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The Metabolic and Performance Effects of Caffeine
Compared to Coffee during Endurance Exercise
Adrian B. Hodgson
1
, Rebecca K. Randell
1
, Asker E. Jeukendrup
1,2
*
1Human Performance Laboratory, School of Sport and Exercise Science, University Of Birmingham, Birmingham, United Kingdom, 2Gatorade Sport Science Institute,
PepsiCo, Barrington, Illinois, United States of America
Abstract
There is consistent evidence supporting the ergogenic effects of caffeine for endurance based exercise. However, whether
caffeine ingested through coffee has the same effects is still subject to debate. The primary aim of the study was to
investigate the performance enhancing effects of caffeine and coffee using a time trial performance test, while also
investigating the metabolic effects of caffeine and coffee. In a single-blind, crossover, randomised counter-balanced study
design, eight trained male cyclists/triathletes (Mean6SD: Age 4167y, Height 1.8060.04 m, Weight 78.964.1 kg, VO
2
max
5863mlNkg
21
Nmin
21
) completed 30 min of steady-state (SS) cycling at approximately 55% VO
2
max followed by a 45 min
energy based target time trial (TT). One hour prior to exercise each athlete consumed drinks consisting of caffeine (5 mg
CAF/kg BW), instant coffee (5 mg CAF/kg BW), instant decaffeinated coffee or placebo. The set workloads produced similar
relative exercise intensities during the SS for all drinks, with no observed difference in carbohydrate or fat oxidation.
Performance times during the TT were significantly faster (,5.0%) for both caffeine and coffee when compared to placebo
and decaf (38.3561.53, 38.2761.80, 40.2361.98, 40.3161.22 min respectively, p,0.05). The significantly faster performance
times were similar for both caffeine and coffee. Average power for caffeine and coffee during the TT was significantly
greater when compared to placebo and decaf (294621 W, 291622 W, 277614 W, 276623 W respectively, p,0.05). No
significant differences were observed between placebo and decaf during the TT. The present study illustrates that both
caffeine (5 mg/kg/BW) and coffee (5 mg/kg/BW) consumed 1 h prior to exercise can improve endurance exercise
performance.
Citation: Hodgson AB, Randell RK, Jeukendrup AE (2013) The Metabolic and Performance Effects of Caffeine Compared to Coffee during Endurance Exercise. PLoS
ONE 8(4): e59561. doi:10.1371/journal.pone.0059561
Editor: Conrad P. Earnest, University of Bath, United Kingdom
Received November 26, 2012; Accepted February 15, 2013; Published April 3, 2013
Copyright: ß2013 Hodgson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The authors have no funding or support to report.
Competing Interests: AEJ is employed by Pepsi Co. There are no patents, products in development or marketed products to declare. This does not alter the
authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.
* E-mail: a.e.jeukendrup@bham.ac.uk
Introduction
Numerous studies to date have shown that caffeine ingested
prior to [1–7] and during [8] prolonged sub-maximal and high
intensity exercise can improve performance. Since the seminal
work by Costill and colleagues [9] it is often cited that caffeine
induces its ergogenic effects by an increase in fat oxidation through
the sympathetic nervous system, and a sequential sparing of
muscle glycogen [2]. However, there is very little support for an
increase in fat oxidation [10,11] or an enhancement to the
sympathetic nervous system [12] being the principal mechanism of
caffeine’s ergogenic effect. Since, recent investigations have
elucidated that the principal mechanism of caffeine’s ergogenic
effects is through its ability to act as an adenosine receptor
antagonist to induce effects on both central and peripheral nervous
system [13] to reduce pain and exertion perception [14], improve
motor recruitment [13] and excitation-contraction coupling [15–
17].
In the literature to date, the ergogenic effects are well
documented with the time to exhaustion test at a fixed power
output being the predominant performance measure used [1,2,9–
11]. It was questioned whether assessing endurance capacity in this
way would have sufficient ecological validity to translate results to
real life events [18]. However since then, a number of studies have
confirmed the ergogenic effects of caffeine using time trial
protocols [3–5,7,8], which involves completing an energy based
target or set distance in as fast as time possible, thus simulating
variable intensities that are likely to occur during competitive
events. In most of these studies pure (anhydrous) caffeine was
ingested through capsules or dissolved in water. Based on this
research it is often assumed that ingesting caffeine in a variety of
dietary sources, such as coffee, will result in the same ergogenic
effect.
Very few studies, however, have shown a positive effect of coffee
on exercise performance. Coffee improved performance in some
[9,19–21], but not all studies [22–24]. This may seem surprising as
reports have shown that coffee is the most concentrated dietary
source of caffeine as well as being one of the largest sources of
caffeine used by athletes prior to competition [25]. Amongst the
current studies, only two investigations have actually used coffee
rather than decaffeinated coffee plus anhydrous caffeine [21,22],
with only one of these studies showing an ergogenic effect of the
coffee [21]. This further identifies the equivocal evidence
surrounding the performance effects of coffee. The most cited
study is perhaps a study by Graham et al [22], who showed that
running time to exhaustion (85% VO
2
max) was only improved
when runners ingested pure caffeine (4.5 mg CAF/kg BW), prior
to exercise, but not when they ingested either regular coffee
PLOS ONE | www.plosone.org 1 April 2013 | Volume 8 | Issue 4 | e59561
(4.5 mg CAF/kg BW), decaffeinated coffee plus caffeine (4.5 mg
CAF/kg BW), decaffeinated coffee and a placebo control. The
authors reported that the difference in performance could not be
explained by the caffeine or methylxanthine plasma concentra-
tions 1 h following intake or at end of exercise, as no difference
was observed between trials that contained caffeine.
Graham et al [22] suggested that other components in coffee
known as chlorogenic acids, may have antagonised the physiolog-
ical responses of caffeine. However, in this study [22] chlorogenic
acids in the coffee or in the plasma were not measured.
Chlorogenic acids are a group of phenolic compounds that possess
a quinic acid ester of hydroxycinnamic acid [26]. The consump-
tion of chlorogenic acids varies significantly in coffee ranging from
20–675 mg per serving [26]. It has previously been shown in vitro
that chlorogenic acids antagonize adenosine receptor binding of
caffeine [27] and cause blunting to heart rate, blood pressure and
cause a dose-dependent relaxation of smooth muscle [28]. For this
reason, it is unclear what role chlorogenic acids, found in coffee,
will have on the physiological and metabolic effects of coffee and
caffeine during exercise in humans. Therefore, due to the large
variation of chlorogenic acids between coffee beverages and the
unclear performance effects of coffee to date, it is yet to be
determined if coffee causes differences in the performance and
metabolic effects during exercise when compared to caffeine alone.
Therefore the primary aim of the present study was to
investigate whether acute intake of coffee (5 mg CAF/kg BW)
and anhydrous caffeine (5 mg CAF/kg BW) are ergogenic to
cycling performance compared to decaffeinated coffee or placebo
beverages when using a validated 45-minute time trial perfor-
mance test. In addition, completing a steady state exercise bout
prior to the time trial performance test is a routine protocol used in
our laboratory [18,29]. For this reason it provided any opportunity
to also investigate the effect of acute anhydrous caffeine or coffee
intake on substrate oxidation and plasma metabolite responses
during 30-min steady state exercise (55% VO
2
max). The study
hypothesis was that despite the previous work by Graham et al
[22], 5 mg CAF/kg BW regardless of the form of administration
(anhydrous or coffee) would be ergogenic to performance similarly
when compared to decaffeinated coffee or placebo, but this effect
would not be mediated through changes in fat metabolism.
Materials and Methods
Participants
Eight trained cyclists/triathletes (Mean 6SD: Age 4167y,
Height 1.8060.04 m, Weight 78.964.1 kg, _
VVO
2max
5863mlNkg
21
Nmin
21
) were recruited from local Birmingham
cycling and triathlon clubs. Inclusion criteria included participants
who trained 3 or more times per week (.90-min/session), had
been training for .2 years, and had a low habitual caffeine intake
of #300 mg/d (approximately #3 cups coffee/d).
Ethics statement
All participants were fully informed of the experimental trials
and all risks and discomforts associated before providing written
informed consent to participate in the study. All procedures and
protocols were approved by the Life and Environmental Sciences
Ethical Review Committee at the University of Birmingham.
General Study design
The study followed a single blinded, cross over, randomised
counter-balanced study design. Maximal oxygen uptake
(_
VVO
2max) and power (Wmax) was assessed during a preliminary
trial. Following this each participant completed 4 experimental
trials, each separated by 7 days. Each trial consisted of consuming:
caffeine (5 mg CAF/kg BW) (CAF), coffee (5 mg CAF/kg BW)
(COF), decaffeinated coffee (DECAF) or placebo (PLA) in the
overnight fasted state (8 hrs) 1 h before completing 30-min steady
state cycle exercise bout (SS) (55% _
VVO
2max). Following this each
participant was instructed to complete a time trial lasting
approximately 45-min.
Preliminary Trial
Before the experimental trial, participants visited the Human
Performance Laboratory at the University of Birmingham on two
separate occasions separated by 7 days. During the first visit
participants completed an incremental exercise test on an
electronically braked cycle ergometer (Lode Excalibur Sport,
Groningen, Netherlands) to volitional exhaustion ( _
VVO
2max test).
Prior to beginning the test participants firstly had weight (OHaus,
Champ II scales, USA) and height (Seca stadiometer, UK)
recorded. Participants mounted the cycle ergometer, which was
followed by a 5-min warm up at 75 W, participants then started
the test at 95 W for 3-min. The resistance was increased every 3-
min, in incremental steps of 35 W, until they reached voluntary
exhaustion. Wmax was calculated using the following equation:
Wmax ~Woutzt=180ðÞ|35½
Where W
out
is the power output of the last stage completed
during the test, and t is the time spent, in seconds, in the final
stage. Throughout the test respiratory gas measurements ( _
VVO
2
and _
VVCO
2) were collected continuously using an Online Gas
Analyser (Oxycon Pro, Jaeger). _
VVO
2was considered maximal if 2
out of the 4 following criteria were met: 1) if _
VVO
2levelled off even
when workload increased 2) a respiratory exchange ratio (RER) of
.1.05 3) a heart rate within 10 beats/min of age predicted
maximal heart rate 4) a cadence of 50 rpm could not be
maintained. Heart rate (HR) was recorded during each stage of
the test using a HR monitor (Polar, Warwick, UK). Wmax was
used to determine the work load for the steady state exercise bouts
throughout all subsequent experimental trials (50% W
max
). Wmax
was also used to calculate the total amount of work to be
completed during the 45-min time trial and the linear factor, both
calculated according to the formula derived by Jeukendrup et al
[18]. The bike position was recorded following the test to be
replicated in all other trials.
Approximately 7 days later participants reported back to the
lab, for the second preliminary trial, between 0600 and 0800
having undergone an 8 hr fast. The purpose of the trial was to
familiarise each subject to the experimental trial and time trial
protocol. All participants completed 30-min SS at 50% W
max
(55% _
VVO
2max). Expired breath samples were collected every 10-
min for measures of _
VVO
2
,
_
VVCO
2
,
and RER (Oxycon Pro, Jaeger).
Immediately following all participants completed a time trial
lasting ,45 min. The data collected during the familiarisation trial
was not used for any of the final analysis.
Experimental Trial
All participants reported to the Human Performance Lab
between 0600 and 0800 having completed an 8 h overnight fast.
On arrival weight was recorded (Seca Alpha, Hamburg, Germany)
and a flexible 20-gauge Teflon catheter (Venflon; Becton
Dickinson, Plymouth, United Kingdom) was inserted into an
antecubital vein. A 3-way stopcock (Connecta; Becton Dickinson)
was attached to the catheter to allow for repeated blood sampling
Caffeine and Coffee on Exercise Performance
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during the experimental period. An initial 15 ml fasting blood
sample was collected (EDTA-containing tubes, BD vacutainers).
Following this all participants consumed one of the treatment
beverages and rested for 1 h, with further samples taken at 30 min
and 60 min (10 ml EDTA). After the rest period, participants then
mounted the cycle ergometer, in an identical bike position as
recorded during the preliminary trial, and began a 30-min SS at
50% W
max
(55% _
VVO
2max). Blood samples (15 ml) and 5-min
respiratory breath samples, VO
2
, VCO
2
and RER, (Oxycon Pro,
Jaeger) were collected every 10-min during the exercise. The
catheter was kept patent during both the rest and exercise period
by flushing it with 5 mL isotonic saline (0.9% w/v; B Braun) after
every blood sample. In addition, heart rate (HR) was recorded
(Polar RS800CX) every 15 min at rest and every 10 min during
SS. Ratings of Perceived Exertion (RPE) scale were recorded every
10 min during SS using the 6–20 Borg scale [30]. Upon
completion of the SS, the subject was instructed to stop exercising
for ,1 min, and the cycle ergometer was set in the linear mode.
The participants were instructed to complete an energy-based
target amount of work at 70% W
max
in the quickest time possible.
The total amount of work (650637 KJ) was calculated for the
45 min time trial. A linear factor, 70% W
max
divided by (90 rpm)
2
was entered into the cycle ergometer. The time trial protocol
employed has previously been validated and has been shown to be
highly reliable [18]. Participants received a countdown prior to
starting the time trial and received no verbal or visual feedback
regarding performance time or physiological measures throughout
the test. No additional measures, blood or respiratory, were taken
through the test. Participants received no feedback about their
performance until they had completed all 4 experimental trials.
Following the completion of the TT, each participant completed a
questionnaire to guess the test beverage consumed prior to the
commencement of the trial, as well as report any GI distress
experienced during the trial.
Treatment Beverages
During each visit to the lab, participants ingested one of four
treatment beverages. This included caffeine (5 mg CAF/kg BW),
regular coffee (5 mg CAF/kg BW), decaffeinated coffee and
placebo. Therefore decaffeinated coffee and placebo acted as
controls to both of the caffeinated trials. Caffeine (Anhydrous
caffeine, 99.8% pure, Blackburn Distributions Ltd, Nelson, United
Kingdom) was weighed (394.467.0 mg) prior to the trial, and was
immediately dissolved and vortexed for 15 min in 600 ml of water
prior to consumption and served in an opaque sports drinks bottle.
Coffee was prepared using instant coffee (Nescafe Original). In
order to select the correct weight of coffee to equal 5 mg CAF/kg
BW, Nescafe states that Nescafe Original instant coffee provides
3.4 g caffeine/100 g of instant coffee. This information was
confirmed using a HPLC method (see below), and based on the
analysis it was calculated that 0.15 g coffee/kg/BW equalled 5 mg
CAF/kg BW. Therefore prior to each trial, coffee was weighed
(11.861.0 g) and dissolved in 600 ml hot water (9462uC) and
served in a mug.
DECAF (Nescafe Original Decaffeinated coffee, ,97% caffeine
free) was prepared in an identical fashion, with the same amount
of decaffeinated coffee as the COF beverage. Using a HPLC
method, decaffeinated coffee provided minimal caffeine through-
out each of the prepared beverages (0.17 mg CAF/kg BW or
mean intake of 13.4160.70 mg). In order to blind the participants
from the taste of the caffeine trial, the placebo trial consisted of
8 mg of Quinine sulphate (Sigma, UK). Quinine sulphate is a food
ingredient found in tonic water to give a bitter taste. The quinine
sulphate was dissolved in 600 ml of water, vortexed for 15 min,
and served in an opaque sports drinks bottle. The exact dose of
quinine sulphate was preliminary tested in our lab. A dose of 8 mg
was sufficient to prevent the blinded researchers from distinguish-
ing between the placebo and caffeine trial.
The coffee and decaffeinated coffee samples were further
analysed externally for chlorogenic acids (5-CQA) (Eurofins
Scientific, Italy). Based on the analysis, total 5-CQA was
33.91 mg/g and 28.29 mg/g for COF and DECAF respectively.
This was then used to calculate the average concentration of total
5-CQA and related isomers for each participants drinks, based on
the weight of instant COF and DECAF. The average chlorogenic
acid intake in COF and DECAF are presented in Table 1. All of
the beverages were prepared in 600 ml of water. This was firstly to
avoid any difference in uptake and bioavailability of each of the
ingested ingredients, as well as replicating the format of coffee
consumption from everyday life. Secondly 600 ml of coffee
dissolved in water was not only considered tolerable, based on
taste testing by researchers within our laboratory, but also
matched similar volumes as used by Graham et al [22]. Once
participants received each of the beverages at the beginning of the
trial, they had 15 min to consume the entire 600 ml.
Diet and Exercise Control
Participants were instructed to record their food intake the day
prior to the preliminary familiarisation trial. Participants had to
replicate this diet in the 24 h prior to each experimental trial, as
well as refraining from any exercise, consume no alcohol and
withdraw from any caffeinated products.
Calculations
Substrate metabolism was measured during the SS. From the
respiratory output measurements of _
VVO
2and _
VVCO
2(L/min),
carbohydrate [1] (CHO) and fat oxidation [2] was calculated
every 10 min during the SS. In order to calculate CHO and fat
oxidation stoichiometric equations [31] were used, which assume
that each of the participants were exercising at a steady state and
that protein oxidation was negligible.
1½~4:210 _
VVCO
2{2:962 _
VVO
2
2½~1:65 _
VVO
2{1:701 _
VVCO
2
Blood Analysis
Following collection, all tubes were placed in ice until the end of
the experimental trial. Following this each tube was centrifuged at
3500 rpm for 15 min at 4uC. Aliquots of plasma were immediately
frozen in liquid nitrogen and stored at 280uC for later analysis.
Each blood sample taken throughout each experimental trial were
analysed for plasma glucose (Glucose Oxidase; Instrumentation
Laboratories, England), fatty acids (FA) [NEFA-C; Randox,
England], glycerol (Glycerol; Randox, England) and lactate
[Lactate, Randox, England] using an ILAB 650 (Instrumentation
Laboratory, Cheshire, United Kingdom).
Plasma Caffeine and Chlorogenic Acid analysis
Plasma caffeine were analysed externally (City Hospital,
Dudley, Birmingham) using a reversed-HPLC-UV method. The
sample preparation included: 200 mL of plasma were added to
100 mL internal standard (Proxyphylline, Sigma, United King-
dom) before mixing, heating and adding 500 mL of acetic acid.
Caffeine and Coffee on Exercise Performance
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The supernatant was the injected (5 mL) onto a Phenomenex
Prodigy 15064.60 mm 5 mOctadecyl Silane (ODS) column using
an auto sampler and detected at a UV of 273 nm. Caffeine
concentrations were quantified using one point calibration from a
calibrator that had previously been internally validated against a 9
point calibration curve (City Hospital, Dudley, Birmingham). With
each batch two QC (High and Low) were run, with reference to
the internal standard to account for any loses.
The caffeine content of coffee and decaffeinated coffee were
confirmed at the School of Sport and Exercise Sciences. In brief,
coffee and decaf coffee samples were prepared (identical to
preparation described above) and cooled before 5 mL of each
sample were injected onto a Phenomenex Luna 10 mC
18
(2)
column using an auto sampler (WPS 3000, Dionex, United
Kingdom). The mobile phase consisted of 0.1 M acetic acid in
water and 0.1 M acetic acid in acetonitrile. Caffeine concentra-
tions were quantified using a 10-point caffeine calibration curve in
water.
Coffee and Decaf coffee were analysed for chlorogenic acids.
The analysis was conducted externally (Eurofins Scientific, Italy)
using a reverse HPLC methodology at 325 nm (Water Symmetry
C18, 25064.6 mm, 5 mm) with external 5-QCA standards for
quantification on a 3 point calibration (10–250 mg/kg). The
mobile phase consisted of aqueous 0.5% formic acid and
acetonitrile.
Statistical Analysis
Data analysis was performed using SPSS for WINDOWS
software (version 17; SPSS Inc, Chicago, IL). Data are expressed
as means 6SEMs, unless otherwise stated. A repeated measure
ANOVA was used to assess differences in respiratory, substrate
metabolism, plasma metabolite and caffeine concentration as well
as time trial performance measurements during each trial. In order
to detect differences across time and between treatments a Fisher
protected least significant differences post hoc test was used
Significance was set at P,0.05.
Results
Steady State Exercise
Whole body respiratory measures, HR and RPE. The
selected workload of 50% Wmax during the SS (17167W)
resulted in similar oxygen uptake ( _
VVO
2) (2590679, 2595689,
2465679, 2522671 mL/min for CAF, COF, DECAF and PLA
respectively P = 0.278). As a result the relative exercise intensity
during the SS was similar throughout each trial (5862%, 5862%,
5561% and 5561% for CAF, COF, DECAF and PLA
respectively P = 0.337). Energy expended during SS was also
shown to be similar (1607649 KJ, 1611654 KJ, 1531650 KJ,
1565643) for CAF, COF, DECAF and PLA respectively
P = 0.248). In addition no significant difference was observed in
average HR during exercise (11964, 11964, 11964, 12065 bpm
for CAF, COF, DECAF and PLA respectively P = 0.281) or RPE
values (1060, 1060, 1160 and 1160 for CAF, COF, DECAF
and PLA respectively P = 0.091) during SS between trials.
Carbohydrate and Fat oxidation. Carbohydrate oxidation
rates during SS significantly reduced in all treatments across time
(P = 0.001). However there was no significant difference in
carbohydrate oxidation between each of the treatments
(Figure 1A P = 0.288). Similarly, fat oxidation rates significantly
increased during SS in all treatments (P = 0.001). No significant
difference in fat oxidation was observed between each of the
treatments (Figure 1B P = 0.445). Accordingly the contribution of
carbohydrate and fat to total energy expenditure during SS was
Table 1. Mean caffeine and chlorogenic acid (Total 5-QCA) concentration in each treatment beverage serving.
Treatment
beverage
Serving
Volume (ml)
Caffeine content
(mg/serving)
Total 5-CQA
(mg/serving) % of Total 5-CQA
CQA 5-CQA 4-CQA 5-FQA 4-FQA 3,5-diCQA 3,4-diCQA 4,5-diCQA 4,5-CFQA
CAF 600 394.467.0 - ---------
COF 600 394.467.0 393.367.3 21% 32% 22% 8% 7% 3% 2% 3% 2%
DECAF 600 13.460.2 328.166.1 23% 33% 24% 7% 7% 3% 1% 2% 1%
PLA600- - ---------
Abbreviations: CQA Caffeoylquinic acid, 5-CQA 5-O-Caffeoylquinic acid, 4-CQA 4-O-Caffeoylquinic acid, 5-FQA 5-O-Feruloylquinic acid, 4-FQA 4-O-Feruloylquinic acid, 3,5-diCQA 3,5-O-Dicaffeoylqui nic acid, 3,4-diCQA 3,4-O-
Dicaffeoylquinic acid, 4,5-diCQA 4,5-O-Dicaffeoylquinic acid, 4,5-CFQA 4,5-O-Dicaffeoylquinic acid, ml millilitres, mg milligrams, CAF Caffeine, COF Coffee, DECAF Decaffeinated Coffee, PLA Placebo.
doi:10.1371/journal.pone.0059561.t001
Caffeine and Coffee on Exercise Performance
PLOS ONE | www.plosone.org 4 April 2013 | Volume 8 | Issue 4 | e59561
not significantly different between any of the treatments
(P = 0.463).
Plasma metabolite concentrations. Plasma metabolite
responses at rest and exercise are displayed in Figure 2 A–D.
Plasma glucose concentrations (Figure 2A) were significantly
elevated at the end of rest compared to the beginning of rest
following CAF and COF (p,0.05 for both), while no significant
difference occurred following DECAF or PLA (P = 0.676 and
0.188 respectively). The elevation in glucose concentrations with
CAF following the rest period was significantly higher compared
to DECAF only (P,0.05). During exercise, plasma glucose
increased over time following CAF and COF, however only
COF reached statistical significance (P,0.05). DECAF and PLA
glucose concentrations fell during the onset of exercise with a
significant increase in both treatments later in exercise (T =10–30
P,0.05 for both). As a result, CAF had significantly higher glucose
concentrations within the first 20 minutes of exercise compared to
DECAF and PLA (P,0.05 for both), while at end of exercise CAF
and COF had significantly higher glucose concentrations com-
pared to PLA only (P,0.05 for both). Plasma FAs concentration
(Figure 2B) were significantly elevated at the end of rest compared
to beginning of rest following CAF (P = 0.010), while DECAF and
PLA had reduced FA concentration, with only DECAF reaching
statistical significance (P = 0.007 and P = 0.072 respectively).
Therefore, CAF had significantly higher FAs concentration
compared to DECAF and PLA at end of rest period (P,0.05
for both). During the beginning of exercise, CAF continued to
have significantly elevated FAs concentration compared to
DECAF only (P = 0.037). FA concentration significantly increased
during exercise (T = 10–30 P = 0.030) with no significant differ-
ences observed between treatments (P = 0.231).
Plasma glycerol concentrations (Figure 2C) did not significantly
change at rest for CAF (P = 0.066), COF (P = 0.392) and DECAF
(P = 0.104) but PLA significantly fell (P = 0.022). DECAF was
significantly lower at end of rest compared to CAF, COF and PLA
(P,0.05 for all), with no significant differences observed between
any other beverage. During exercise there was a significant
increase in glycerol concentrations for all treatments over time
(P = 0.001), with significantly higher concentrations observed for
CAF (P = 0.027) and COF (P = 0.003) at beginning of exercise
compared to DECAF only. Plasma lactate concentrations
(Figure 2D), were significantly increased following the consump-
tion of CAF and COF only during the rest period compared to
DECAF (P = 0.050 and P = 0.003 respectively) and PLA (P = 0.002
and P = 0.001 respectively). In addition DECAF had significantly
elevated lactate compared to PLA at end of rest period (P = 0.012).
All treatments lactate concentrations significantly increased at the
onset of exercise (P = 0.004) with CAF and COF being signifi-
cantly higher compared to PLA (P = 0.037 and P = 0.010
respectively). CAF and COF had sustained lactate concentrations
at the end of exercise, with significantly higher concentrations
compared to DECAF (P = 0.008 and P = 0.028 respectively) and
PLA (P = 0.050 and P = 0.005 respectively).
Plasma caffeine concentrations. The plasma caffeine
concentrations following each beverage are displayed in Figure 3.
At baseline plasma caffeine concentrations were very low for all
treatments (,3mM), with no significant differences observed
(P = 0.478). Plasma caffeine significantly increased following CAF
and COF when compared to DECAF (P = 0.000 and P = 0.009
respectively) and PLA (P = 0.000 and P = 0.010 respectively), with
peak concentrations observed 60 min after intake (38.262.8 mM
and 33.565.0 mM respectively). No significant difference was
observed in the plasma caffeine concentrations between CAF or
COF (P = 0.156) and DECAF or PLA (P = 0.558) throughout the
trials.
Time trial performance
CAF and COF significantly improved TT finishing times when
compared to both DECAF (P,0.05 for both) and PLA (P = 0.007
and P = 0.010) (Figure 4). As a result mean power output during
the TT was significantly greater for both CAF and COF compared
to DECAF and PLA (29466, 29167, 27667, 27764W,
respectively P,0.05 for both). However no significant differences
were seen in average heart rate during the TT between CAF,
COF, DECAF and PLA (17063, 16764, 16463, 16564 BPM,
respectively P = 0.516). CAF significantly improved TT perfor-
Figure 1. Carbohydrate oxidation (g/min) (A) and fat oxidation (g/min) (B) rates during 30 min steady state exercise (55% VO
2
max)
1 hour following ingestion of caffeine, coffee, decaf or placebo beverages. Data represented seen as Closed circles – Caffeine Open circles
– Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo. Means 6SE n = 8
doi:10.1371/journal.pone.0059561.g001
Caffeine and Coffee on Exercise Performance
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mance by 4.9% (95% confidence interval (CI) = 2.3–6.8%) and
4.5% (95% confidence interval (CI) = 2.3–6.2%) compared to PLA
and DECAF respectively (p,0.05 for both). Equally, COF
significantly improved TT performance by 4.7% (95% confidence
interval (CI) = 2.3–6.7%) and 4.3% (95% confidence interval
(CI) = 2.5–7.1%) compared to PLA and DECAF respectively
(p,0.05 for both) (Table 2). In addition there were no significant
differences in TT finishing time between CAF and COF
(P = 1.000) or PLA and DECAF (P = 1.000).
Following the completion of the TT, 3/8 participants were able
to successfully guess the correct order of test beverages consumed
prior to the trial. The correct guesses were more consistent for
detecting CAF compared to the other drinks, with 6/8 of the
participants guessing correctly. None of the participants reported
any serious symptoms of GI distress at the end of any of the trials.
Discussion
The present study examined the effects of acute intake of coffee
(5 mg CAF/kg BW) and caffeine (5 mg CAF/kg BW) on time trial
cycling performance, as well as substrate utilisation during SS
exercise. Numerous studies to date have shown the efficacy of
acute caffeine ingestion for improving prolonged endurance
exercise performance [1–7]. The effects of caffeine on time trial
endurance performance (.5 min) have recently been reviewed in
a well conducted meta-analysis [7]. The authors concluded that of
the 12 studies that investigated caffeine intake (1–6 mg CAF/kg
BW), performance was improved by ,3%. Fewer studies have
investigated the ergogenic effects of coffee, with results being
mixed thus far. In agreement with the literature, the current study
found an improvement in performance following caffeine intake of
4.9% and 4.5% when compared to decaf coffee and placebo,
respectively (Table 2). Interestingly, the current study also showed
that coffee improved performance to the same extent as caffeine
when compared to decaf coffee and placebo, 4.7% and 4.3%
respectively. Thus, this is the first study to date to demonstrate that
coffee consumed 1 h prior to exercise, at a high caffeine dose
(5 mg CAF/kg BW), is equally as effective as caffeine at improving
endurance exercise performance.
Our findings are in line with a number of studies that have
shown improvements to performance following coffee intake
[9,19–21]. Costill et al [9] were the first to show that decaf coffee
plus caffeine (330 mg), improved exercise time to exhaustion (80%
Figure 2. Plasma metabolite responses at rest (t = -60-0) and during 30 min steady state exercise (55% VO
2
max) (t = 0–30) following
ingestion of caffeine, coffee, decaf or placebo beverages. A Glucose. B Fatty acids (FA). C Glycerol. D Lactate. Data represented seen as Closed
circles – Caffeine Open circles – Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo. a Sig. different between CAF and
DECAF (p,0.05) b Sig. different between CAF and PLA (p,0.05) c Sig. different between COF and DECAF (p,0.05) d Sig. different between COF and
PLA (p,0.05). Means 6SE n = 7.
doi:10.1371/journal.pone.0059561.g002
Caffeine and Coffee on Exercise Performance
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Figure 3. Plasma caffeine concentrations following ingestion of caffeine, coffee, decaf or placebo beverages. a CAF significantly
different to DECAF and PLA (p,0.001) b COF significantly different to DECAF and PLA (p,0.05). Data represented seen as Closed circles – Caffeine
Open circles – Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo Means 6SE n = 7.
doi:10.1371/journal.pone.0059561.g003
Figure 4. Time trial finishing time (min) for caffeine, coffee, decaf or placebo beverages a CAF significantly different to DECAF and
PLA (p
,
0.05) b COF significantly different to DECAF and PLA (p
,
0.05). Data represented seen as Closed bar– Caffeine Open bar –
Caffeinated Coffee Dark grey bar– Decaffeinated coffee Light grey bar– Placebo. Means 6SE n = 8.
doi:10.1371/journal.pone.0059561.g004
Caffeine and Coffee on Exercise Performance
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VO
2
max) compared with decaffeinated coffee (,18%). More
recently, Wiles et al [19] showed that coffee was able to improve
1500 m treadmill running performance when compared to
decaffeinated coffee (,3%). However, the current study results
are in contrast to a number of other studies [22–24]. For example,
the work conducted by Graham et al [22] showed that coffee
(4.5 mg CAF/kg BW), regardless of the format of intake (regular
coffee or decaffeinated coffee plus caffeine) did not result in an
improvement to running time to exhaustion (75% VO
2
max),
where as caffeine (4.5 mg CAF/kg BW) significantly improved
performance. Therefore it was concluded by Graham et al [22]
that the performance effects of coffee may be inferior to caffeine.
Despite this evidence, the current study clearly demonstrates that
coffee is as effective as caffeine at improving endurance exercise
performance.
The discrepancy in the performance effects of caffeine and
coffee between the present study and Graham et al [22] might be
explained by the type of performance test implemented. Time to
exhaustion tests have been shown to be highly variable from day to
day, with a coefficient of variation (CV) ,27% in one study [18].
It is possible that this large variability may have contributed to the
lack of performance effects found by Graham et al [22]. Whereas
using a time trial performance measure, as used in the current
study, has previously been shown to be highly reproducible
(CV,3%) and could detect smaller differences in performance
[18]. Also the number of comparisons in the study by Graham et
al [22] was greater than in the present study with a similar subject
number, indicating that their statistical power was smaller.
Perhaps for these reasons, the current study was able to detect
similar changes in performance following caffeine and coffee
intake (,5%) (Table 2), whereas Graham et al [22] did not.
The composition and preparation of coffee in each of the studies
[9,19–24] may also explain the discrepancies in the ergogenic
effects of coffee. Coffee is ,2% caffeine, with the remainder
composed of chlorogenic acids, ferulic acid, caffeic acid, nicotinic
acid as well as other unidentifiable compounds [26]. It is evident
that the source of coffee beans, roasting, storage and preparation
(brewing and filtering) dramatically alters the caffeine and
chlorogenic acid content of the coffee [26]. In accordance, recent
evidence has shown that the chlorogenic acid content of
commercially available espresso coffees range from 24–422 mg/
serving [26]. In support, the current study observes a high
chlorogenic acid content in both coffee and decaffeinated coffee
samples (Table 1). Graham et al [22] speculated that chlorogenic
acids found in coffee may have blunted the physiological effects of
caffeine, preventing an improvement in exercise performance.
However the authors did not report measurements of chlorogenic
acids in coffee or in plasma to support this speculation. Despite the
compounds present in coffee, the authors reported that the
bioavailability of plasma caffeine and paraxanthines did not differ
to caffeine [22], which is in line with the present study (Figure 4).
Further, in vitro studies suggest that chlorogenic acids antagonize
adenosine receptor binding of caffeine [27] and cause blunting to
heart rate and blood pressure in rats [28]. Yet, in vivo there is no
evidence to suggest that chlorogenic acids, especially at the low
nanomolar concentration typically observed [32], impact on the
mechanisms of action of caffeine that lead to the ergogenic effects.
In support of this notion, and in agreement with the current study,
regular coffee (1.1 mg/kg/BW) consumed prior to the ingestion of
different doses of caffeine (3–7 mg/kg/BW) has been shown not to
affect the ergogenic effects of caffeine [21].
The improvement in performance in the current study is
unlikely to be explained by alterations to fat oxidation, as no
difference during the SS exercise bout was observed (Figure 1B).
This is in agreement with a number of investigations that do not
support the thesis that caffeine improves exercise performance by
augmenting fat metabolism [33,34]. In addition these effects are
apparent despite consistent increases in adrenaline though
activation of the SNS [33,34] and a subsequent elevation in FA
appearance in the circulation following caffeine intake [33,34]. It
is evident that the improvement in performance is likely through
caffeine’s direct antagonism of adenosine receptors (A
1
and A
2A
)on
the skeletal muscle membrane to improve excitation-contraction
coupling [13] via a greater release of Ca
2+
from the SR [16] and/
or improved Na
+
/K
+
ATPase pump activity [15]. In support of
this notion, Mohr et al [12] observed that tetrapelegic patients,
who have an impaired sympathoadrenal response [35], showed
that caffeine improved exercise performance, while RER did not
change during an electrical stimulated cycling test. Further, the
authors also observed a significant increase in FA and glycerol at
rest and during exercise following caffeine intake, despite a lack of
an adrenaline response. This is due to the fact that adenosine has
been shown to inhibit lipolysis [36] and enhance insulin stimulated
glucose uptake in contracting skeletal muscle in vitro [37]. In
support, the current studyobserved a significant increase in plasma
glucose, FA and glycerol concentrations following caffeine
(Figure 2 A, B, C). In addition, the consistently reported elevation
in adrenaline concentrations [33] combined with adenosine
receptor antagonism following caffeine intake during exercise
may work synergistically to activate glycogenolysis in exercising
and non-exercising tissues [34] as well as adipose tissue/skeletal
muscle lipolysis [33]. This supports the fact that the current study
(Figure 2 D) and others have shown that caffeine increase plasma
lactate concentrations at rest and during exercise [33,34]. Though
to date there is little supporting evidence that caffeine stimulates
exercising skeletal muscle glycogenolysis [33,38], with early studies
showing a paradoxical glycogen sparing effect with caffeine [2].
The elevated lactate concentrations are more likely due to a
Table 2. Time trial performance data for each treatment.
Treatment TT finish time (min)
Improvement compared to
PLA % (95% confidence
intervals) P value
Improvement compared to DECAF
% (95% confidence intervals) P value
CAF 38.3560.48
a
4.9 (2.326.8) 0.007 4.5 (2.326.2) 0.012
COF 38.2760.57
b
4.7 (2.326.7) 0.010 4.3 (2.527.1) 0.012
DECAF 40.2360.63 20.4 (24.023.1) 1.000 - -
PLA 40.0660.39 - - 0.3(20.323.9) 1.000
Means 6SE n = 8 a significantly different to DECAF and PLA (p,0.05) b significantly different to DECAF and PLA (p,0.05) Abbreviations: CAF Caffeine, COF Coffee,
DECAF Decaffeinated Coffee, PLA Placebo.
doi:10.1371/journal.pone.0059561.t002
Caffeine and Coffee on Exercise Performance
PLOS ONE | www.plosone.org 8 April 2013 | Volume 8 | Issue 4 | e59561
reduced clearance by the exercising muscle and a greater release
by non exercising tissues [33]. Consequently, due to the healthy
participants tested in the current study it is likely that the
adenosine receptor antagonism by caffeine plays a crucial role in
inducing the ergogenic effects of caffeine while regulating the
metabolite response synergistically with the SNS.
Interestingly, despite coffee producing similar ergogenic effects
as caffeine, the metabolite responses were not identical (Figure 2).
The current study observed that the significant increase in plasma
glucose, FA and glycerol with caffeine was paralleled with an
attenuated response for coffee, and a significantly blunted response
with decaf coffee when compared to placebo (Figure 2 A, B, C).
This is likely due to the compounds in coffee [39] inducing subtle
effects on antagonism of adenosine receptors (A
1
and A
2A
)ina
variety of exercising and non exercising tissues. In accordance,
Graham et al [22] previously showed that coffee resulted in a
blunted adrenaline response when compared to caffeine at rest in
humans, which was attributed to chlorogenic acids antagonizing
adenosine receptor binding of caffeine [27]. In addition nicotinic
acid, a fatty acid ester found in coffee known to inhibit lipolysis,
has been shown to lower FA concentrations in patients suffering
from hyperlipidemia [40]. Chlorogenic acids are also believed to
improve glucose uptake at the skeletal muscle when compared to
caffeine [41], also by altering the antagonism of adenosine
receptors. More recently, caffeic acid has been found to stimulate
skeletal muscle glucose transport, independent of insulin, when
accompanied with an elevation in AMPK in vitro [42]. Despite the
aforementioned evidence, it remains unclear why compounds in
coffee appear to modulate the metabolite response but not the
ergogenic effects of coffee in the current study.
The current study provided a large bolus of caffeine in the form
of anhydrous caffeine or coffee one hour prior to exercise (5 mg/
kg BW). The chlorogenic acid content of the coffee beverages was
different, which is worth highlighting as a potential limitation of
the current study. Previous studies have failed to make compar-
isons between coffee and decaf coffee and instead have used decaf
plus anhydrous caffeine [9,19-21,23,43]. In addition these studies
did not examine the chlorogenic acid content of the test beverages.
Thus, the novelty of the current study was that the performance
effects were investigated between caffeine and coffee, independent
of the combined effects of decaffeinated coffee plus caffeine.
Adding a decaf plus caffeine trial would have been successful in
controlling for chlorogenic acid content of the beverage. However,
firstly, investigating the effect of chlorogenic acids on the metabolic
and performance effects of caffeine was not the primary aim of the
current study. Secondly, and more importantly, the low nanomo-
lar concentration of chlorogenic acids in vivo [32] is unlikely to
impact on the mechanisms of action of caffeine when compared to
the physiological effects observed in vitro from supra physiological
concentrations of chlorogenic acids [27,28]. Yet, as differences in
the metabolic effects of caffeine compared to coffee were observed
in the current study, it may be important for future studies to
control for chlorogenic acid content in coffee beverages or
additionally increase the dose of chlorogenic acids to raise the
bioavailability in vivo. In turn this will provide further insights into
the metabolic differences between caffeine and coffee. In
conclusion, the present study showed that caffeine and coffee
(5 mg CAF/kg BW) were both able to improve exercise
performance to the same extent, when compared to both
decaffeinated coffee and placebo. Our data does not support the
notion that chlorogenic acids found in coffee impair the ergogenic
effects of caffeine. However, the compounds found in coffee may
alter the metabolic effects, as the current study observed
differences between caffeine and coffee at rest and during exercise.
It is yet to be determined if lower doses of caffeine, when ingested
as coffee, offer the same ergogenic effects. This would offer a more
applicable and realistic nutritional strategy for athletes.
Acknowledgments
The authors express appreciation to Dr Gareth Wallis for his input and
advice in the preparation of this paper.
Author Contributions
Critically reviewed the paper: ABH RKR AEJ. Conceived and designed
the experiments: ABH RKR AEJ. Performed the experiments: ABH RKR.
Analyzed the data: ABH AEJ. Wrote the paper: ABH AEJ.
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