ARTICLE

Caffeine, but not bicarbonate, improves 6 min maximalperformance in elite rowers1

Peter M. Christensen, Mads H. Petersen, Signe N. Friis, and Jens Bangsbo

Abstract: This study examined the ergogenic effects in a 6 min maximal performance test (PT) on 12 elite rowers: 6 open-weight(mean ± SD; 25 ± 1 years, and 92 ± 3 kg) and 6 light-weight (25 ± 3 years, and 73 ± 6 kg), following supplementation with caffeine(CAF), sodium bicarbonate (SB), and the combination of both, in a double-blind randomized placebo (PLA) controlled design. PTwas executed on 4 occasions, on separate days within a week, and in a non-fasted state, with standardized training beingperformed the day before PT. Protocols were as follows: (i) CAF, 3 mg/kg, 45 min prior to PT + calcium as SB-PLA; (ii) SB, 0.3 g/kg,75 min prior to PT + dextrose as CAF-PLA; (iii) CAF + SB; and (iv) PLA; CAF-PLA + SB-PLA. The total distance in the CAF (1878 ± 97 m)and CAF + SB (1877 ± 97 m) was longer than in the PLA (1865 ± 104 m; P < 0.05) and SB (1860 ± 96 m; P < 0.01). The mean power inCAF (400 ± 58 W) and CAF + SB (400 ± 58 W) was higher than the PLA (393 ± 61 W; P < 0.05) and SB (389 ± 57 W; P < 0.01). In CAFand CAF + SB, power was higher (P < 0.05) relative to PLA in the last half (4–6 min) of PT. Trials with CAF were more effective inlight-weight rowers (1.0% ± 0.8% improvement in distance; P < 0.05) than in open-weight rowers (0.3% ± 0.8%; P > 0.05). Nodifference between interventions was observed for readiness and stomach comfort before PT and perceived exertion during PT.This study demonstrates that caffeine ingestion does improve performance in elite rowing. In contrast sodium bicarbonate doesnot appear to be ergogenic, but it does not abolish the ergogenic effect of caffeine.

Key words: caffeine, bicarbonate, buffer capacity, rowing, ergogenic aids, elite athletes, pacing.

Résumé : La présente étude examine l'effet ergogène de la supplémentation en caféine (CAF), en bicarbonate de sodium (SB) etdes deux substances dans un test de performance (PT) d'une durée de 6 min chez 6 rameurs d'élite de catégorie ouverte (25 ± 1 ans(moyenne ± é-t) et 92 ± 3 kg) et de poids léger (25 ± 3 ans et 73 ± 6 kg). Selon un plan aléatoire croisé avec groupe placebo (PLA),le PT est administré en 4 jours différents d'une même semaine dans une condition non a jeun et l'entraînement régulier esteffectué le jour précédant le PT. Les protocoles sont : (i) CAF, 3 mg/kg, 45 min avant PT + calcium a titre de SB-PLA; (ii) SB, 0,3 g/kg,75 min avant PT + dextrose a titre de CAF-PLA; (iii) CAF + SB; et (iv) PLA, CAF-PLA + SB-PLA. La distance totale dans les conditionsCAF (1878 ± 97 m) et CAF + SB (1877 ± 97 m) sont plus longues que dans les conditions PLA (1865 ± 104 m; P < 0,05) et SB (1860 ±96 m; P < 0,01). La puissance moyenne dans les conditions CAF (400 ± 58 W) et CAF + SB (400 ± 58 W) est plus élevée que dans lesconditions PLA (393 ± 61 W; P < 0,05) et SB (389 ± 57 W; P < 0,01). Dans les conditions CAF et CAF + SB, la puissance est plus élevée(P < 0,05) comparativement a la condition PLA durant la deuxième moitié (4–6 min) du PT. Les essais réalisés dans la conditionCAF donnent de meilleurs résultats chez les rameurs de poids léger (amélioration de la distance de 1,0 ± 0,8 %; P < 0,05) que chezles rameurs de catégorie ouverte (0,3 ± 0,8 %; P > 0,05). On n'observe pas de différence de l'état de préparation et des sensationsgastriques entre les diverses interventions avant le PT et de la perception de l'intensité de l'effort durant le PT. La présente étudedémontre l'efficacité de la caféine dans l'amélioration de la performance chez des rameurs d'élite. En revanche, le bicarbonatede sodium ne semble pas présenter un effet ergogène, mais n'annule pas l'effet ergogène de la caféine. [Traduit par la Rédaction]

Mots-clés : caféine, bicarbonate, capacité de tamponnage, aviron, facteurs ergogènes, athlètes d'élite, cadence.

IntroductionIn world-class rowing, the competition is performed over a

2000 m distance lasting �6 min. Often the difference between thewinners of medals is small. Thus, in 6 of the 8 finals in mensrowing at the London 2012 Olympics less than 2 s separated thegold medal winners from the silver. It is, therefore, essential toknow which substances can improve performance, and also toavoid the use of substances that have no effect on performanceand may cause unwanted side effects such as headache, stomachache, etc.

Caffeine (Burke 2008) and sodium bicarbonate (Carr et al. 2011b)are 2 substances that have been investigated in numerous studies

for their ergogenic potential in high intensity endurance sports(3–8 min). Caffeine appears to affect the central nervous system byaltering the perception of pain and motivation through actions onadenosine receptors (Tarnopolsky 2008; Meeusen et al. 2013).Moreover, caffeine increases adrenaline release and muscle lac-tate production (Jackman et al. 1996) and improves muscle potas-sium transport capacity (Mohr et al. 2011). In isolated animalmuscle fibres, caffeine in supraphysiological doses (5 mmol/L) isalso reported to potentiate force production via effects on calciumrelease (Allen and Westerblad 1995; Rosser et al. 2009). In contrast,a lower dose (70 �mol/L) is reported to have no effect on musclefunction (Rosser et al. 2009), with the latter concentration being

Received 14 December 2013. Accepted 27 April 2014.

P.M. Christensen. Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, August Krogh Building,Universitetsparken 13, 2100 KBH Ø, Denmark; Team Danmark (Danish elite sport organization), Copenhagen, Denmark.M.H. Petersen, S.N. Friis, and J. Bangsbo. Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen,August Krogh Building, Universitetsparken 13, 2100 KBH Ø, Denmark.Corresponding author: Jens Bangsbo (e-mail: jbangsbo@ifi.ku.dk).1This paper is a part of a Special Issue entitled Nutritional Triggers to Adaptation and Performance.

1058

Appl. Physiol. Nutr. Metab. 39: 1058–1063 (2014) dx.doi.org/10.1139/apnm-2013-0577 Published at www.nrcresearchpress.com/apnm on 5 May 2014.

somewhat higher than the plasma values observed in humans(�40 �mol/L) after caffeine intake of 5 mg/kg (Battram et al. 2005).Nevertheless, caffeine in a dose of �3 mg/kg has been found toimprove 1500 m running performance (�4min30s) in trained run-ners (Wiles et al. 1992) and 3 km cycling time-trial performance(�380 W mean power for �4.0 min) in trained cyclists (Kildinget al. 2012). Using trained rowers, both caffeine doses of 9 mg/kg(Anderson et al. 2000; Bruce et al. 2000) and 6 mg/kg (Bruce et al.2000; Carr et al. 2011a) in the fasted state have been observed toimprove performance. In contrast, doses from 2–6 mg/kg 3 h post-prandial did not alter performance in sub-elite open-weight row-ers (350 W average for the 2000 m distance), which was speculatedto relate to slower uptake of caffeine in the nonfasted state(Skinner et al. 2010). Since competition in elite sports is seldomperformed in the fasted state, it is of interest and presently un-known whether elite rowers can benefit from ingestion of caf-feine in the nonfasted state as was observed in cyclists (Kildinget al. 2012), and from a low dose of caffeine (3 mg/kg) to reduce sideeffects from higher doses (6 mg/kg) such as hand tremor andirregular heartbeat (Carr et al. 2011a).

Blood bicarbonate buffers H+ ions released from contractingmuscle during intense exercise, and consequently, blood bicar-bonate and blood pH is reduced during intense exercise such as2000 m rowing (Nielsen et al. 2002). Oral bicarbonate intake there-fore increases blood buffering capacity and in turn resting bloodpH is increased (Carr et al. 2011b) leading to a larger diffusionalgradient for H+ ions from muscle to plasma. Importantly, bicar-bonate intake has been found to reduce intracellular acidificationduring intense handgrip exercise (Raymer et al. 2004) and re-peated intense cycling (Costill et al. 1984). This may be of func-tional importance, since low muscle pH has been implicated inreduced muscular function (Fitts 2008). In addition, citrate intake,which also increases blood buffer capacity, has been observed tolower interstitial accumulation of potassium, likely due to re-duced interstitial H+ ion accumulation (Street et al. 2005). Sinceinterstitial potassium has been associated with muscle fatigue(McKenna et al. 2008) this may also be a mechanism by whichbicarbonate becomes ergogenic. Lastly, it may be that the higherblood pH after oral bicarbonate intake improves muscle oxygendelivery, since venous bicarbonate infusion during 2000 m rowingmaintained arterial pH, which reduced arterial desaturation andimproved performance (Nielsen et al. 2002). However, whetherthis mechanism is present with oral bicarbonate intake is notclear. Oral bicarbonate has been shown to improve intense endur-ance performance in trained runners in a 1500 m run (�4min10s)(Bird et al. 1995) and in trained cyclists in maximal tests lastingaround 4 min (average power �400 W) (Bellinger et al. 2012;Kilding et al. 2012), whereas time to exhaustion (�7 min) duringconstant load exercise was unaffected by bicarbonate intake(Linderman et al. 1992). Similar contradictive observations havebeen reported for trained rowers with both improved (McNaughtonand Cedaro 1991) and unchanged performance (Brien and McKenzie1989; Carr et al. 2011a, 2012; Kupcis et al. 2012). Part of the discrep-ancy may relate to gastric discomfort and nausea being a commonobservation with bicarbonate intake, which in turn appears to beaugmented when consumed in the fasted state on an empty stom-ach (Carr et al. 2011a), but symptoms may also be present whencombined with a meal (Carr et al. 2011c).

Apparently, both caffeine and bicarbonate ingestion may im-prove high intensity endurance performance in trained athletes,but knowledge is limited with respect to whether the 2 substancescombined provide an additive effect on performance. In cycling,both substances alone and combined were ergogenic relative to aplacebo condition in a 3 km time-trial, but no additive effect wasseen with when the supplements were combined (Kilding et al.2012). In contrast, only caffeine improved 2000 m rowing perfor-mance, whereas the effects on performance from bicarbonatetaken alone or in combination with caffeine were unclear, likely

due to gastric discomfort from the bicarbonate intake (Carr et al.2011a).

Thus, this study examined whether caffeine and bicarbonateingestion alone and in combination would improve competitiveperformance in top-class rowers in the nonfasted state. We hypo-thesized that caffeine and bicarbonate used alone would improverowing performance, and that the combination of the 2 sub-stances would elicit the best performance, since the 2 substancesappear to act through different mechanisms.

Materials and methods

SubjectsTwelve international level rowers: 6 male open-weight (mean ±

SD; 25 ± 1 years of age, 92 ± 3 kg); 5 male light-weight (24 ± 3 years,75 ± 3 kg); and 1 female light-weight rower (27 years, 63 kg) par-ticipated in the study, with the majority of the participants havingexperience from the European or the World championships. Theexperimental procedures were approved by the local ethical com-mittee of the capital region in Copenhagen (Region Hovedstaden),and the rowers were informed about the study procedures and pos-sible discomforts and gave their written consent to participate.

Experimental overviewEach rower performed four 6 min maximal rowing tests after

being supplemented with caffeine (CAF; 3 mg/kg administered aspills), sodium bicarbonate (SB; 0.3 g/kg administered in capsules),caffeine and sodium bicarbonate (CAF + SB; in the same dosesdescribed above), or a placebo (PLA; dextrose as the caffeine pla-cebo and calcium as the sodium bicarbonate placebo adminis-tered in the same number of pills and capsules as above). Placebopills and capsules were also provided to the CAF and SB groups. Adouble-blind randomized design was used. Testing was performedduring the indoor season within a 1 week period, hence rowerswere expected to be in a stable physical condition. On days beforetesting, moderate intensity training was performed (�60 min at�75% of the heart-rate reserve). Subjects were instructed to ab-stain from coffee and other caffeine containing products for 36 hbefore the scheduled testing. Moreover, they were instructed toconsume their last meal 3 h before testing, with instructions fortheir typical routine for diet and fluid ingestion before trainingduring all trials. The light-weight rowers were not making weightfor the performance tests. Hence, only minor differences werelikely present for total energy intake and energy distribution aswell as sodium and water intake.

Performance testsThe rowers were instructed to cover the largest possible dis-

tance during the 6 min maximal test. Apart from total distance,mean power was calculated for the entire test duration and in1 min intervals. The test was performed indoors on a rowing er-gometer (Concept II, Vermont, USA) in a well-ventilated roomwith stable temperature (�20 °C). During the test, the rowers wereallowed to see a display showing their pace (time/500 m) and timeelapsed, since these are important tools for the rowers to pacethemselves, and thus included to reduce day-to-day variation inperformance and to maximize performance. No verbal supportwas given during the tests. All subjects had tried the performancetest numerous times, thus no familiarization test was performed.Prior to the performance test, a 20 min standardized warm-up wasperformed, with the first part encompassing moderate intensityfor 9 min (�45% of the mean power output based on each rowerspersonal best in previous 6 min maximal tests; MP PB 6 minmaximal). Thereafter, 10 min encompassing five 40 s intervalswith increasing intensity (70%–100% of MP PB 6 min maximal)separated by 80 s of low intensity rowing was performed. In thelast minute, 10 maximal strokes were performed followed by lowintensity rowing. Thereafter a 7 min rest period took place beforethe initiation of the performance test. Both the warm-up procedure

Christensen et al. 1059

Published by NRC Research Press

and the recovery length are very similar to the methods used bythe rowers during competitions. In the last minute before com-mencing the performance test the rowers were asked about their“readiness” on a scale from 1 (lowest) to 10 (highest). On an iden-tical scale, each rower also reported on their level of stomachdiscomfort before the test as well as perceived exertion during theperformance test when finished.

Supplementation proceduresSB (or placebo) was consumed with water ad libitum (�500–

750 mL) 75 min prior to start of the performance test. This is aprocedure in accordance with most studies showing a perfor-mance enhancement after bicarbonate intake with a dose andtiming known to raise both blood bicarbonate and pH levels (Carret al. 2011b). CAF (or placebo) was ingested with water 45 min priorto the performance test, and this is also in accordance with previ-ous studies that have reported improved performance after caf-feine intake (Carr et al. 2011a). Subjects provided an estimateddaily consumption of caffeine containing products (coffee, cola,energy drinks) and were distributed among 3 groups termed ei-ther non-users (n = 2), low (�80 mg/day, n = 7), and moderate(�200 mg/day, n = 3). Previous studies have shown that SB intakein hydrated subjects, as in this study, may increase plasma volumeslightly (Lindinger et al. 1999), whereas CAF in some studies maylead to a slight reduction in plasma volume (Maughan and Griffin2003), but this was expected to have minor influence on perfor-mance since subjects were expected to be well hydrated as theywere allowed to drink water in the supplementation period. Insupport, stroke volume is only lowered after 3% dehydration(�2.0–2.5 kg in the group of rowers) (Gonzalez-Alonso et al. 2000)and plasma volume expansion does not appear to improve VO2max

in elite athletes (Warburton et al. 1999). The investigators, whowere following a blind protocol, were present at all times whenthe subjects consumed the substances, but blood samples werenot obtained to verify changes in the blood of the 2 substances orchanges in plasma volume.

StatisticsTotal distance and mean power during the 6 min maximal row-

ing test was evaluated with a one-way analysis of variance (ANOVA)for repeated measures, both for the entire group of rowers (n = 12)and for weight classes separately (open-weight, n = 6; light-weight,n = 6). Readiness and stomach discomfort before the test, andperceived exertion after the test were also evaluated with a one-way ANOVA for repeated measures. Mean power in 1 min intervalswas evaluated using a 2-way ANOVA for repeated measures andusing supplementation and interval as factors. If a significantmain effect or interaction was found a Student–Newman–Keulspost-hoc test was performed to identify the difference. All valuesare the mean ± SD.

Results

PerformanceTotal distance for all rowers covered in the 6 min maximal test

in CAF (1878 ± 97 m) and CAF + SB (1877 ± 97 m) was longer thanPLA (1865 ± 104 m) (P < 0.05) and SB (1860 ± 96 m) (P < 0.01) (Fig. 1A).Relative to PLA, the distance in CAF and CAF + SB was 0.7% longer(P < 0.05) (Fig. 1B). For the light-weight rowers, distance relative toPLA was increased by 1.1% ± 0.8% in CAF and 0.9% ± 0.8% inCAF + SB (P < 0.05), with no difference in the SB group (0.1% ±0.8%). For the open-weight rowers, change in distance relative toPLA was unchanged (0.2% ± 0.9%) in the CAF group, whereas thevalues were 0.4% ± 0.7% in CAF + SB and −0.6% ± 0.9% in SB (Fig. 2).The mean powers for all rowers in the CAF (400 ± 58 W) andCAF + SB groups (400 ± 58 W) were higher than for the PLA (393 ±61 W) (P < 0.05) and SB groups (389 ± 57 W) (P < 0.01). The meanpower was higher (P < 0.05) in the CAF and CAF + SB groups in thelast 3 min of the test compared with PLA, and in the first minuteand the last 3 min of the test relative to SB (Fig. 3). No order effectwas observed, with the average distances of 1868 ± 95, 1869 ± 102,1872 ± 102, and 1871 ± 97 m on the first, second, third, and fourthtest day, respectively.

Fig. 1. Total distance covered in a 6 min maximal test with individual values shown for 12 elite rowers after prior supplementation withplacebo (PLA), caffeine (CAF), caffeine and sodium bicarbonate (CAF + SB), and sodium bicarbonate (SB) expressed in absolute terms (A) andrelative to PLA (B). Open symbols: open-weight rowers (n = 6). Filled symbols: light-weight rowers (n = 6). *, P < 0.05 for CAF and CAF + SBcompared with PLA; ##, P < 0.01 for CAF and CAF + SB compared with SB.

98

99

100

101

102

103

PLA CAF CAF+SB SB

Dis

tanc

e (%

PLA

) 1500

1600

1700

1800

1900

2000

2100

PLA CAF CAF+SB SB

Dis

tanc

e (m

)

*

*

A B # #

# #

*

*

# #

# #

1060 Appl. Physiol. Nutr. Metab. Vol. 39, 2014

Published by NRC Research Press

ReadinessNo differences were observed (P = 0.60 for main effect) for read-

iness before the 6 min maximal test, with values for the variousgroups of 7.9 ± 1.2 for CAF, 7.9 ± 1.4 for CAF + SB, 7.8 ± 0.6 for PLA,and 7.4 ± 1.2 for SB.

Stomach comfortNo differences were observed (P = 0.10 for main effect) in stom-

ach discomfort before the 6 min maximal test among the various

groups, with values of 1.8 ± 1.3 for CAF, 2.4 ± 1.5 for CAF + SB, 1.5 ±0.7 for PLA, and 2.3 ± 1.2 for SB.

Perceived exertionNo differences were observed (P = 0.56 for main effect) for per-

ceived exertion during the 6 min maximal test among the variousgroups, with values of 8.7 ± 1.4 for CAF, 8.8 ± 0.9 for CAF + SB, 8.4 ±1.2 for PLA, and 8.4 ± 0.9 for SB.

DiscussionThe main findings in this study were that the ingestion of caf-

feine, as well as caffeine with sodium bicarbonate, improved6 min maximal rowing performance in highly trained elite row-ers, whereas sodium bicarbonate by itself had no ergogenic effect,and did not lead to gastric discomfort or reduced readiness beforethe tests.

This study also demonstrated that the performance of the eliterowers was improved following caffeine intake at a dose of3 mg/kg body mass in the nonfasted state. In agreement with ourfindings, other studies have observed caffeine as being ergogenicin trained rowers, but they used doses in the range of 6–9 mg/kg inthe fasted state (Anderson et al. 2000; Bruce et al. 2000; Carr et al.2011a), whereas doses from 2–6 mg/kg in the nonfasted state didnot improve performance (Skinner et al. 2010). The contrastingfindings compared with this study are not easily explained, butmay relate to a higher training status of the rowers (internationalclass) participating in this study compared with the study bySkinner et al. (2010), assuming that a lower performance levelleads to a higher variability in the measurement of performance.Accordingly, this is the first study to report that a low dose ofcaffeine in the nonfasted state can improve the performance ofelite rowers, which is supported by observations in trained cy-clists, in the non-fasted state, completing a 3 km time-trial fasterafter a similarly low dose of caffeine (Kilding et al. 2012). Thepresent findings also provide a high external validity for high-performance athletes and their coaches, as the rowers appearedto be at a higher performance level than the participants in mostof the previous studies. The mean power in the 6 min maximaltest for the 6 male open-weight rowers (92 kg) was �435 W,whereas the 5 male light-weight rowers (75 kg) and the femalerower (63 kg) had an average power of �375 W and �255 W,respectively. In comparison, based on reported 2000 m times, theaverage power for male rowers (unknown body mass) was �310 W(Bruce et al. 2000) and �350 W for male open-weight rowers(88 kg) (Skinner et al. 2010). Female rowers (64 kg) averaged�215 W (Anderson et al. 2000), whereas a mixed group of male (n =6; 82 kg) and female (n = 2; 77 kg) rowers averaged 350 W (Carret al. 2011a). Also, the finding that a low dose of 3 mg caffeine/kgwas sufficient to improve performance provides valuable knowl-edge for athletes who suffer side effects from larger doses (Carret al. 2011a) that might reduce the ergogenic properties of caf-feine. The average improvement in distance was �0.7%, corre-sponding to a reduction of about 2 s in the time required to cover a2000 m race distance lasting 6 min, in both caffeine trials relativeto the placebo. Thus, caffeine ingestion may have a large impacton rankings when competing at the highest level, as found for theparticipants in this study, most of whom had experience from theWorld and European championships, and a background that in-cluded several years of training.

However, 3 of the participants did not have their performanceimproved with caffeine relative to the placebo (Fig. 1). Two of the“nonresponders” were drinking coffee on a daily basis, while onewas not. The remaining group consisted of one non-user and row-ers with a low (�80 mg) to moderate daily (�200 mg) intake ofcaffeine. Therefore, habitual caffeine intake does not appear to bea decisive indicator as to whether caffeine ingested just prior tocompeting will improve performance, but it should be noted thatthe subjects were instructed to refrain from caffeine-containing

Fig. 2. Total distance covered in a 6 min maximal test withindividual values shown for open-weight rowers (OW, n = 6; opensymbols) and light-weight rowers (LW, n = 6; filled symbols) afterprior supplementation with placebo (PLA), caffeine (CAF), caffeineand sodium bicarbonate (CAF + SB), and sodium bicarbonate (SB)expressed relative to PLA. *, P < 0.05 for CAF and CAF + SB comparedwith PLA in LW; #, P < 0.05 for CAF and CAF + SB compared with SBin LW; $, P < 0.05 for CAF + SB compared with SB in OW.

98

99

100

101

102

103

OW LW OW LW OW LW OW LW

Dis

tanc

e (%

PLA

)

PLA CAF CAF+SB SB

* *# # $

Fig. 3. Power output during a 6 min maximal test for 12 eliterowers after prior supplementation with placebo (PLA, white bars),caffeine (CAF, black bars), caffeine and sodium bicarbonate(CAF + SB, hatched bars), and sodium bicarbonate (SB, grey bars).Data are the mean ± SD. *, P < 0.05 for CAF and CAF + SB comparedwith PLA;#, P < 0.05 for CAF and CAF + SB compared with SB; ##, P < 0.01 for CAFand CAF + SB compared with SB; ¤¤, P < 0.01 for PLA compared with SB.

350

400

450

500

1 2 3

Time (minutes)

4 5 6

Pow

er (W

)

PLA

CAF

CAF+SB

SB

¤¤ # #

* #

Christensen et al. 1061

Published by NRC Research Press

drinks 36 h preceding scheduled testing. In accordance, the ergo-genic effect of ingesting 3–6 mg caffeine/kg body mass in endur-ance tasks with a duration of 40–60 min was the same whetherhabitual coffee drinkers maintained their daily intake or ab-stained from coffee 4–6 days before testing (Van Soeren andGraham 1998; Irwin et al. 2011). It may be that the diuretic prop-erties from caffeine reported by some (Maughan and Griffin 2003)caused a lower plasma volume in the nonresponders that mayhave abolished the caffeine's ergogenic properties, owing to alower stroke volume such as is seen under conditions of dehydra-tion (Gonzalez-Alonso et al. 2000). However, this is consideredunlikely, since the rowers were expected to be adequately hy-drated and, in turn, the participants consumed water while con-suming the caffeine, so water loss was likely minimal and it is onlyafter a 3% dehydration (�2.5 kg weight loss in the open-weightrowers) that stroke volume is reported to be lowered (Gonzalez-Alonso et al. 2000).

Interestingly, when analyzing the performance changes, light-weight rowers appeared to respond better to caffeine comparedwith open-weight rowers (Fig. 2). We have no obvious explanationfor this discrepancy, but given the low number of subjects (n = 6 inboth groups), these results may simply be due to random varia-tion. Nevertheless, a previous study using only open-weight row-ers did not report any benefit from caffeine, even when using amuch larger dose than in this study (6.0 vs. 3.0 mg/kg) (Skinneret al. 2010). Thus, it will be of interest to elucidate in future studieswhether a high body mass or muscle mass per se limits the ergo-genic potential from caffeine.

Caffeine intake, either alone or in combination with bicarbon-ate, improved performance in the last half of the test (4–6 min),whereas initial pacing (0–1 min) was not altered by caffeine(Fig. 3). In contrast, studies in rowing reported that the power inthe first quarter of a 2000 m test was augmented following caf-feine intake with a higher dose (6–9 mg/kg) (Anderson et al. 2000;Carr et al. 2011a). This suggests that the caffeine dosage may havean impact on pacing in rowing, meaning that a high dose mayelicit a more aggressive pacing in the initial part of a race, whichon a speculative note may relate to a greater catecholamine re-sponse with high dosages of caffeine (Graham and Spriet 1995).Owing to the non-invasive nature of this study, the mechanismsby which caffeine improved rowing performance are unknown,but may relate to actions in the nervous system via altered per-ception of pain (Tarnopolsky 2008; Meeusen et al. 2013), and at themuscular level via improved lactate production (Jackman et al.1996) and calcium release (Tarnopolsky 2008) as well as reducedinterstitial potassium accumulation in muscle (Mohr et al. 2011).Perceived exertion was high for all of the participants (8.5–9.0 onaverage, with 10 as the highest value) with no difference betweenthe groups that took caffeine or the placebo. If we accept thatperceived exertion becomes higher as a function of the timeelapsed in the test (e.g., more strenuous after 5 vs. 1 min), thiscould indicate that the capacity to maintain/increase central mo-tor drive in a state with a high degree of perceived exertion isimproved with caffeine, since the last half of the test was executedwith a higher power output in the groups that ingested caffeinethan in the group that ingested the placebo. This in turn couldindicate that the ergogenic properties of caffeine reside in alter-ing pain perception (Tarnopolsky 2008; Meeusen et al. 2013). Agradual build-up of interstitial potassium levels occurs with con-stant load intense exercise, reaching a plateau after around 3 minwith a further increase with higher workloads (Nielsen et al. 2004)that has been linked with the development of fatigue (McKennaet al. 2008). Caffeine has been observed to lower potassium accu-mulation during intense exercise, likely due to a larger catechol-amine response stimulating the sodium–potassium pump (Mohret al. 2011). If improved sodium–potassium pump activation waspresent in the caffeine trials, another mechanism for the im-proved rowing performance in the last half of the test may be that

a higher power output could be maintained for the same degree ofpotassium accumulation, but this hypothesis needs to be investi-gated in future studies.

Performance in the SB group was not better than in the PLAgroup, in contrast to the hypothesis of the study. The intake of thesodium bicarbonate 75 min before the performance test shouldhave been sufficient to increase blood bicarbonate levels (Carret al. 2011b). This is supported by the finding that blood bicarbon-ate was elevated from 26 ± 1 to 33 ± 1 mmol/L in 15 healthy youngsubjects 80 min after ingestion of the same dose and type ofcapsules performed in a separate experiment after this study (S.Jørgensen, Team Danmark, unpublished data). In one study, bicar-bonate intake impaired the ergogenic effects of caffeine on2000 m rowing performance (Carr et al. 2011a), which likely re-lates to the fact that all subjects reported side-effects with bicar-bonate in that study. This was probably due to bicarbonate beingconsumed on an empty stomach, which is in contrast to the pro-cedures in this study, in which sodium bicarbonate intake did notlead to a significant degree of stomach discomfort relative to theplacebo trials. On average, a score of �2 was reported in all con-ditions, with 1 being the lowest possible score on a scale of 10, andlikewise no difference was observed between the SB and PLAgroups for over-all readiness before the performance test. It needsto be considered whether the increased sodium intake followingintake of the capsules increased plasma volume. However, someauthors have reported no change in plasma volume 75 min after asimilar dose of sodium bicarbonate (Mueller et al. 2013), and oth-ers just a small increase (Lindinger et al. 1999), and even if anincrease was present it may have had minor influence on cardiacoutput and VO2max (Warburton et al. 1999). Thus, taken together,the lack of ergogenic effect after sodium bicarbonate ingestiondoes not seem to have been caused by the timing of the intake ofcapsules or discomfort in the stomach, headache, nausea, etc.

The majority of other studies exploring whether oral intake ofsodium bicarbonate is ergogenic in rowing did not find any ben-efit in a 2000 m rowing test (Brien and McKenzie 1989; Carr et al.2011a, 2012; Kupcis et al. 2012), which is in accordance with thefindings from this study. However, one previous study found im-proved performance in rowing (McNaughton and Cedaro 1991)following sodium bicarbonate intake, as was the case in perfor-mance tests having a duration of �4 min in both cycling (Bellingeret al. 2012; Kilding et al. 2012) and running (Bird et al. 1995). Hencerowing appears to be an exercise modality that is less likely to gainan ergogenic effect from improved blood buffer capacity relativeto other types of intense endurance sports. It has been observedthat the addition of arm muscles during leg exercise lowers legblood flow (Secher et al. 1977). Thus, one possible mechanism forthe apparent discrepancy between rowing and other types of ex-ercise such as running and cycling might be that leg blood flow islower in rowing, which could be speculated to reduce leg H+ ionrelease, meaning that the improved buffer capacity is not utilizedto the degree where it reduces intramuscular leg acidification andbecomes ergogenic. Alternatively, it may be that intramuscularacidification is not a determinant of 2000 m rowing performance,or that highly trained rowers have an optimized buffering capac-ity of H+ ions in the muscle and blood (Juel 2008) where oralbicarbonate intake did not elevate the buffering capacity to adegree where it improved performance, as opposed to when usingvenous infusion (Nielsen et al. 2002).

In summary, this study demonstrated that ingestion of a smalldose of caffeine (3 mg/kg), unlike intake of sodium bicarbonate,improved the performance of elite rowers performing 6 min max-imal rowing, with the difference occurring in the last 3 min of thetest. Moreover, the ergogenic effect of caffeine was not reduced bythe addition of sodium bicarbonate, and light-weight rowers ap-peared to gain a greater benefit from caffeine than open-weightrowers.

1062 Appl. Physiol. Nutr. Metab. Vol. 39, 2014

Published by NRC Research Press

Conflict of interest statementThe authors declare that there is no conflict of interest associ-

ated with this study.

AcknowledgementsSusanne Jørgensen, Team Danmark, is acknowledged for ob-

taining and analyzing blood for bicarbonate concentration in thesubgroup of subjects mentioned in the discussion. The study wassupported by Team Danmark (Danish elite sport organization).

ReferencesAllen, D.G., and Westerblad, H. 1995. The effects of caffeine on intracellular

calcium, force and the rate of relaxation of mouse skeletal muscle. J. Physiol.487(2): 331–342. PMID:8558467.

Anderson, M.E., Bruce, C.R., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G.,and Hawley, J.A. 2000. Improved 2000-meter rowing performance in compet-itive oarswomen after caffeine ingestion. Int. J. Sport Nutr. Exerc. Metab. 10:464–475. PMID:11099373.

Battram, D.S., Graham, T.E., Richter, E.A., and Dela, F. 2005. The effect of caf-feine on glucose kinetics in humans — influence of adrenaline. J. Physiol.569: 347–355. doi:10.1113/jphysiol.2005.097444. PMID:16150793.

Bellinger, P.M., Howe, S.T., Shing, C.M., and Fell, J.W. 2012. Effect of combinedbeta-alanine and sodium bicarbonate supplementation on cycling performance.Med. Sci. Sports Exerc. 44: 1545–1551. doi:10.1249/MSS.0b013e31824cc08d. PMID:22330016.

Bird, S.R., Wiles, J., and Robbins, J. 1995. The effect of sodium bicarbonateingestion on 1500-m racing time. J. Sports Sci. 13: 399–403. doi:10.1080/02640419508732255. PMID:8558626.

Brien, D.M., and McKenzie, D.C. 1989. The effect of induced alkalosis and acido-sis on plasma lactate and work output in elite oarsmen. Eur. J Appl. PhysiolOccup. Physiol. 58: 797–802. doi:10.1007/BF02332209. PMID:2548862.

Bruce, C.R., Anderson, M.E., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G.,and Hawley, J.A. 2000. Enhancement of 2000-m rowing performance aftercaffeine ingestion. Med. Sci. Sports Exerc. 32: 1958–1963. doi:10.1097/00005768-200011000-00021. PMID:11079528.

Burke, L.M. 2008. Caffeine and sports performance. Appl. Physiol. Nutr. Metab.33(6): 1319–1334. doi:10.1139/H08-130. PMID:19088794.

Carr, A.J., Gore, C.J., and Dawson, B. 2011a. Induced alkalosis and caffeine sup-plementation: effects on 2,000-m rowing performance. Int. J Sport Nutr.Exerc. Metab. 21: 357–364. PMID:21799214.

Carr, A.J., Hopkins, W.G., and Gore, C.J. 2011b. Effects of acute alkalosis andacidosis on performance: a meta-analysis. Sports Med. 41: 801–814. doi:10.2165/11591440-000000000-00000. PMID:21923200.

Carr, A.J., Slater, G.J., Gore, C.J., Dawson, B., and Burke, L.M. 2011c. Effect ofsodium bicarbonate on [HCO3

−], pH, and gastrointestinal symptoms. Int. J.Sport Nutr. Exerc. Metab. 21: 189–194. PMID:21719899.

Carr, A.J., Slater, G.J., Gore, C.J., Dawson, B., and Burke, L.M. 2012. Reliability andeffect of sodium bicarbonate: buffering and 2000-m rowing performance.Int. J. Sports Physiol. Perform. 7: 152–160. PMID:22634964.

Costill, D.L., Verstappen, F., Kuipers, H., Janssen, E., and Fink, W. 1984. Acid-basebalance during repeated bouts of exercise: influence of HCO3. Int. J. SportsMed. 5: 228–231. doi:10.1055/s-2008-1025910. PMID:6094373.

Fitts, R.H. 2008. The cross-bridge cycle and skeletal muscle fatigue. J. Appl.Physiol. 104: 551–558. doi:10.1152/japplphysiol.01200.2007. PMID:18162480.

Gonzalez-Alonso, J., Mora-Rodriguez, R., and Coyle, E.F. 2000. Stroke volumeduring exercise: interaction of environment and hydration. Am. J. Physiol.Heart Circ. Physiol. 278: H321–H330. PMID:10666060.

Graham, T.E., and Spriet, L.L. 1995. Metabolic, catecholamine, and exercise per-formance responses to various doses of caffeine. J Appl. Physiol. 78: 867–874.PMID:7775331.

Irwin, C., Desbrow, B., Ellis, A., O'Keeffe, B., Grant, G., and Leveritt, M. 2011.Caffeine withdrawal and high-intensity endurance cycling performance.J. Sports Sci. 29: 509–515. doi:10.1080/02640414.2010.541480. PMID:21279864.

Jackman, M., Wendling, P., Friars, D., and Graham, T.E. 1996. Metabolic catechol-amine, and endurance responses to caffeine during intense exercise. J. Appl.Physiol. 81: 1658–1663. PMID:8904583.

Juel, C. 2008. Regulation of pH in human skeletal muscle: adaptations to physicalactivity. Acta Physiol. (Oxf.), 193: 17–24. doi:10.1111/j.1748-1716.2008.01840.x.PMID:18267000.

Kilding, A.E., Overton, C., and Gleave, J. 2012. Effects of caffeine, sodium bicar-

bonate, and their combined ingestion on high-intensity cycling perfor-mance. Int. J. Sport Nutr. Exerc. Metab. 22: 175–183. PMID:22693238.

Kupcis, P.D., Slater, G.J., Pruscino, C.L., and Kemp, J.G. 2012. Influence of sodiumbicarbonate on performance and hydration in lightweight rowing. Int. J.Sports Physiol. Perform. 7: 11–18. PMID:21941012.

Linderman, J., Kirk, L., Musselman, J., Dolinar, B., and Fahey, T.D. 1992. Theeffects of sodium bicarbonate and pyridoxine-alpha-ketoglutarate on short-term maximal exercise capacity. J. Sports Sci. 10: 243–253. doi:10.1080/02640419208729923. PMID:1318390.

Lindinger, M.I., Franklin, T.W., Lands, L.C., Pedersen, P.K., Welsh, D.G., andHeigenhauser, G.J. 1999. Role of skeletal muscle in plasma ion and acid-baseregulation after NaHCO3 and KHCO3 loading in humans. Am. J. Physiol. 276:R32–R43. PMID:9887175.

Maughan, R.J., and Griffin, J. 2003. Caffeine ingestion and fluid balance: a re-view. J Hum. Nutr. Diet. 16: 411–420. doi:10.1046/j.1365-277X.2003.00477.x.PMID:19774754.

McKenna, M.J., Bangsbo, J., and Renaud, J.M. 2008. Muscle K+, Na+, and Cl dis-turbances and Na+–K+ pump inactivation: implications for fatigue. J. Appl.Physiol. 104: 288–295. doi:10.1152/japplphysiol.01037.2007. PMID:17962569.

McNaughton, L., and Cedaro, R. 1991. The effect of sodium bicarbonate on row-ing ergometer performance in elite rowers. Aust. J. Sci. Med. Sport 23: 66–69.

Meeusen, R., Roelands, B., and Spriet, L.L. 2013. Caffeine, exercise and the brain.Nestle Nutr. Inst. Workshop Ser. 76: 1–12. doi:10.1159/000350223. PMID:23899750.

Mohr, M., Nielsen, J.J., and Bangsbo, J. 2011. Caffeine intake improves intenseintermittent exercise performance and reduces muscle interstitial potas-sium accumulation. J. Appl. Physiol. 111(5): 1372–1379. doi:10.1152/japplphysiol.01028.2010. PMID:21836046.

Mueller, S.M., Gehrig, S.M., Frese, S., Wagner, C.A., Boutellier, U., and Toigo, M.2013. Multiday acute sodium bicarbonate intake improves endurance capac-ity and reduces acidosis in men. J. Int. Soc. Sports Nutr. 10: 16. doi:10.1186/1550-2783-10-16. PMID:23531361.

Nielsen, H.B., Bredmose, P.P., Stromstad, M., Volianitis, S., Quistorff, B., andSecher, N.H. 2002. Bicarbonate attenuates arterial desaturation duringmaximal exercise in humans. J. Appl. Physiol. 93: 724–731. doi:10.1152/japplphysiol.00398.2000. PMID:12133884.

Nielsen, J.J., Mohr, M., Klarskov, C., Kristensen, M., Krustrup, P., Juel, C., andBangsbo, J. 2004. Effects of high-intensity intermittent training on potassiumkinetics and performance in human skeletal muscle. J. Physiol. 554: 857–870.doi:10.1113/jphysiol.2003.050658. PMID:14634198.

Raymer, G.H., Marsh, G.D., Kowalchuk, J.M., and Thompson, R.T. 2004. Meta-bolic effects of induced alkalosis during progressive forearm exercise tofatigue. J. Appl. Physiol. 96: 2050–2056. doi:10.1152/japplphysiol.01261.2003.PMID:14766777.

Rosser, J.I., Walsh, B., and Hogan, M.C. 2009. Effect of physiological levels ofcaffeine on Ca2+ handling and fatigue development in Xenopus isolated singlemyofibers. Am. J. Physiol. Regul. Integr. Comp. Physiol. 296: R1512–R1517.doi:10.1152/ajpregu.90901.2008. PMID:19261915.

Secher, N.H., Clausen, J.P., Klausen, K., Noer, I., and Trap-Jensen, J. 1977. Centraland regional circulatory effects of adding arm exercise to leg exercise. ActaPhysiol. Scand. 100: 288–297. doi:10.1111/j.1748-1716.1977.tb05952.x. PMID:920199.

Skinner, T.L., Jenkins, D.G., Coombes, J.S., Taaffe, D.R., and Leveritt, M.D. 2010.Dose response of caffeine on 2000-m rowing performance. Med. Sci. SportsExerc. 42: 571–576. doi:10.1249/MSS.0b013e3181b6668b. PMID:19952822.

Street, D., Nielsen, J.J., Bangsbo, J., and Juel, C. 2005. Metabolic alkalosis reducesexercise-induced acidosis and potassium accumulation in human skeletalmuscle interstitium. J. Physiol. 566: 481–489. doi:10.1113/jphysiol.2005.086801.PMID:15860529.

Tarnopolsky, M.A. 2008. Effect of caffeine on the neuromuscular system —potential as an ergogenic aid. Appl. Physiol. Nutr. Metab. 33(6): 1284–1289.doi:10.1139/H08-121. PMID:19088790.

Van Soeren, M.H., and Graham, T.E. 1998. Effect of caffeine on metabolism,exercise endurance, and catecholamine responses after withdrawal. J. Appl.Physiol. 85: 1493–1501. PMID:9760346.

Warburton, D.E., Gledhill, N., Jamnik, V.K., Krip, B., and Card, N. 1999. Inducedhypervolemia, cardiac function, VO2max, and performance of elite cyclists.Med. Sci. Sports Exerc. 31: 800–808. doi:10.1097/00005768-199906000-00007.PMID:10378906.

Wiles, J.D., Bird, S.R., Hopkins, J., and Riley, M. 1992. Effect of caffeinated coffeeon running speed, respiratory factors, blood lactate and perceived exertionduring 1500-m treadmill running. Br. J. Sports Med. 26: 116–120. doi:10.1136/bjsm.26.2.116. PMID:1623356.

Christensen et al. 1063

Published by NRC Research Press

Copyright of Applied Physiology, Nutrition & Metabolism is the property of CanadianScience Publishing and its content may not be copied or emailed to multiple sites or posted toa listserv without the copyright holder's express written permission. However, users mayprint, download, or email articles for individual use.