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Journal of Sports Sciences
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The effects of different doses of caffeine on
endurance cycling time trial performance
Ben Desbrow a b , Caren Biddulph a b , Brooke Devlin a b , Gary D. Grant c , Shailendra
Anoopkumar-Dukie c & Michael D. Leveritt a b
a School of Public Health, Griffith University, Queensland, Australia
b Research Centre for Clinical and Community Practice Innovation, Griffith Health Institute,
Griffith University, Queensland, Australia
c School of Pharmacy, Griffith University, Queensland, Australia
Available online: 06 Dec 2011
To cite this article: Ben Desbrow, Caren Biddulph, Brooke Devlin, Gary D. Grant, Shailendra Anoopkumar-Dukie & Michael
D. Leveritt (2011): The effects of different doses of caffeine on endurance cycling time trial performance, Journal of Sports
Sciences, DOI:10.1080/02640414.2011.632431
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The effects of different doses of caffeine on endurance cycling time trial
performance
BEN DESBROW
1,2
, CAREN BIDDULPH
1,2
, BROOKE DEVLIN
1,2
, GARY D. GRANT
3
,
SHAILENDRA ANOOPKUMAR-DUKIE
3
, & MICHAEL D. LEVERITT
1,2
1
School of Public Health, Griffith University, Queensland, Australia,
2
Research Centre for Clinical and Community Practice
Innovation, Griffith Health Institute, Griffith University, Queensland, Australia, and
3
School of Pharmacy, Griffith
University, Queensland, Australia
(Accepted 12 October 2011)
Abstract
This study investigated the effects of two different doses of caffeine on endurance cycle time trial performance in male athletes.
Using a randomised, placebo-controlled, double-blind crossover study design, sixteen well-trained and familiarised male cyclists
(Mean +s:Age¼32.6 +8.3 years; Body mass ¼78.5 +6.0 kg; Height ¼180.9 +5.5 cm _
VO
2peak
¼60.4 +4.1 ml kg
71
min
71
) completed three experimental trials, following training and dietary standardisation. Participants ingested either a
placebo, or 3 or 6 mg kg
71
body mass of caffeine 90 min prior to completing a set amount of work equivalent to 75% of peak
sustainable power output for 60 min. Exercise performance was significantly (P50.05) improved with both caffeine treatments
as compared to placebo (4.2% with 3 mg kg
71
body mass and 2.9% with 6 mg kg
71
body mass). The difference between the
two caffeine doses was not statistically significant (P¼0.24). Caffeine ingestion at either dose resulted in significantly higher
heart rate values than the placebo conditions (P50.05), but no statistically significant treatment effects in ratings of perceived
exertion (RPE) were observed (P¼0.39). A caffeine dose of 3 mg kg
71
body mass appears to improve cycling performance in
well-trained and familiarised athletes. Doubling the dose to 6 mg kg
71
body mass does not confer any additional
improvements in performance.
Keywords: Athletes, dose-response relationship, glucose, exercise, endurance, methylxanthine
Introduction
The ergogenic potential of caffeine on endurance
performance tasks lasting approximately 1 hr have
been well documented and summarised in a number
of recent reviews (Burke, 2008; Doherty & Smith,
2004; Ganio, Klau, Casa, Armstrong, & Maresh,
2009). Caffeine has been shown to be ergogenic in
studies using a wide variety of dosing protocols
(Doherty & Smith, 2004; Ganio et al., 2009). The
optimal dose of caffeine required to elicit maximal
high intensity endurance performance under relevant
conditions (i.e. using valid performance tasks and
when fed) is of interest to many athletes.
Early dose-response studies (Graham & Spriet,
1995; Pasman, vanBaak, Jeukendrup, & deHaan,
1995) suggested a bolus dose of 3–6 mg kg
71
body
mass of caffeine provided 1 hr prior to exercise was
ideal to improve endurance performance of approxi-
mately one hour duration. Graham and Spriet
(1995) found that both low and moderate (3
mg kg
71
and 6 mg kg
71
body mass) doses of
caffeine resulted in similar enhancements in running
time to exhaustion, however, a higher dose of
caffeine (9 mg kg
71
body mass) did not have a
significant impact on performance as compared to
placebo, despite having the greatest effect on
epinephrine and blood-borne metabolite levels (Gra-
ham & Spriet, 1995). Pasman et al. (1995) also
demonstrated improvements in performance (cy-
cling) compared to placebo with 5 mg kg
71
body
mass of caffeine but no further improvements with 9
or 13 mg kg
71
body mass doses, respectively. In
both of these studies however, less than 10 partici-
pants were used and time-to-exhaustion protocols
were employed. Time-to-exhaustion protocols have
been suggested to better serve as tests of exercise
capacity rather than absolute performance (Burke,
2008) whereas protocols based on fixed end point
tasks, or time-trials have greater ecological validity
Correspondence: Ben Desbrow, School of Public Health and Research Centre for Clinical and Community Practice Innovation, Griffith Health Institute,
Griffith University, Gold Coast Campus, Queensland 4222, Australia. E-mail: b.desbrow@griffith.edu.au
Journal of Sports Sciences, 2011; 1–6, iFirst article
ISSN 0264-0414 print/ISSN 1466-447X online Ó2011 Taylor & Francis
http://dx.doi.org/10.1080/02640414.2011.632431
Downloaded by [Griffith University] at 15:30 08 December 2011
(Currell & Jeukendrup, 2008), and appear to be
highly reproducible (Jeukendrup, Saris, Brouns, &
Arnold, 1996).
Caffeine’s ergogenic effects on 30–60 min cycling
time trial performance may also be seen at substan-
tially lower doses (i.e., 3mgkg
71
body mass)
(Jenkins, Trilk, Singhal, O’Connor, & Cureton,
2008; Kovacs, Stegen, & Brouns, 1998). Kovacs
and colleagues (1998) demonstrated improved one
hour time trial cycling performance compared to
placebo in 14 well trained and fed participants given
a total of 2.1 mg kg
71
body mass of caffeine.
Further enhancements were then observed with 3.2
mg kg
71
. However 4.5 mg kg
71
body mass of
caffeine provided no additional benefits over 3.2
mg kg
71
body mass. The caffeine ingestion proto-
col involved the caffeine being mixed within a
carbohydrate-electrolyte solution which was con-
sumed prior to and throughout the exercise task
(Kovacs et al., 1998).
More recently a dose-response study by Jenkins
et al., (2008) observed no significant performance
benefits when 1 mg kg
71
body mass of caffeine was
given to 13 fasted participants one hour before a 30
minute cycling exercise task (15 min @ 80%
_
VO
2
þ15 min time trial). However, when partici-
pants were provided with slightly higher caffeine
doses (i.e., 2 and 3 mg kg
71
body mass) a similar
performance improvement was observed (4% and
3% improvement, respectively) (Jenkins et al., 2008).
Taken together, these two studies suggest that
caffeine is ergogenic in a dose-dependent manner up
to 3 mg kg
71
body mass, with no additional gains
in performance from doses 43mgkg
71
body
mass. Both of these studies however, neglected to
include a higher caffeine dose for comparison
delivered as a bolus prior to exercise consistent with
the earlier dose-response studies employing the time-
to-fatigue protocols. Hence it is therefore difficult to
determine an optimal pre-exercise caffeine dose
under sports specific conditions without using a
higher dose for comparison.
Thus the purpose of this investigation was to
determine the effects of two clearly contrasting pre-
exercise bolus doses of caffeine on the performance
of a 1 hr cycle time trial in well-trained and fed
athletes. It was hypothesised that caffeine would
improve endurance performance, compared with a
placebo, but that there would be no greater benefits
gained with the use of higher doses.
Methods
The study was carried out with approval from the
Human Research Ethics Committee of Griffith
University, Queensland, Australia.
Participants
Sixteen well-trained male cyclists (Mean +s:
Age ¼32.6 +8.3 years; Body mass ¼78.5 +6.0 kg;
Height ¼180.9 +5.5 cm _
VO
2peak
¼60.4 +4.1 ml
kg
71
min
71
) volunteered to participate in the
study.
Preliminary testing
Participants attended the laboratory on three occa-
sions prior to the experimental trials. The first visit
included medical screening, a questionnaire regard-
ing their habitual caffeine consumption (mean
210 +115 mg d
71
, range 10–600 mg d
71
), and
an incremental exercise test to exhaustion on an
electronically-braked cycle ergometer (Lode Excali-
bur Sport, Lode, Groningen, The Netherlands), to
determine participants’ individual _
VO
2peak
values
(ml kg
71
min
71
) and peak power outputs (Des-
brow, Barrett, Minahan, Grant, & Leveritt, 2009).
Two familiarisation sessions involving the full
exercise protocol followed, in which a self-selected
warm-up and individual linear factors were estab-
lished.
Standardisation of conditions
Participants were asked to abstain from all dietary
sources of caffeine, alcohol and strenuous exercise
for the 24 hr preceding each experimental trial.
Participants consumed a pre-packaged standardised
diet (200 kJ kg
71
body mass, including 7.5 g kg
71
body mass of carbohydrate for the 24 hr preceding
each experimental trial and compliance with the
exercise and dietary controls was confirmed verbally
on the morning of each trial prior to testing. A light
pre-exercise meal (42 kJ kg
71
body mass, including
2gkg
71
body mass of carbohydrate) was provided
on the morning of the trials. Additionally participants
ingested 3 ml kg
71
body mass of 6% carbohydrate-
electrolyte beverage during the warm-up, as well as
upon completion of 30% and 60% of the target
amount of work. To avoid any influence of circadian
variance, experimental trials were performed at the
same time of the day (mornings), with a 7 day wash-
out period between each session. Trials were
conducted in the same laboratory, on the same
ergometer, under stable environmental conditions
(*19–208C, *55% relative humidity).
Experimental trials
Each participant completed three time trials, in
random order, under double-blind conditions. Par-
ticipants reported to the laboratory approximately 2
hr before trials and after consuming the pre-exercise
2B. Desbrow et al.
Downloaded by [Griffith University] at 15:30 08 December 2011
meal, a resting 5 ml blood sample was taken via
forearm venipuncture for subsequent analysis of
plasma caffeine. At 90 min prior to the trials,
participants ingested four opaque capsules contain-
ing either pure anhydrous caffeine (equivalent to 3
mg kg
71
body mass of caffeine (low dose caffeine)
or 6 mg kg
71
body mass of caffeine (high dose
caffeine)) or the placebo treatment containing
approximately 400 mg of Metamucil
1
(100% psy-
llium husk fibre). After resting in a thermo-neutral
environment, each participant performed a standar-
dised warm-up and immediately prior to the
commencement of the time trial, another venous
blood sample (5 ml) was collected.
The time trial was performed with the ergometers
set in linear mode. The participants’ linear factors
were determined on an individual basis (during
familiarisation) depending on their peak power
outputs and were initially chosen so that 75% peak
power output could be achieved at *100 rpm, which
was the preferred cadence for most cyclists. Partici-
pants were required to perform a set amount of work
as fast as possible. The target amount of work was
calculated according to the formula:
Total work ðJÞ¼0:75 Peak Power Output 3600
The same researcher supervised each time trial
and provided standardised feedback to each partici-
pant. Subjective ratings of perceived exertion (RPE)
(Borg, 1982) and heart-rate (HR) values (Polar
Electro, Kempele, Finland) were recorded at each
10% of the time trial. Participants were able to view
their HR, cadence and power output for the first
10% of the time trial only. After completion of the
first 10% the only information available to partici-
pants was elapsed work as a percentage of the final
work. No gas exchange data or blood samples were
collected during the time trial. A final blood sample
(5 ml) was taken immediately post-exercise for the
analysis of plasma caffeine.
Upon completion of all three trials, participants
were asked to attempt to identify the order of treatment
for the trials, and to judge which trial they perceived to
be representative of their best performance.
Blood sampling, storage and analysis
Venous blood (5 ml) was sampled before supple-
mentation and immediately prior to-, and post-
exercise. Samples were kept in lithium heparin
vacutainers, before being centrifuged at 4000 rpm
for 10 min at 58C. Plasma was then extracted and
stored at 7848C until subsequent analysis.
The quantitative analysis of plasma caffeine was
performed using an automated ‘‘reversed-phase’’
high-performance liquid chromatography system,
with conditions adapted with subtle modifications
from Koch, Tusscher, Kopple and Guchelaar
(1999). The precise method has been previously
described (Desbrow et al., 2009). Plasma glucose
was determined in duplicate using a commercial
glucose analysis kit according to the manufacturer’s
specifications on an automated blood biochemistry
analyser (Cobas Integra 400, Roche Diagnostics,
Switzerland).
Data analysis
Statistically significant differences were accepted at
the 5% level. All dependent measures were analysed
using repeated measures ANOVA exploring dose
and time interactions. Where significant main effects
were observed pair-wise (Bonferroni) comparisons
were conducted to identify the specific nature of the
differences. In addition, inferential statistics based
on 95% confidence limits, were used to assess the
clinical utility and practical applicability of results
(Hopkins, 2000). The magnitude of the smallest
worthwhile change in time trial performance was
assumed to be an improvement/decrement in time to
complete the set amount of work by 41% (when
trials performed under conditions of caffeine treat-
ment are compared to those performed under
placebo conditions), based on the coefficient of
variation (CV) derived from Laursen, Shing and,
Jenkins (2003) using familiarised participants. The
magnitude of the effect of caffeine was expressed
using Cohen-type effect sizes and interpreted using a
modified, performance-based scale (Hopkins, 2000).
All results are reported as means +s.
Results
Standardisation procedures
Mean 24 hr pre-trial energy and carbohydrate intakes
were 195.90 +18.47 kJ kg
71
body mass and
7.15 +0.70 g kg
71
body mass, respectively. Parti-
cipants reported no alcohol or tobacco use in the 24
hr prior to each trial. No strenuous exercise was
reportedly undertaken during the 18 hr period before
each trial. All participants complied with the
instructions regarding the consumption of the
carbohydrate-electrolyte beverages during the trials
(707 +54 ml), and all drinks were well-tolerated.
Plasma caffeine and glucose
All participants commenced trials without measur-
able plasma caffeine (Figure 1) indicating a period of
acute caffeine-abstinence was achieved. The plasma
concentrations of caffeine rose rapidly following
caffeine ingestion and both doses resulted in plasma
Different doses of caffeine on cycling performance 3
Downloaded by [Griffith University] at 15:30 08 December 2011
caffeine levels significantly different from placebo.
Mean plasma caffeine levels were significantly higher
for the high dose caffeine treatment, compared to the
low dose caffeine treatment prior to exercise
(35.18 +16.50 mmol l
71
and 16.35 +7.57 mmol
l
71
respectively; P50.05), and post-exercise
(37.98 +15.90 mmol l
71
and 17.74 +6.04 mmol
l
71
respectively; P50.05). Plasma glucose
values are provided in Table I. Irrespective of
the trial, mean plasma glucose levels fell within the
pre-ingestion to pre-exercise period (P50.05)
but returned to pre-ingestion levels at the comple-
tion of exercise. Caffeine dose did not influence
plasma glucose responses except for an elevated
plasma glucose measure in the high dose caffeine
trial compared to placebo following exercise
(P50.05).
Time trial performance, RPE and HR
The mean time trial times for the placebo, low dose
caffeine and high dose caffeine trials were
3902 +340 s, 3738 +286 s and 3791 +281 s,
indicating significant performance improvements in
the caffeine containing trials (4.21% with low dose
caffeine (P50.05) and 2.84% with high dose
caffeine (P50.05)). The mean difference between
the low dose caffeine and high dose caffeine trials was
not statistically significant (P¼0.24) (Table II).
Twelve of 16 (75%) participants produced their
slowest time trial performance on placebo with the
remaining four participants producing their slowest
time trial on high dose caffeine trials. Nine of the
participants (56%) produced their best performance
on low dose caffeine whereas five (31%) produced
their best time on the high dose caffeine trial.
Caffeine ingestion at either dose resulted in
significantly higher mean HR values as compared
to placebo conditions (P50.05), but there was no
significant difference in mean HR between the two
caffeine trials (P¼0.34). No statistically significant
differences in RPE values between any of the
treatment conditions at any time point were noted
(P¼0.39).
Post trial investigations
Six of the 16 participants (38%) correctly identified
the treatment order of all three trials and five
participants (31%) could distinguish when they had
received the placebo treatment, but were unable to
differentiate between the two caffeine trials. The
majority (n¼12; 75%) believed that they performed
better when caffeine was ingested and more than half
(n¼9; 56%) of the participants correctly identified
their fastest time trial.
Discussion
The purpose of this investigation was to determine
the effects of two contrasting pre-exercise bolus
doses of caffeine on the performance of a one hour
cycle time trial. The results of this study indicate that
caffeine is ergogenic to endurance cycling perfor-
mance, with statistically significant enhancements in
time trial times of 4.2% for low dose caffeine and
2.9% for high dose caffeine when compared to
placebo. The magnitude of the effects demonstrated
in this study appear to be consistent with data from
previous studies using cycle time trials of 30–60 min
duration which have demonstrated performance
improvements ranging between 1.8–5.8% (Jenkins
et al., 2008; Kovacs et al., 1998; McNaughton et al.,
2008).
Two previous studies suggested that caffeine was
ergogenic in a dose-dependent manner up to 3
mg kg
71
body mass, with no additional gains in
performance from doses 43mgkg
71
body mass
(Jenkins et al., 2008; Kovacs et al., 1998). However,
the highest dose ingested within these studies was 4.5
mg kg
71
body mass of caffeine administered prior
Figure 1. Plasma caffeine concentration prior to and post time trial
following ingestion of 0, 3 and 6 mg kg
71
body mass of caffeine.
Values are mean +s(n¼16). Placebo (PLA) ¼0mgkg
71
body
mass, Low Dose Caffeine (LDC) ¼3mgkg
71
body mass of
caffeine, High Dose Caffeine (HDC) ¼6mgkg
71
body mass of
caffeine.
a
denotes significant difference between all caffeine doses.
Table I. Plasma Glucose (mmol l
71
) following ingestion of 0, 3
and 6 mg kg
71
body mass of caffeine.
Treatment Pre-Ingestion Pre-Exercise Post-Exercise
PLA 6.3 +1.1 3.9 +1.0 5.6 +0.9
LDC 5.8 +1.3 4.2 +1.2 6.1 +1.2
HDC 5.7 +1.4 4.5 +1.3 6.4 +1.2
a
All values are means +s. Placebo (PLA) ¼0mgkg
71
body
mass, Low Dose Caffeine (LDC) ¼3mgkg
71
body mass of
caffeine, High Dose Caffeine (HDC) ¼6mgkg
71
body mass of
caffeine.
a
denotes significantly different value compared to PLA.
4B. Desbrow et al.
Downloaded by [Griffith University] at 15:30 08 December 2011
to and throughout the performance task. The results
of the present study provide further support that a
moderate pre-exercise caffeine dose (3 mg kg
71
body mass) is equally effective as a higher caffeine
dose (6 mg kg
71
body mass) at improving perfor-
mance in fed and familiarised athletes.
The present findings are also consistent with
earlier research using ‘‘time to fatigue’’ type proto-
cols in that the higher doses of caffeine (46–9
mg kg
71
body mass) were associated with no
additional performance improvements (Graham &
Spriet, 1995; Pasman et al., 1995). Indicating that
caffeine’s ergogenic potential exists in tests designed
to reflect measures of exercise performance. There-
fore we now have greater confidence that the optimal
ergogenic dose is *3mgkg
71
body mass for this
type of exercise task.
Given that plasma caffeine increases proportionate
to the dose administered, the current results and
those of the recent meta-analysis (Conger, Warren,
Hardy, & Millard-Stafford, 2011) indicate that the
ergogenic potential of caffeine is unlikely to be
related to higher levels of plasma caffeine in
circulation. Indeed, Cox et al. (2002) initially
demonstrated that small amounts of caffeine in-
gested in the form of a cola beverage had the
potential to enhance cycling time trial performance
despite eliciting only a very small increase in plasma
caffeine. Given that higher caffeine doses are also
more likely to result in adverse side-effects (Nawrot
et al., 2003), clearly lower doses of caffeine have
greater practical application for tasks of this duration.
Whilst many studies have demonstrated ergogenic
effects associated with caffeine ingestion the possibi-
lity of known placebo effects associated with caffeine
ingestion (Beedie, Stuart, Coleman, & Foad, 2006)
must also be considered within the current study.
Although the treatments were administered in a
double-blind manner, the majority of participants
(11/16) correctly identified the placebo trials at the
conclusion of the study. Hence there is the potential
that the participant’s awareness of an ‘‘active’’
intervention may have influenced subsequent per-
formance. Nevertheless the performance improve-
ment of 4.2% in the low dose caffeine treatment is
somewhat greater than the magnitude of previously
documented placebo effects (Beedie et al., 2006).
The current proposed ergogenic mechanisms of
caffeine can be categorised by possible interrelated
effects along two major themes i) central effects
mediated via adenosine receptor antagonism, and ii)
direct effects on skeletal muscle via influence on
muscle electrolyte homeostasis (primarily Ca
2þ
and
K
þ
) (Tarnopolsky, 2010). Given the protocol in the
current study was selected to reflect competition
environments (a self-paced time trial), the ability to
elucidate further on possible ergogenic mechanisms
is limited. As anticipated, HR values increased
following caffeine ingestion in accordance with
observations from other studies (Bridge & Jones,
2006; Cole et al., 1996). Additionally the RPE data
confirmed that participants appear able to exercise at
higher absolute intensities for a given rate of exertion
supporting the theory that alteration in neural
perception of effort may be one mechanism by which
caffeine exerts its ergogenic effects (Doherty &
Smith, 2005). Irrespective of the mechanism(s)
involved the results of the present study confirm
that high levels of plasma caffeine are not required to
trigger the ergogenic responses within this type of
exercise task.
Conclusion
The results of the study demonstrate that caffeine at
either 3 or 6 mg kg
71
body mass is beneficial to 1
hr cycling time trial performance. However greater
levels of circulating caffeine resulting from the higher
dose do not equate to better performance outcomes.
Practical application
Athletes planning to use caffeine for events of *1
hr duration are best advised to use a moderate
Table II. Results of time trial following ingestion of 0, 3 and 6 mg kg
71
body mass of caffeine.
Treatment Comparison
Mean improvement (s) +s
95% Confidence Limits Cohen’s Effect Size
Qualitative outcome
(P
beneficial/
P
trivial
/P
harmful
)
LDC-PLA 164.3 +64.1
a
(55.2 to 273.5) 0.51 Almost certainly beneficial
(100/0/0)
HDC-PLA 110.8 +83.5
a
(1.6 to 219.9) 0.35 Probably beneficial
(92/7/0)
LDC-HDC 753.6 +77.4 (7162.7 to 55.59) 0.17 Possibly harmful
(3/53/63)
Possibly harmful
(3/53/63)
Time trial values are means +s. Placebo (PLA) ¼0mg kg
71
body mass, Low Dose Caffeine (LDC) ¼3mgkg
71
body mass of caffeine,
High Dose Caffeine (HDC) ¼6mgkg
71
body mass of caffeine.
a
denotes significant differences compared to PLA.
Different doses of caffeine on cycling performance 5
Downloaded by [Griffith University] at 15:30 08 December 2011
pre-exercise caffeine dose (*3mgkg
71
body
mass) to maximise the ergogenic potential whilst
minimising possible side-effects.
Acknowledgements
We would like to thank Dr. S. Sabapathy, Ms. L.
Ball, Ms. E. Stephens and Ms. A. Quinlivan who all
assisted in various aspects of the data collection and
the cycling participants for their contributions to this
research.
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