletic performance: a systematic review and meta-analysis
Table 2
time trial performance and muscle power using a random effect model.
Time Trial
Maximum Running Distance Performance Muscle Power
Effect size Effect size
n (95% CL) p n Effect size (95% CL) p n (95% CL) p
Dosage
> 6 mg/kg - - - - - - 1 - -
< 6 mg/kg 1 - - 3 -0.32 (-0.80 to 0.15) 0.18 2 0.26 (-0.29 to 0.81) 0.35
Figure 2.
288
Gonçalves B., et al.
Effect of caffeine intake on maximum running distance
designed to estimate the maximum oxygen uptake - VO2max
and the maximum running distance by athletes) to assess the
maximum running distance of the subjects. The authors used
caffeine dosage of 5 mg/kg of body weight16 and 6 mg/kg of
body weight17 and found no improvement in the maximum
heterogeneity between the studies (I2= 0.00; p= 0.55).
Effect of caffeine intake on time trial performance
caffeine dosage of 6 mg/kg of body weight5,18 -20 , two studies
used a caffeine dosage of 3 mg/kg of body weight and
(~2.5 mg/kg of body weight)22. Desbrow et al.18 and Irwin
et al. evaluated the shortest time to reach a target amount
of work among cyclists. Bortolotti et al.5 and Acker-Hewitt
et al.
21
al.2220 and Womack et al.19 used a distance
performance among the subjects who ingested caffeine
the studies (I2= 0.00; p= 0.87).
Effect of caffeine intake on muscle power
cycling. Three of these studies23-25 used the Wingate test;
the other study26 used seven sprints for a maximum of 10
seconds. The average dosage of caffeine was 6.5 mg/kg of
body weight. The studies did not show an improvement in
the muscle power generated by the subjects who ingested
Figure 3.
Figure 4.
289
Acute effects of caffeine intake on athletic performance: a systematic review and meta-analysis
The aims of this systematic review and meta-analysis
were to evaluate the effects of caffeine supplementation
was that caffeine improves performance on the time trials
performance, but not on maximum running distance and
muscle power test. In addition, subgroup analysis revealed
that the effect of caffeine in the time trials performance test
may be related to 6 mg/kg of body weight dosage.
The exact mechanisms by which caffeine exerts ergogenic
effects are still under debate, with suggested mechanisms
including fatty acid mobilization and oxidation and endogenous
glycogen content sparing, attenuating fatigue27. The studies
included in the evaluation of the maximum running distance
did not improved performance with the use of caffeine (p=
response of caffeine. According to the hypothesis of Bassini
et al.
16
, the hyperammonic state changes the function of the
blood-brain barrier and is postulated to cause central fatigue
during exercise. However, we observed that the maximum
running distance was small to induce hyperammonemia in
athletes and consequently it was also small to test the positive
ergogenic effect of caffeine. Marriot et al.17 reported high
variation in maximum running distance between assessed
subjects, which they attributed to the existence of “high”
and “low” responders to caffeine.
time trial results may be related to the dose. According to
Desbrow et al.
18
, the use of high caffeine dosage could
increase blood concentration of epinephrine and improve
performance during the time trials performance test.
20 explained that independent of dosage, for
occur, greater availability of muscle is required (i.e., increased
concentrations of caffeine at the site of action). Additionally,
Irwin et al. showed that acute caffeine supplementation
positively affected exercise performance. The positive
ergogenic effect of caffeine was found to be related to
alteration in the rating of perceived exertion. Desbrow et
al.18 suggested that this mechanism (i.e., the central effects
mediated by adenosine receptor antagonism) might explain
the ergogenic effect of caffeine on exercise performance
by using the time trials performance.
et al.
21
and Bortolotti et al.
5
may relate to the nature of the
performance protocol. Bortolotti et al.5 used closed-loop
protocol time trials. This allowed for the development of
time, preventing the athlete from reaching exhaustion.
On the other hand, although different doses of caffeine
were used, there were similarities in the methodologies
applied by Bortolotti et al.
5
, Acker-Hewitt et al.
21
, and
22
. In these three studies, participants ingested
caffeine 60 minutes before the test and were instructed not
hours before testing.
Regular consumption of caffeine has been associated
with an upregulation of the number of adenosine receptors
in the vascular and neural tissues of the brain
28,29
. Based on
these observations, it could be speculated that habitual and
non-habitual caffeine consumers would respond differently
to caffeine supplementation during exercise. The minimum
period of caffeine fasting in diet that is needed to obtain
greater sensitivity to its action is not well established in
30 indicated that the time
required for the beginning of abstinence varies between
in the current study, it is possible that the subjects had low
sensitivity to caffeine, which would require a longer period
of abstinence and/or an increase in the dosage used. In
22, subjects were consumers of
caffeine; thus, the dosage of 2.5 mg/kg of body weight used
may be considered low. In fact, Warren et al.31 indicated in
their meta-analysis that the commonly used caffeine dosage
These results reinforce the notion that responses to
caffeine may be triggered by other factors, such as genetics,
Figure 5.
290
Gonçalves B., et al.
rather than habitual caffeine intake per se. According to
Womack et al.19, genetic polymorphisms in genes related
to caffeine metabolism (aryl-hydrocarbon receptor [AHR],
(Decaprenyl)) are a potential explanation for the variability
in the ergogenic response to caffeine supplementation in
effect of supplementation with 6 mg/kg of body weight of
anhydrous caffeine on the performance of cyclists. Given
metabolism would be advantageous for maximizing the
performance of cyclists homozygous for the AA (i.e., caffeine
is metabolized at a higher rate) variant to a greater degree
compared with cyclists with the C (i.e., caffeine is metabolized
homozygotes compared with 1.3 minutes in the C-allele
carriers. The authors speculate that the rapid accumulation
of caffeine metabolites may have been responsible for the
positive ergogenic effect in AA homozygotes. Paraxanthin
and theophylline (metabolites downstream of caffeine
receptors than caffeine32. Thus, it is possible that a faster
caffeine metabolism in AA homozygotes created a faster
production of paraxanthine and/or theophylline and thus
increases the ergogenic effect.
It has been suggested that caffeine increases strength
and muscle power performance through greater motor unit
reticulum, and surges in nitric oxide concentrations, working
collectively to produce stronger muscle contractions
33
. H owever,
, which could help to explain
the limited ergogenic effect upon maximal strength and
muscle power. In their evaluation of the contractile properties
25
al.23 and Glaister et al.26
caffeine use in cyclists may be more effective in longer time
evaluations of muscle power compared to shorter tests. Thus
further research is needed to elucidate the ergogenic effects
of caffeine during muscle strength exercises.
In conclusion, this meta-analysis showed that caffeine
intake does not improve performance in maximum running
distance and muscle power, but seems to improve time
trial performance. The potential effect of caffeine on time
trial performance related to caffeine dose. The results
of the present study contribute to the knowledge of the
ergogenic effects of caffeine in several tests that evaluate
athletic performance.
the design, analysis or writing of this article.
B.G.R and A.A.M (Nutritionist) designed the database,
carried out the majority of the meta-analysis and contributed
to the writing and the critical review of the manuscript;
search and database storage and helped to design and
provided guidance for the meta-analyses used;
part of the literature search, and extraction and contributed
to the writing of the manuscript;
literature review and the discussion of manuscript;
T.C.L (Nutritionist) helped with the literature review and
provided a critical revision of the manuscript, especially the
discussion of results.
de la literatura de investigación que evalúa el efecto de la
estudios publicados entre 2010 y 2015 fueron incluidos en el
del efecto se calcularon como diferencias estandarizadas
completó utilizando un modelo de efectos aleatorios.
la mejora en los resultados de los ensayos a tiempo podía
estar relacionada con el uso de la dosis de 6 mg/kg de peso
de carrera ni la potencia muscular, pero parece mejorar el
rendimiento de la prueba de tiempo. Este efecto potencial
de la cafeína en el rendimiento de la prueba de tiempo
estuvo relacionado con la dosis.
ejercicio, ciclo, energía del músculo.
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