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Contents lists available at ScienceDirect

Journal of Science and Medicine in Sport

j our na l ho me page: www.elsev ier .com/ locate / j sams

riginal research

ffect of caffeine on cycling time-trial performance in the heat

athan W. Pitchforda, James W. Fell a, Michael D. Leverittb,c,en Desbrowb, Cecilia M. Shinga,∗

Sport Performance Optimisation Research Team, School of Human Life Sciences, University of Tasmania, AustraliaSchool of Public Health, Griffith University, AustraliaSchool of Human Movement Studies, The University of Queensland, Australia

a r t i c l e i n f o

rticle history:eceived 19 February 2013eceived in revised form 30 June 2013ccepted 10 July 2013vailable online xxx

eywords:,3,7-Trimethylxanthineeataffeine

a b s t r a c t

Objectives: The purpose of this investigation was to determine whether a moderate dose of caffeine wouldimprove a laboratory simulated cycling time-trial in the heat.Methods: Nine well-trained male subjects (VO2max 64.4 ± 6.8 mL min−1 kg−1, peak power output378 ± 40 W) completed one familiarisation and two experimental laboratory simulated cycling time-trials in environmental conditions of 35 ◦C and 25% RH 90 min after consuming either caffeine (3 mg kg−1

BW) or placebo, in a double blind, cross-over study.Results: Time-trial performance was faster in the caffeine trial compared with the placebo trial(mean ± SD, 3806 ± 359 s versus 4079 ± 333 s, p = 0.06, 90%CI 42–500 s, 86% likelihood of benefit,d = −0.79). Caffeine ingestion was associated with small to moderate increases in average heart rate

ore temperatureycling

(p = 0.178, d = 0.39), VO2 (p = 0.154, d = 0.45), respiratory exchange ratio (p = 0.292, d = 0.35) and core tem-perature (p = 0.616, d = 0.22) when compared to placebo, however, these were not statistically significant.Average RPE during the caffeine supplemented time-trial was not significantly different from placebo(p = 0.41, d = −0.13).Conclusion: Caffeine supplementation at 3 mg kg−1 BW resulted in a worthwhile improvement in cyclingtime-trial performance in the heat.

201

©

. Introduction

Caffeine (1,3,7-trimethylxanthine) is one of the most popu-ar and accepted ergogenic aids used by athletes in enduranceports.1–3 It has well-documented positive effects on exercise per-ormance in standard ambient temperatures (∼21 ◦C and 40% RH)articularly in exercise tasks which last 30 min or longer.4 How-ver, the ergogenic benefits of caffeine consumed before exercisen the heat are much less convincing.5–7 Del Coso et al.7 havehown that caffeine can enhance quadriceps force production after20 min of cycling in the heat. Conversely, caffeine consumed atoses of 6 and 9 mg kg−1 BW before cycling time-trials in theeat does not appear to enhance performance,5,8 nor was there an

mprovement in 21 km run time in warm field conditions when 5r 9 mg kg−1 BW of caffeine was consumed before exercise.6 Takenogether, these studies suggest that caffeine may not be ergogenic

Please cite this article in press as: Pitchford NW, et al. Effect of caffeine ohttp://dx.doi.org/10.1016/j.jsams.2013.07.004

hen consumed before exercise performed in the heat.Although caffeine has well-noted beneficial effects on

ndurance performance, heat has been shown to have detrimental

∗ Corresponding author.E-mail address: cecilia.shing@utas.edu.au (C.M. Shing).

440-2440/$ – see front matter © 2013 Sports Medicine Australia. Published by Elsevier Lttp://dx.doi.org/10.1016/j.jsams.2013.07.004

3 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

effects on endurance performance,9–11 even in heat adaptedindividuals.10 Heat increases core temperature11 and this isthought to be the main limiting factor on endurance performanceas increased core temperature increases the thermoregulatorystress placed on the body to maintain a stable internal environmentand may lead to reductions in central drive, limiting enduranceperformance.11 Exercise in the heat and the increased reliance onevaporative heat loss mechanisms increase core temperature,10

sweat rate,9 heat transfer from the skin9,12 and potentially reducecentral drive to continue exercise.13 Increased sweat rate duringexercise in the heat leads to increased fluid loss and reduced bloodvolume, which has a cascade effect in reducing stroke volume,increasing heart rate and limiting endurance capacity. There isevidence to suggest that caffeine supplementation is associatedwith increased core temperature, heart rate and sweat rate whencompared to a placebo at a set work rate.5,14,15 Thus plausiblereasons for any lack of benefit from high dose caffeine under hotconditions may be due to some of the metabolic effects associatedwith caffeine such as increased core temperature8 due to increased

n cycling time-trial performance in the heat. J Sci Med Sport (2013),

work output, or by affecting diuresis or sweat rate.15,16 Caffeinesupplementation has, in some cases, been shown to cause a greaterrise in core temperature during steady-state endurance exercisein a hot environment compared with a placebo,8,16 while other

td. All rights reserved.

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tudies show only very subtle perturbations in body temperaturend heat storage resulting from caffeine ingestion prior to exercisen the heat.7,17 Nevertheless, it is possible that when exercise iserformed in a hot environment, the ergogenic effects of caffeinere negated due to elevations in physiological variables such asody temperature, heart rate and sweat rate.5,8

Interestingly, the studies showing no improvement in exerciseerformance in the heat after caffeine ingestion have used rela-ively high doses ranging from 5 to 9 mg kg−1 BW.5,6,8 The ergogenicffects of caffeine on endurance time-trial performance in ambientonditions appear to plateau at doses close to 3 mg kg−1 BW witho additional benefit from higher doses.14,18 The effect of a mod-rate dose (∼3 mg kg−1 BW) of caffeine on exercise performance inhe heat is yet to be investigated.

The purpose of this investigation was to determine the effect of 3 mg kg−1 BW dose of caffeine on cycle time-trial performancen the heat. It was hypothesised that a 3 mg kg−1 BW dose of caf-eine would enhance performance to a similar extent to what hasreviously been observed during exercise in standard laboratoryemperatures.14

. Methods

Participants were nine highly trained male cyclists (22–42ears, body mass 73.56 ± 8.28 kg, height 176.6 ± 8.7 cm, VO2max4.4 ± 6.8 mL min−1 kg−1 and peak power output 378 ± 40 W).even of the nine participants were regular caffeine consumersn the average range of 100–300 mg day−1. The research was con-ucted according to the National Statement on Ethical Conduct

n Human Research (2007) (Australia) and was approved by theasmanian Human Research Ethics Committee (approval number11654). Participants were recruited from cycling clubs aroundorthern Tasmania and were required to have a minimum of twoears cycling experience.

The study was a randomised, counterbalanced, double-blind,lacebo-controlled, cross-over design. Cyclists attended the labora-ory on four separate occasions including two experimental trials.he first visit involved measurement of VO2max and peak powerutput in laboratory conditions of 21 ◦C and 40% relative humid-ty (RH). The second visit was a familiarisation session where theycling time-trial was completed in hot conditions (35 ◦C and 25%H) without respiratory measurements or blood sampling. The twoxperimental trials involved cyclists ingesting either 3 mg kg−1 ofW anhydrous caffeine (PCCA, NSW, Australia) or an equivalentmount of placebo (MetamucilTM, NSW, Australia) 90 min beforeompleting the cycling time-trial in the climate chamber.

Participants’ VO2max and peak power (Wmax) were determinedsing an incremental test to exhaustion on a calibrated cyclergometer (Lode Excalibur Sport Cycle Ergometer, Groningen, Theetherlands). Participants began cycling at 100 W for 5 min with

ncreases in intensity of 50 W every 2.5 min until exhaustion, as pre-iously described by Desbrow et al.19 During the VO2max testingxpired air was collected and analysed using a calibrated metabolicart (ParvoMedics’ TrueOne2400). Heart rate (HR) was recordedvery 30 s of the test using a heart rate monitor (RS800CX, Polarnstruments Inc., Finland). Rating of perceived exertion (RPE) wasecorded at every stage of the test using Borg’s 6–20 RPE scale.20

O2max was determined as an average of the two highest 30 sonsecutive readings.

Each participant completed one familiarisation of the cyclingime-trial in the hot conditions, following the same protocol as the

Please cite this article in press as: Pitchford NW, et al. Effect of caffeine ohttp://dx.doi.org/10.1016/j.jsams.2013.07.004

uture exercise trials, with the absence of blood sampling and respi-atory gas collection. The cycle ergometer was adjusted to cyclists’ersonal specifications. Seat and bar height and positions were thenecorded and replicated in the subsequent exercise trials.

PRESSMedicine in Sport xxx (2013) xxx– xxx

Two experimental trials involving the consumption of either ananhydrous caffeine capsule (3 mg kg−1 BW) or a placebo capsulecontaining psyllium husk (Metamucil TM P&G Australia Pty Ltd.,Sydney, NSW, Australia) 90 min prior to exercise were completedby each participant. All exercise trials were completed at the sametime of day (morning) with at least seven days separating each trial.The climate chamber was set at 35 ◦C and 25% RH.

Prior to each trial, participants were asked to perform no phys-ical activity, aside from activities of daily living, for 24 h before thestart of each testing session and were provided with a 24 h pre-packaged diet including all food and fluid to be consumed beforethe trial and a standardised breakfast on the morning of each trial.The standardised diet was designed to minimise dietary differencesacross participants and between trials to ensure reliability, repro-ducibility and validity of time-trial results.21 The pre-packaged dietprovided 200 kJ kg−1 BW and 7.5 g kg−1 BW of carbohydrate for theday preceding the time-trials 40 kJ kg−1 BW and 1.5 g kg−1 BW ofcarbohydrate in the breakfast on the morning of time-trials. Partic-ipants were required to avoid alcohol for at least 24 h and caffeinefor at least 12 h prior to each trial.

Each exercise trial involved participants completing a time-trialon the same calibrated cycle ergometer. The protocol used was sim-ilar to that described by Irwin et al.22 However, the target amountof work was reduced by 20% to ensure that most participants com-pleted the time-trial in approximately 60 min in the hot conditions.The target amount of work was calculated according to the formula:

Total work (J) = 0.75 × PPO × 2880

The time-trial was performed with the ergometer set in lin-ear mode. The participants’ linear factors were determined on anindividual basis (during VO2max testing) to allow cycling at eachparticipant’s preferred cadence. Participants were required to per-form the set amount of work as fast as possible.

Throughout the two exercise trials VO2 was recorded at 25%,50%, 75% and 90% of time-trial completion (for 90 s with readingstaken every 15 s and the final three readings averaged) while ratingof perceived exertion (RPE) was recorded at 25%, 50%, 75%, 90%and 100% of time-trial completion. Core temperature was measuredcontinuously throughout the time-trials using Vitalsense (PhilipsRespironics, Eindhoven, Netherlands) core temperature capsulesingested 4 h prior to the onset of the exercise bout. Heart rate wasmonitored every 15 s throughout (RS800CX, Polar Instruments Inc.,Finland). Participants consumed 3 mL kg−1BW of a carbohydrateelectrolyte beverage (Gatorade) every 25% of time-trial completion,provided immediately after VO2 measurement. On completion ofthe study cyclists were asked to identify which trial they believedthey consumed caffeine pre-exercise.

Blood samples were obtained from the forearm antecubitalspace of each cyclist 90 min prior to exercise, 5 min pre-exerciseand immediately post-exercise for analysis of plasma caffeineconcentration. Blood was transferred into lithium heparin col-lection tubes then centrifuged at 4 ◦C for 15 min at 2500 rpm.Plasma was then extracted and stored at −80 ◦C until subse-quent analysis. The quantitative analysis of plasma caffeine wasperformed using an automated reversed-phase high-performanceliquid chromatography system, with conditions adapted with sub-tle modifications from Koch et al.23 The precise method has beenpreviously described by Desbrow et al.19

Before analysis, data was tested for normality using aKolmogorov–Smirnov test. All data were normally distributed with

n cycling time-trial performance in the heat. J Sci Med Sport (2013),

the exception of HR data expressed at 0%, 25%, 50%, 75%, 90% and100% time-trial completion which was then log transformed priorto analysis. To determine changes in cycling time-trial time andthe trial average of physiological variables a t-test was used while

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n analysis of variance was conducted to determine changes inhysiological variables during the trial (time) in each treatmentondition (caffeine versus placebo). To determine changes in bio-hemical variables in response to treatment condition a 2 (caffeineersus placebo) × 3 (pre-ingestion, pre-exercise and post-exercise)nalysis of variance was conducted. Significance was accepted at

< 0.05 and data are presented as mean ± SD. Cohen’s d was cal-ulated from trial averages (caffeine minus placebo, divided byooled standard deviation) and the effect size was interpreteds small = 0.2, moderate = 0.5 and large = 0.8.24 Magnitude basednferences were also employed to assess the practical effect of caf-eine on cycling time-trial performance. A sport science specific

icrosoft Excel spreadsheet was used25 to estimate the likelihoodhat the caffeine treatment would be beneficial, trivial or nega-ive to performance based upon the smallest worthwhile change.he smallest worthwhile change was deemed to be 3% (averagemprovement in time-trial performance following caffeine).4

. Results

Plasma caffeine significantly increased from 90 min pre-exerciseo 5 min pre-exercise (0.0 ± 0.0 �M–26.1 ± 5.5 �M; p < 0.0001) inhe caffeine group with no significant change in the placebo group,ith levels staying below the detectable limits. Post-exercise

Please cite this article in press as: Pitchford NW, et al. Effect of caffeine ohttp://dx.doi.org/10.1016/j.jsams.2013.07.004

affeine concentration was 26.7 ± 5.0 �M in the caffeine supple-ented trial and below the detectable limits in the placebo trial.

ive participants correctly identified the trial they consumed caf-eine pre-exercise.

ig. 2. Time-trial cumulative time-to-completion (A), heart rate (bpm) (B), core temperatime following supplementation with either caffeine (CAF) or placebo (PLA). Data are melacebo effect size.

Fig. 1. Time-trial time following supplementation with either caffeine (CAF) orplacebo (PLA) for each individual cyclist.

There was a moderate reduction (d = −0.79) in time-trial time-to-completion with caffeine (3806 ± 359 s) compared to placebo(4079 ± 333 s) (p = 0.06, Fig. 1). While this was not statisticallysignificant using two-way ANOVA analysis, when assessed usingmagnitude based inferences the ingestion of caffeine representedan 85.8% likely to be beneficial chance of improving time-trialperformance by 3% (90%CI 42 to 500 s), with a very unlikelychance of harm (0.6%), and a 13.6% chance that the effect wastrivial, compared to placebo. While 0–25% split time was similar

n cycling time-trial performance in the heat. J Sci Med Sport (2013),

between trials (d = −0.11), caffeine was associated with small tovery large reductions in split times at 25–50%, 50–75%, 75–90% and90–100% completion, however, these were not significantly differ-ent compared to placebo (p = 0.149, −0.26, −0.44, −1.13 and −0.73,

ure (C), RER (D), VO2 (E) and RPE (F) at 0%, 25%, 50%, 75%, 90% and 100% of time-trialan ± SD with Cohen’s d presented above each time point representing the caffeine

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Table 1Average heart rate (HR), rating of perceived exertion (RPE), core temperature (coretemp.), respiratory exchange ratio (RER) and VO2 for time-trial.

Variable Placebo Caffeine p value d

HR (bpm) 168 ± 10 171 ± 7 0.18 0.39RPE 16.9 ± 1.3 16.8 ± 1.1 0.41 −0.13Core temp. (◦C) 39.0 ± 0.5 39.1 ± 0.3 0.62 0.22RER 0.93 ± 0.03 0.95 ± 0.05 0.29 0.35

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VO2 (ml kg min−1) 38.2 ± 3.1 39.6 ± 3.2 0.15 0.45

alues are mean ± SD. d = effect size.

espectively) (Fig. 2). There were small to moderate increasesn average heart rate, VO2, respiratory exchange ratio (RER) andore temperature during the caffeine trial, when compared to thelacebo, however, these were not statistically significant (Table 1).hile there was no significant interaction of treatment condi-

ion × time for HR (p = 0.736), VO2 (p = 0.915), RER (p = 0.945), coreemperature (p = 0.66) or RPE (p = 0.534), caffeine was associatedith small to moderate increases in HR, RER, VO2 and core temper-

ture and a large reduction in RPE at 25% of time trial completionFig. 2). Fig. 2 presents the cumulative time trial splits and aver-ge physiological variables at each split under caffeine and placeboonditions.

Pre-exercise body weight was not significantly differ-nt (p = 0.33) between caffeine (74.32 ± 7.06 kg) and placebo74.11 ± 6.97 kg) trials. Body weight was significantly reducedre- to post-exercise in both trials (caffeine: −1.49 ± 0.32 kg andlacebo: −1.53 ± 0.31 kg; p < 0.0001); however, there was noignificant difference in weight loss between treatments (p = 0.42,

= −0.11).

. Discussion

The purpose of this investigation was to determine the effect of moderate dose of anhydrous caffeine on cycling performance inhe heat. A 3 mg kg−1 BW dose of caffeine consumed 90 min prior toxercise improved cycling time-trial performance in 35 ◦C and 25%H, with an 85.8% likelihood of benefit and a very unlikely chance ofarm (0.6%). Moderate dose caffeine consumed before endurancexercise in the heat appears to be ergogenic for cycling time-trialerformance.

While caffeine is ergogenic in standard laboratory condi-ions, supplementation in a hot environment may negate thergogenic effects due to increased temperature and cardiovascu-ar strain.5,8 However, our findings suggest that moderate doseaffeine (3 mg kg−1) improves cycling time-trial performance (86%ikelihood of benefit) in the heat in trained, non-acclimated cyclists.n contrast, some studies that have employed a higher caffeineose have reported no clear ergogenic effect of caffeine in theeat.6,8,26 Roelands et al.8 suggested that a higher core temperaturefter 6 mg kg−1 caffeine supplementation negated any potentialrgogenic benefits. In the present study core temperature wasot significantly higher during the caffeine trial and it may behat higher caffeine doses influence core temperature to a greaterxtent. While a study by Cohen et al.6 did not report higherore temperatures with a 5 mg kg−1 and 9 mg kg−1 dose of caf-eine, core temperature was assessed using tympanic membraneemperatures and these have been shown to be unsuitable forssessing hyperthermia during exercise.27 Interestingly, work byanio et al.26 concluded that caffeine was beneficial to cycling per-

ormance across both ambient and hot conditions but they didot provide a direct comparison between caffeine and placebo for

Please cite this article in press as: Pitchford NW, et al. Effect of caffeine ohttp://dx.doi.org/10.1016/j.jsams.2013.07.004

he hot (33 ◦C) condition only. When magnitude based inferencesre calculated from this manuscript for the hot condition (using

worthwhile performance improvement of half the between sub-ect standard deviation), compared to a placebo, caffeine was 73.3%

PRESSMedicine in Sport xxx (2013) xxx– xxx

likely to increase total work done in a 15 min time-trial performedafter 90 min of endurance cycling, with a very unlikely chance ofharm (0.5%) (p = 0.082). This apparent ergogenic effect of caffeineoccurred without a significant increase in rectal temperature andthis contrast to the study of Roelands et al., 8 may have been due tothe dosage protocol employed whereby a 3 mg kg−1 dose of caffeinewas ingested 1 h prior to and again at 45 min into the 90 min cyclingin 33 ◦C. While still an absolute 6 mg kg−1 dose in the study by Ganioet al.,26 which may have limited the ergogenic effect of caffeine,the splitting of the dose may also have distributed any thermo-genic effect. In contrast, a 6 mg kg−1dose taken 1 h prior to a 60 minconstant load cycle followed by a time-trial in 30 ◦C significantlyraised core temperature throughout the exercise and there wasno significant time-trial performance improvements attributableto the caffeine (p = 0.46, likely 100% trivial for benefiting exerciseperformance).8 Consequently, lower doses or distributing the dosesmay provide a better way to administer caffeine for exercise in hotconditions.

Caffeine induced diuresis, increased sweat rate and onset ofsweating during exercise are also suggested as some of the detri-mental effects of caffeine consumption that might affect exerciseperformance.16 Recently, Kim et al.16 found increased sweat ratesand reductions in onset of sweating time during 30 min of submax-imal exercise in the heat following 3 mg kg−1 BW caffeine. This isinconsistent with earlier literature which has shown that caffeinedoes not influence fluid loss and sweat rates during exercise in bothstandard laboratory conditions18 or hot environments.15 Cyclistsin the present study ingested the same amount of fluid and hadthe same body weight losses between trials, suggesting that caf-feine did not increase sweat rate. Indeed, dehydration in the rangereported in the current study (<2%) is unlikely to impair enduranceperformance.28

Cyclists in the current study had a small to moderate increase inHR, RER, VO2 and core temp during the caffeine trial. While not sta-tistically significant these may reflect increased exercise intensity,and hence the moderate to large improvement in time to completethe set amount of work (d = −0.79). Despite the increased exer-cise intensity mean RPE during the caffeine trial was not higher(d = −0.13). In standard laboratory conditions, fixed work rates areassociated with lower RPE following the ingestion of caffeine whencompared to a placebo.29 In support of caffeine reducing perceivedexertion Astorino et al.30 reported that cyclists completed a time-trial in a hot environment faster with caffeine supplementationcompared to a placebo, despite a similar RPE. The present study sup-ports that caffeine may indeed dampen the perception of increasedexercise intensity, leading to improved performance. It is importantto note that a limitation of caffeine research is difficulty in blindingparticipants to caffeine ingestion and five of the nine cyclists in thisstudy correctly identified the caffeine trial.

5. Conclusion

Caffeine at a dose of 3 mg kg−1 BW 90 min prior to exercise inthe heat may benefit endurance athletes that are not acclimated tohot (35 ◦C, 40% humidity) conditions as it produces a worthwhileimprovement in one hour time-trial performance in the heat. Mod-erate dose caffeine that enhances endurance cycling performancein standard laboratory conditions14 is also ergogenic in the heat.

6. Practical applications

n cycling time-trial performance in the heat. J Sci Med Sport (2013),

• Caffeine could be considered an ergogenic aid for non-heatacclimated, hydrated endurance athletes competing in hot envi-ronments (35 ◦C, 40% humidity).

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Supplementing with 3 mg kg−1 BW of caffeine 90 min prior toendurance cycling in the heat is associated with a worthwhileimprovement in one-hour time-trial performance.A moderate dose of caffeine does not enhance fluid (body weight)loss during exercise in the heat.

cknowledgements

The authors have no conflicts of interest to declare. There was nonancial assistance received for this project. We thank the cyclists

or their dedication and enthusiasm throughout their involvementn the present study.

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