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Objective: Our objective was to perform a systematic review 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 performance (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.
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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.2220 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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... In addition, 89% of athletes competing at the 2005 Ironman™ triathlon world championships revealed that they were planning on using a caffeine substance before and/or during the event [4]. This is not surprising, as preexercise caffeine intake of 2-6 mg/kg body mass has generally been shown to confer a worthwhile improvement in endurance performance (EP) under thermoneutral conditions [2,[5][6][7][8][9]. It is proposed that caffeine may contribute to enhance exercise performance by increasing motivation [10] and alertness [11], reducing perceived exertion [12][13][14] and fatigue [14,15], enhancing the mobilization of intracellular calcium and free fatty acids [16], and most importantly by acting as an adenosine receptor antagonist [17]. ...
... The search strategy used for study selection is presented in Fig. 1. An initial search was performed using crossreferencing of the reference sections of five meta-analyses [2,5,7,44,45] retrieved in an umbrella meta-analysis [8] and two narrative reviews [9,46]. Then, a traditional literature search, limited to original peer-reviewed articles published in French or English, was performed on MEDLINE, SPORTDiscus, AMED and CINAHL databases, combining a "title field" and an "abstract field" research using the following keywords alone or in combination with truncation: caffein*, dehydrat*, endurance, exercise, heat, hot, humid*, temper*, therm*, performance. ...
... While several systematic reviews, including meta-analyses [2,5,7,44,45] and an umbrella review [8], have reported on the impact of pre-exercise caffeine ingestion on EP, specific investigations of its impact in warm or hot environments are limited. Therefore, the goal of the current work was to extend that of the previous meta-analyses by exclusively focusing on the impact of pre-exercise caffeine ingestion on EP and C T during exercise undertaken in the heat. ...
Article
Full-text available
Background Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat. Objective To use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat. Design Systematic review with meta-analysis. Data Sources Four databases and cross-referencing. Data Analysis Weighted mean effect summaries using robust variance random-effects models for EP and CT, as well as robust variance meta-regressions to explore confounders. Study Selection Placebo-controlled, randomized studies in adults (≥ 18 years old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27 °C. Results Respectively six and 12 studies examined caffeine’s impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of ~ 70 min conducted at 34 °C and 47% relative humidity. Caffeine supplementation non-significantly improved EP by 2.1 ± 0.8% (95% CI − 0.7 to 4.8) and significantly increased the rate of change in CT by 0.10 ± 0.03 °C/h (95% CI 0.02 to 0.19), compared with the ingestion of a placebo. Conclusion Caffeine ingestion of 6 mg/kg body mass ~ 1 h before exercise in the heat may provide a worthwhile improvement in EP, is unlikely to be deleterious to EP, and trivially increases the rate of change in CT.
... The search for licit ergogenic resources is growing by cyclists in an attempt to minimize muscle fatigue generated in training sessions/competitions. In cyclists, muscle fatigue is manifested by the inability to repeatedly produce muscle strength or power over some time [1]. The ergogenic aid can be characterized as a supplement that delays fatigue, thus maintaining the output power and contributing to the improvement of sports performance [1,2]. ...
... In cyclists, muscle fatigue is manifested by the inability to repeatedly produce muscle strength or power over some time [1]. The ergogenic aid can be characterized as a supplement that delays fatigue, thus maintaining the output power and contributing to the improvement of sports performance [1,2]. In this scenario, caffeine (1, 3, 7-trimethylxanthine) has been described as a licit ergogenic resource that is effective in increasing performance in various sports (i.e., triathlon, and cycling) [1,3], in particular, sports that mainly involve muscle strength/power and aerobic endurance [1,2]. ...
... The ergogenic aid can be characterized as a supplement that delays fatigue, thus maintaining the output power and contributing to the improvement of sports performance [1,2]. In this scenario, caffeine (1, 3, 7-trimethylxanthine) has been described as a licit ergogenic resource that is effective in increasing performance in various sports (i.e., triathlon, and cycling) [1,3], in particular, sports that mainly involve muscle strength/power and aerobic endurance [1,2]. ...
Article
Full-text available
The present study investigated whether the caffeine supplementation for four days would induce tolerance to the ergogenic effects promoted by acute intake on physiological, metabolic, and performance parameters of cyclists. A double-blind placebo-controlled cross-over design was employed, involving four experimental trials; placebo (4-day)-placebo (acute)/PP, placebo (4-day)-caffeine (acute)/PC, caffeine (4-day)-caffeine (acute)/CC and caffeine (4-day)-placebo (acute)/CP. Fourteen male recreationally-trained cyclists ingested capsules containing either placebo or caffeine (6 mg·kg −1) for 4 days. On day 5 (acute), capsules containing placebo or caffeine (6 mg·kg −1) were ingested 60 min before completing a 16 km time-trial (TT). CC and PC showed improvements in time (3.54%, ES = 0.72; 2.53%, ES = 0.51) and in output power (2.85%, ES = 0.25; 2.53%, ES = 0.20) (p < 0.05) compared to CP and PP conditions, respectively. These effects were accompanied by increased heart rate (2.63%, ES = 0.47; 1.99%, ES = 0.34), minute volume (13.11%, ES = 0.61; 16.32%, ES = 0.75), expired O 2 fraction (3.29%, ES = 0.96; 2.87, ES = 0.72), lactate blood concentration (immediately after, 29.51% ES = 0.78; 28.21% ES = 0.73 recovery (10 min), 36.01% ES = 0.84; 31.22% ES = 0.81), and reduction in expired CO 2 fraction (7.64%, ES = 0.64; 7.75%, ES = 0.56). In conclusion, these results indicate that caffeine, when ingested by cyclists in a dose of 6 mg·kg −1 for 4 days, does not induce tolerance to the ergogenic effects promoted by acute intake on physiological, metabolic, and performance parameters.
... Ergogenic aids are substances, techniques, or sports equipment that enhance performance. Caffeine is an ergogenic aid [5] and the principal ingredient of EDs. They are promoted as a factor that increases energy, alertness, and athletic performance [1,6]; therefore, it seems like a good choice for athletes. ...
... Modern meta-analysis has revealed that caffeine intake does not improve performance in maximum running distance and muscle power, but it seems to improve time trial performance. The result is doserelated [5,29]. It is also unclear whether EDs are the vehicle for caffeine delivery when large doses are required [19]. ...
Article
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The energy drinks are beverages that contain caffeine and are consumed by students, children, adolescents and young adults to enhance their athletic and cognitive performance. Significant adverse effects have been reported. They vary from mild symptoms to death. The present study attempts to assess the risk of using energy drinks by exercisers and athletes. In order to achieve this, we evaluate the consumption and knowledge level of the consumers. The lack of awareness can lead to dangerous practices. Views on appropriate public health protection measures are also being investigated. The grade of consumption (35.5%) is within the bounds of the literature. The main source of knowledge is the advertisement (69.2%), which does not guarantee objective information. Therefore, although exercisers and athletes believe that they have adequate knowledge on the subject (91.2%), in fact this is not the case (the knowledge score is 10.12/18). Thus, half of them consume concurrently energy drinks with alcohol (a perilous practice). The study emphasizes the need of taking measures for public health protection.
... One meta-analysis reported that caffeine ingestion enhances mean and peak power during the Wingate test [230], although the effect sizes of 0.18 (+ 3%) and 0.27 (+ 4%), respectively are modest. In contrast, another meta-analysis that examined the effects of caffeine on muscle power as assessed with the Wingate test for three of the studies, and repeated sprints for a maximum of 10-s for the fourth, did not report benefits from ingestion of caffeine [231]. An average caffeine dose of 6.5 mg/kg of body mass was used across the four studies with no improvements in muscle power under caffeine conditions (effect size = 0.17, p = 0.36) compared to placebo trials, although the data collected spanned only 5 years [231]. ...
... In contrast, another meta-analysis that examined the effects of caffeine on muscle power as assessed with the Wingate test for three of the studies, and repeated sprints for a maximum of 10-s for the fourth, did not report benefits from ingestion of caffeine [231]. An average caffeine dose of 6.5 mg/kg of body mass was used across the four studies with no improvements in muscle power under caffeine conditions (effect size = 0.17, p = 0.36) compared to placebo trials, although the data collected spanned only 5 years [231]. A study by Lee et al. [232] reported that caffeine ingestion enhanced sprint performance involving a 90-s rest interval (i.e., intermittent-sprinting) but did not benefit repeated-sprints with a 20-s rest interval. ...
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Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3–6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4–6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.
... To date, a wide range of acute and chronic interventions have been investigated regarding performance improvement in endurance exercises [3,4]. Caffeine (1,3,7trimethylxanthine) has been described as an effective ergogenic aid for enhancing performance in various sports [5][6][7][8][9][10]. Many researchers [11,12] have argued that the primary focus behind the ventilatory effect (i.e., increased alveolar ventilation) of caffeine is the central stimulation of the respiratory medullary complex. ...
... Although our findings indicate that the acute use of caffeine (PC) improved the performance (Figure 3 These results should be interpreted with caution considering inter-individual variability observed in the metabolism of caffeine. According to Ribeiro et al. [8], genetic polymorphisms in related genes to caffeine metabolism (aryl-hydrocarbon receptor [AHR], cytochrome P450 1A1 and 1A2 (CYP1A1-CYP1A2, Prenyl (Decaprenyl)) are a potential explanation for the variability in the ergogenic response to caffeine supplementation in trained athletes. Given these prior findings, it could be hypothesized that a slower metabolism would be advantageous for maximizing the ergogenic benefit of caffeine [28]. ...
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Introduction: The aim of this study was to test the hypothesis that caffeine supplementation (6 mg·kg-1 body mass) for 4-days, followed by acute intake, would impact five male triathletes output power after performed submaximal intensity exercise. Methods: This was a randomized, double-blind, placebo-controlled crossover study, placebo (4-days)-placebo (acute) PP, placebo (4-days)-caffeine (acute) PC, and caffeine (4-days)-caffeine (acute) CC. Participants abstained from dietary caffeine sources for 4 days and ingested capsules containing either placebo or caffeine (6 mg.kg-1 body mass day in one absorption). The acute trials the capsules containing placebo or caffeine (6 mg. kg-1 body mass day in one absorption) were ingested 60min before completing exercise in a treadmill for 40min (80% VO2max) and to perform the Wingate test. Results: Blood lactate was determined before, 60min after ingestion, and immediately after the exercise on the treadmill, the Wingate test, and after the recovery (10-min). CC and PC trials did not change the cardiopulmonary variables (P>0.05) and the anaerobic power variables (peak/mean power output and fatigue index) (P>0.05). The PC trial compared with PP promoted improvements in the curve power output in 2 sec by 31.19% (large effect-size d = 1.08; P<0.05) and 3 sec by 20% (large effect-size d = 1.19; P<0.05). A 10min recovery was not sufficient to reduce blood lactate concentration in the PC trial compared with PP (PC, 13.73±2.66 vs. PP, 10.26±1.60 mmol.L-1 ; P<0.05, respectively) (P<0.05). Conclusion: In conclusion, these results indicate that caffeine supplementation (6 mg·kg-1 body mass) for 4 days, followed by acute ingestion, did not impact the triathletes output power after performed submaximal intensity exercise. Nutritional interventions may help researchers and athletes to adapt strategies for manipulating caffeine use.
... Numerous meta-analyses have demonstrated small but significant improvements in endurance [4,5], muscular function [5][6][7] and sportspecific skills [8,9] following acute caffeine ingestion. As such, caffeine has become a popular nutritional supplement to improve sports performance [9][10][11]. ...
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This study aimed to determine the effect of 3 mg.kg−1 acute caffeine ingestion on muscular strength, power and strength endurance and the repeatability of potential ergogenic effects across multiple trials. Twenty-two university standard male rugby union players (20 ± 2 years) completed the study. Using a double-blind, randomized, and counterbalanced within-subject experimental design. Participants completed six experimental trials (three caffeine and three placebo) where force time characteristic of the Isometric Mid-Thigh Pull (IMTP), Countermovement Jump (CMJ) and Drop Jumps (DJ) were assessed followed by assessments of Chest Press (CP), Shoulder Press (SP), Squats (SQ), and Deadlifts (DL) Repetitions Until Failure (RTF at 70% 1 RM). ANOVA indicated that caffeine improved both the CMJ and DJ (p < 0.044) and increased RTF in all RTF assessments (p < 0.002). When individual caffeine trials were compared to corresponding placebo trials, effect sizes ranged from trivial-large favoring caffeine irrespective of a main effect of treatment being identified in the ANOVA. These results demonstrate for the first time that the performance enhancing effects of caffeine may not be repeatable between days, where our data uniquely indicates that this is in part attributable to between sessions variation in caffeine’s ergogenic potential.
... To address the apparent discrepancies between individual studies two previous meta-analyses explored the effects of caffeine on performance in the Yo-Yo test. In the first analysis, Gonçalves Ribeiro et al. 10 reported no significant effects of caffeine on performance in this test. However, the analysis included only two studies with a combined number of participants amounting to 31. ...
Article
OBJECTIVES: To conduct a systematic review and a meta-analysis of studies exploring the effects of caffeine and/or sodium bicarbonate on performance in the Yo-Yo test. DESIGN: Systematic review/meta-analysis. METHODS: A total of six databases were searched, and random-effects meta-analyses were performed examining the isolated effects of caffeine and sodium bicarbonate on performance in the Yo-Yo test. RESULTS: After reviewing 988 search records, 15 studies were included. For the effects of caffeine on performance in the Yo-Yo test, the meta-analysis indicated a significant favoring of caffeine as compared with the placebo conditions (p = 0.022; standardized mean difference [SMD] = 0.17; 95% CI: 0.08, 0.32; +7.5%). Subgroup analyses indicated that the effects of caffeine were significant for the level 2 version of the Yo-Yo test, but not level 1. Four out of the five studies that explored the effects of sodium bicarbonate used the level 2 version of the Yo-Yo test. The pooled SMD favored the sodium bicarbonate condition as compared with the placebo/control conditions (p = 0.007; SMD: 0.36; 95% CI: 0.10, 0.63; +16.0%). CONCLUSIONS: This review demonstrates that isolated ingestion of caffeine and sodium bicarbonate enhances performance in the Yo-Yo test. Given these ergogenic effects, the intake of caffeine and sodium bicarbonate before the Yo-Yo test needs to be standardized (i.e., either restricted or used in the same way before each testing session). Furthermore, the results suggest that individuals competing in sports involving intermittent exercise may consider supplementing with caffeine or sodium bicarbonate for acute improvements in performance.
... These metabolic alterations induced by caffeine suggest that caffeine accelerates contraction-induced metabolic activations, thereby contributing to muscle endurance performance and exercise benefits to our health. effects on muscle power output and endurance performance [13][14][15]. These findings suggest that caffeine accelerates muscle contraction-induced metabolic activation, thereby contributing to exercise benefits toward health promotion. ...
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Exercise has beneficial effects on our health by stimulating metabolic activation of skeletal muscle contraction. Caffeine is a powerful metabolic stimulant in the skeletal muscle that has ergogenic effects, including enhanced muscle power output and endurance capacity. In the present study, we aim to characterize the metabolic signatures of contracting muscles with or without caffeine stimulation using liquid chromatography-mass spectrometry and capillary electrophoresis coupled to mass spectrometry. Isolated rat epitrochlearis muscle was incubated in the presence or absence or of 3 mM caffeine for 30 min. Electrical stimulation (ES) was used to induce tetanic contractions during the final 10 min of incubation. Principal component analysis and hierarchical clustering analysis detected 184 distinct metabolites across three experimental groups—basal, ES, and ES with caffeine (ES + C). Significance Analysis of Microarray identified a total of 50 metabolites with significant changes in expression, and 23 metabolites significantly changed between the ES and ES + C groups. Changes were observed in metabolite levels of various metabolic pathways, including the pentose phosphate, nucleotide synthesis, β-oxidation, tricarboxylic acid cycle, and amino acid metabolism. In particular, D-ribose 5-phosphate, IMP, O-acetylcarnitine, butyrylcarnitine, L-leucine, L-valine, and L-aspartate levels were higher in the ES + C group than in the ES group. These metabolic alterations induced by caffeine suggest that caffeine accelerates contraction-induced metabolic activations, thereby contributing to muscle endurance performance and exercise benefits to our health.
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Amaç: Bu araştırmada Kafein kullanımımın performansı arttırdığı çalışmalarda gösterilmiştir ancak kullanılan kafein kahve şeklindedir. Bu bağlamda bu çalışmanın amacı elit futbolcularda kafein kullanımının çeviklik ve dayanıklılık performansına olan etkisinin değerlendirilmesidir. Gereç ve Yöntem: Bu araştırmada Aydın Yıldızspor Futbol Kulübünün 10 kişiden oluşan lisanslı sporcu grubuna, Kafeinin akut etkisini ölçmek amaçlı 9 haftalık bir test uygulanmıştır. Sporculara hiçbir içecek tüketmeden, kafeinli kahve ve kafeinsiz kahve tükettikten sonraki çeviklik (T-test) ve dayanıklılık performansları (Yo-Yo Aralıklı Toparlanma Testi) ölçülmüştür. Bulgular: Çalışma sonuçlarına göre direkt, kafeinli ve kafeinsiz çeviklik ölçümleri sonucunda küresellik varsayımı yoktur (p>0,05) ve istatiksel açıdan 3 farklı ölçüm arasında istatiksel açıdan anlamlı farklılık çıkmıştır (p0,05) ve istatiksel açıdan 3 farklı ölçüm arasında istatiksel açıdan anlamlı farklılık çıkmıştır (p
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CrossFit (CF) is characterized as a constantly varied high-intensity functional movement training program, performed with little or no rest between bouts, combining strength and endurance exercises, such as running, cycling, rowing, Olympic weightlifting, power weightlifting, and gymnastic-type exercises. Several nutritional strategies are used to improve sports performance of CF practitioners; however, most of them are empirical and lack scientific evidence. Thus, the aim of this review was to determine the effect of diet intervention, dietary supplements, and performance-enhancing substances in exercise-performance parameters of CF practitioners. MEDLINE/PubMed, Web of Science, LILACS, SciELO, and Scopus databases were searched using specific Medical Subject Headings and keywords for clinical studies which enrolled CF athletes in a diet, dietary supplements, or performance-enhancing substances intervention. Athletic performance was considered as the primary outcome. No other filters were applied. Including grey literature search, a total of 217 studies and 2 abstracts were identified, however only 14 studies met the eligibility criteria. Two studies evaluated the effect of caffeine supplementation on exercise performance and performance parameters; five studies evaluated high or low carbohydrate effect on performance and other parameters. One study verified the effect of multi-ingredient supplementation on CF-specific performance and body composition. One study compared protein supplements intake on performance and body composition. Two studies assessed the effect of green tea and (-)-epicatechin on performance and other parameters. One study evaluated the effects of nitrate supplementation on exercise performance. One study investigated the effect of betaine supplementation on body composition and muscle performance. Finally, one study examined the effects of sodium bicarbonate (SB) ingestion on exercise performance and aerobic capacity. Only sodium bicarbonate (SB) supplementation improved CF performance. These outcomes may have been obtained due to methodological limitations such as small sample size, lack of control over influencing variables, short period of exercise intervention. Despite the popularity and growing evidence about the CF, little is known about the relationship between performance-enhancing substances or dietary interventions and CF performance. Given the lack of scientific evidence, new studies with potential ergogenic supplements, good methodological model, and practical application are required.
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Caffeine and sodium bicarbonate ingestion have been suggested to improve high-intensity intermittent exercise, but it is unclear if these ergogenic substances affect performance under provoked metabolic acidification. To study the effects of caffeine and sodium bicarbonate on intense intermittent exercise performance and metabolic markers under exercise-induced acidification, intense arm-cranking exercise was performed prior to intense intermittent running after intake of placebo, caffeine and sodium bicarbonate. Male team-sports athletes (n = 12) ingested sodium bicarbonate (NaHCO3; 0.4 g.kg(-1) b.w.), caffeine (CAF; 6 mg.kg(-1) b.w.) or placebo (PLA) on three different occasions. Thereafter, participants engaged in intense arm exercise prior to the Yo-Yo intermittent recovery test level-2 (Yo-Yo IR2). Heart rate, blood lactate and glucose as well as rating of perceived exertion (RPE) were determined during the protocol. CAF and NaHCO3 elicited a 14 and 23% improvement (P < 0.05), respectively, in Yo-Yo IR2 performance, post arm exercise compared to PLA. The NaHCO3 trial displayed higher [blood lactate] (P < 0.05) compared to CAF and PLA (10.5 ± 1.9 vs. 8.8 ± 1.7 and 7.7 ± 2.0 mmol.L(-1), respectively) after the Yo-Yo IR2. At exhaustion CAF demonstrated higher (P < 0.05) [blood glucose] compared to PLA and NaHCO3 (5.5 ± 0.7 vs. 4.2 ± 0.9 vs. 4.1 ± 0.9 mmol.L(-1), respectively). RPE was lower (P < 0.05) during the Yo-Yo IR2 test in the NaHCO3 trial in comparison to CAF and PLA, while no difference in heart rate was observed between trials. Caffeine and sodium bicarbonate administration improved Yo-Yo IR2 performance and lowered perceived exertion after intense arm cranking exercise, with greater overall effects of sodium bicarbonate intake.
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The aim was to investigate the effect of caffeine on anaerobic power intermittently trained cyclists. Ten athletes underwent two experimental sessions in a model randomized double-blind study. In each session, subjects ingested a random capsule caffeine (6 mg / kg) or placebo. One hour after, two tests Wingate were carried (T1, T2) for determining the anaerobic performance with 4 min of rest between each exercise bout. Statistical analysis used ANOVA for repeated measures revealed no significant differences between the caffeine and placebo trials. In comparing intra-tests was significantly reduced only to Mean Power (W) between sessions with caffeine (T1c: 673.6 ± 59.5 vs. T2c: 589.0 ± 58.8). The acute oral intake of caffeine did not contribute to the increase in intermittent anaerobic performance, however, the reduction in average power with the use of caffeine, may suggest a preference for fatty acid metabolism, which would be disadvantageous during intermittent maximal efforts.
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The purpose of this research was to investigate the effects of exercise capacity, heart rate recovery and heart rate variability after high-intensity exercise on caffeine concentration of energy drink. The volunteers for this study were 15 male university student. 15 subjects were taken basic physical examinations such as height, weight and BMI before the experiment. Primary tests were examined of VO2max per weight of each subjects by graded exercise test using Bruce protocol. Each of five subject was divided 3 groups (CON, ECGⅠ, ECGⅡ) by matched method based on weight and VO2max per weight what gained of primary test for minimize the differences of exercise capacity and ingestion of each groups. For the secondary tests, the groups of subjects were taken their materials before and after exercise as a blind test. After the ingestion, subjects were experimented on exercise test of VO2max 80% by treadmill until the all-out. Heart rate was measured by 1minute interval, and respiratory variables were analyzed VO2, VE, VT, RR and so on by automatic respiratory analyzer. And exercise exhaustion time was determined by stopwatch. Moreover, HRV was measured after exercise and recovery 3 min. Among the intake groups, ECGⅡ was showed the longest of exercise exhaustion time more than CON group (p = .05). Result of heart rate during exercise according to intake groups, there was significant differences of each time (p < .001), however, not significant differences of each groups and group verse time (p > .05). Result of RPE during exercise according to intake groups, there was significant differences of each time (p < .001), however, not significant differences of each groups and group verse time (p > .05). In conclusion, EDGⅡ showed the significant increase of exercise exhaustion time more than CON group (p=.05) and not significant differences in HR, RPE, RER, HRV, HRR, blood pressure (p > .05). Therefore, 2.5 mg/kg(-1) ingestion of energy drink might be positive effect to increase exercise performance capacity without side-effect in cardiovascular disease.
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Both caffeine (CAF) and pseudoephedrine (PSE) are proposed to be central nervous system stimulants. However, during competition, CAF is a permitted substance, whereas PSE is a banned substance at urinary levels >150 μg.L-1. As a result, this study aimed to compare the effect of CAF versus PSE use on cycling time trial (TT) performance to explore whether the legal stimulant was any less ergogenic that the banned substance. Here, 10 well-trained male cyclists and/or triathletes were recruited for participation. All athletes were required to attend the laboratory on four separate occasions, inclusive of a familiarisation trial and three experimental trials which required participants to complete a simulated 40 km (1200 kJ) cycling TT, after the ingestion of either 200 mg CAF, 180 mg PSE or a non-nutritive placebo (PLA). The results showed that the total time taken and the mean power produced during each TT was not significantly different (p>0.05) between trials, despite a 1.3% faster overall time (~57 sec) after CAF consumption. Interestingly, the time taken to complete the second 50% of the TT was significantly faster (p<0.05) in CAF as compared to PSE (by 99 sec), with magnitude based inferences suggesting a 91% beneficial effect of CAF during the second half of the TT. This investigation further confirms the ergogenic benefits of CAF use during TT performances, and further suggests this legal CNS stimulant has a better influence than a supra-therapeutic dose of PSE.
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The purpose of the present study was to evaluate the ergogenic effect of caffeine ingestion on mood state, simple reaction time, and muscle power during the Wingate test recorded in the morning on elite Judoists. TWELVE ELITE JUDOISTS (AGE: 21.08 ± 1.16 years, body mass: 83.75 ± 20.2 kg, height: 1.76 ±6.57 m) participated in this study. Mood states, simple reaction time, and muscle power during the Wingate test were measured during two test sessions at 07:00 h and after placebo or caffeine ingestion (i.e. 5 mg/kg). Plasma concentrations of caffeine were measured before (T0) and 1-h after caffeine' ingestion (T1) and after the Wingate test (T3). Our results revealed an increase of the anxiety and the vigor (P<0.01), a reduction of the simple reaction time (P<0.001) and an improvement of the peak and mean powers during the Wingate test. However, the fatigue index during this test was unaffected by the caffeine ingestion. In addition, plasma concentration of caffeine was significantly higher at T1 in comparison with T0. In conclusion, the results of this study suggest that morning caffeine ingestion has ergogenic properties with the potential to benefit performance, increase anxiety and vigor, and decrease the simple reaction time.
Article
Purpose: We investigated the effects of caffeine on the ammonia and amino acid metabolism of elite soccer players. Methods: In this double-blind randomized study, athletes (n = 19) received 5 mg·kg caffeine or lactose (LEx, control) and performed 45 min of intermittent exercise followed by an intermittent recovery test (Yo-Yo IR2) until exhaustion. The caffeine-supplemented athletes were divided into two groups (CEx and SCEx) depending on their serum caffeine levels (<900% and >10,000%, respectively). Data were analyzed by ANOVA and Tukey post hoc test (P < 0.05 was considered to be statistically significant). Results: Caffeine supplementation did not significantly affect the performance (LEx = 12.3 ± 0.3 km·h, 1449 ± 378 m; CEx = 12.2 ± 0.5 km·h, 1540 ± 630 m; SCEx = 12.3 ± 0.5 km·h, 1367 ± 330 m). Exercise changed the blood concentrations of several amino acids and increased the serum concentrations of ammonia, glucose, lactate, and insulin. The LEx group showed an exercise-induced increase in valine (∼29%), which was inhibited by caffeine. Higher serum caffeine levels abolished the exercise-induced increase (∼24%-27%) in glutamine but did not affect the exercise-induced increase in alanine (∼110%-160%) and glutamate (42%-61%). In response to exercise, the SCEx subjects did not exhibit an increase in uremia and showed a significantly lower increase in their serum arginine (15%), citrulline (16%), and ornithine (ND) concentrations. Conclusions: Our data suggest that caffeine might decrease systemic urea by decreasing the glutamine serum concentration, which decreases the transportation of ammonia to the liver and thus urea synthesis.
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Background The objective of this study was to analyze the effect of caffeine ingestion on the performance and physiological variables associated with fatigue in 20-km cycling time trials. Methods In a double-blind placebo-controlled crossover study, 13 male cyclists (26 ± 10 y, 71 ± 9 kg, 176 ± 6 cm) were randomized into 2 groups and received caffeine (CAF) capsules (6 mg.kg−1) or placebo (PLA) 60 min before performing 20-km time trials. Distance, speed, power, rpm, rating of perceived exertion (RPE), electromyography (EMG) of the quadriceps muscles and heart rate (HR) were continuously measured during the tests. In addition, BRUMS questionnaire was applied before and after the tests. Results Significant interactions were found in power and speed (P = 0.001), which were significantly higher at the end of the test (final 2 km) after CAF condition. A main effect of time (P = 0.001) was observed for RPE and HR, which increased linearly until the end of exercise in both conditions. The time taken to complete the test was similar in both conditions (PLA = 2191 ± 158 s vs. CAF = 2181 ± 194 s, P = 0.61). No significant differences between CAF and PLA conditions were identified for speed, power, rpm, RPE, EMG, HR, and BRUMS (P > 0.05). Conclusion The results suggest that caffeine intake 60 min before 20-km time trials has no effect on the performance or physiological responses of cyclists.
Article
The aim of the present study was to investigate the effects of caffeine ingestion on cognitive and physical performances after 36 h of sleep deprivation. In randomized order, thirteen healthy male physical education students (age: 21.1 ± 1.1 years, body mass: 77.1 ± 7.2 kg, height: 1.77 ± 0.06 m) completed four test sessions at 18:00 h: after placebo or 5 mg·kg− 1 of caffeine ingestion during a baseline night (RN) (bed time: from 22:30 h to 07:00 h) or a night of 36 h of sleep deprivation (TSD). During each test session, participants performed the squat jump (SJ), the reaction time, and the 30-s Wingate tests (i.e., for the measurement of the peak (PP) and mean (MP) powers and the fatigue index (FI)). The results showed that PP and MP decreased and FI increased during the TSD compared to RN in the placebo condition (p < 0.001). The caffeine ingestion improved PP after TSD compared to RN (p < 0.001). SJ decreased significantly after the TSD compared to RN after both placebo and caffeine ingestions (p < 0.001). However, SJ increased significantly after caffeine ingestion during RN and TSD (p < 0.001). The reaction time increased significantly after TSD compared to RN (p < 0.001). However, the reaction time decreased significantly after the caffeine ingestion only during the TSD (p < 0.001). Therefore, caffeine is an effective strategy to counteract the effect of 36 h of sleep loss on physical and cognitive performances.
Article
Objectives: To investigate whether coinciding peak serum caffeine concentration with the onset of exercise enhances subsequent endurance performance. Design: Randomised, double-blind, crossover. Methods: In this randomised, placebo-controlled, double-blind crossover study, 14 male trained cyclists and triathletes (age 31±5year, body mass 75.4±5.7 kg, VO₂max 69.5±6.1 mL kg⁻¹ min⁻¹ and peak power output 417±35W, mean±SD) consumed 6 mg kg(-1) caffeine or a placebo either 1h (C(1h)) prior to completing a 40 km time trial or when the start of exercise coincided with individual peak serum caffeine concentrations (C(peak)). C(peak) was determined from a separate 'caffeine profiling' session that involved monitoring caffeine concentrations in the blood every 30 min over a 4h period. Results: Following caffeine ingestion, peak serum caffeine occurred 120 min in 12 participants and 150 min in 2 participants. Time to complete the 40 km time trial was significantly faster (2.0%; p=0.002) in C(1h) compared to placebo. No statistically significant improvement in performance was noted in the C(peak) trial versus placebo (1.1%; p=0.240). Whilst no differences in metabolic markers were found between C(peak) and placebo conditions, plasma concentrations of glucose (p=0.005), norepinephrine and epinephrine (p≤0.002) were higher in the C(1h) trial 6 min post-exercise versus placebo. Conclusions: In contrast to coinciding peak serum caffeine concentration with exercise onset, caffeine consumed 60 min prior to exercise resulted in significant improvements in 40 km time trial performance. The ergogenic effect of caffeine was not found to be related to peak caffeine concentration in the blood at the onset of endurance exercise.