Bitter mouth rinse (Gam 2014)

Mouth Rinsing and Ingesting a Bitter SolutionImproves Sprint Cycling Performance

SHARON GAM, KYM J. GUELFI, and PAUL A. FOURNIER

School of Sport Science, Exercise and Health, University of Western Australia, Crawley, Western Australia, AUSTRALIA

ABSTRACT

GAM, S., K. J. GUELFI, and P. A. FOURNIER. Mouth Rinsing and Ingesting a Bitter Solution Improves Sprint Cycling Performance.

Med. Sci. Sports Exerc., Vol. 46, No. 8, pp. 1648–1657, 2014. Purpose: There is evidence that carbohydrate (CHO) mouth rinsing can

improve endurance exercise performance as well as muscle force production and sprint performance. Whether the oral administration of

non-CHO tastants also affects exercise performance is not known. The purpose of this study was to investigate whether mouth rinsing

and ingesting a bitter-tasting solution of quinine improves maximal sprint cycling performance. Methods: Fourteen competitive male

cyclists performed a 30-s maximal cycling sprint immediately after rinsing their mouth for 10 s and then ingesting a 2-mM bitter quinine

solution, plain water, a 0.05% (w/v) sweet aspartame solution, or no solution at all (control). Cycling power output was recorded during

the sprint. Heart rate, perceived exertion, blood lactate, and blood glucose were measured preexercise, immediately postexercise, and

7 min postexercise. Results: Quinine significantly improved mean power output by 2.4%–3.9% compared with the three other conditions

[P e 0.021, effect size (ES) = 0.81–0.85]. Peak power output in the quinine condition was higher compared with the water (3.7%, P =

0.013, ES = 0.71) and control (3.5% P = 0.021, ES = 0.84) conditions but was not significantly different from aspartame (1.9%, P =

0.114, ES = 0.47). There were no significant differences in cycling performance between water, aspartame, and control conditions. There

were no differences in heart rate, perceived exertion, or blood variables between any of the conditions. Conclusion: This study shows for

the first time that mouth rinsing and ingesting a bitter-tasting solution immediately before a maximal sprint exercise can improve

performance. Key Words: QUININE, BITTER TASTE, T2RS, EXERCISE PERFORMANCE, POWER OUTPUT

In recent years, several studies have reported that rinsingthe mouth with a carbohydrate (CHO) solution, withoutingesting it, can improve exercise performance in en-

durance events lasting 1 h or less (5,6,15,20,22,29,31).Although not all studies have found such an ergogenic ef-fect (2,37), their negative findings have been attributed tothe preexercise nutritional status of the participants (2) or alack of sensitivity of the methodology used to measure per-formance (37). With respect to the effect of CHO mouthrinsing on other aspects of exercise performance, some stud-ies have found no effectof CHO mouth rinsing on sprintperformance (7) or maximal strength (27). Others have pro-vided evidence that CHO mouth rinsing does improve sprintperformance and muscle force production (1,17). Indeed,Gant et al. (17) found that the presence of CHO in the mouthincreased maximal voluntary force in the elbow flexors, andBeaven et al. (1) showed that a single 5-s glucose mouth rinseimproved mean power output in the initial sprint of a series of5 � 6-s sprints compared with a noncaloric placebo.

The ergogenic effect of CHO mouth rinsing has been ex-plained by the presence of receptors in the oral cavity, whichwhen stimulated by the presence of CHO send signals thatactivate reward or pleasure centers in the brain, thereby im-proving exercise performance by reducing the perception ofeffort of the exercise (5). This notion is supported by the workof Chambers et al. (6), who showed, using functional mag-netic resonance imaging, that CHO mouth rinsing with bothglucose and nonsweet maltodextrin resulted in the activationof brain areas generally associated with reward, including theanterior cingulate cortex and striatum. It is important to notethat this ergogenic effect of CHO mouth rinsing seems todepend on the caloric content of CHO in the rinse solutionrather than the perception of sweetness per se. Indeed, severalstudies have shown that the administration of nonsweetCHO [maltodextrin (5,6,15)] provides some ergogenic bene-fits, whereas noncaloric artificial sweeteners have no effecton performance (6).

The evidence that the stimulation of CHO receptors inthe oral cavity has the capacity to improve both enduranceand sprint exercise performance raises the obvious questionof whether stimulation of other types of taste receptors byother classes of tastants may also affect exercise perfor-mance. Of interest, studies based on functional magnetic res-onance imaging have shown that the brain areas activated inresponse to the bitter tastant, quinine, overlap to a great extentwith those stimulated by CHO (33,38). Furthermore, quininehas been shown to evoke greater and longer lasting autonomicnervous system (ANS) responses compared with the other

Address for correspondence: Sharon Gam, B.S., School of Sport Science,Exercise and Health, The University of Western Australia, 35 Stirling High-way, Crawley, WA 6009, Australia; E-mail: [email protected] for publication August 2013.Accepted for publication December 2013.

0195-9131/14/4608-1648/0MEDICINE & SCIENCE IN SPORTS & EXERCISE�Copyright � 2014 by the American College of Sports Medicine

DOI: 10.1249/MSS.0000000000000271

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Copyright © 2014 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.

five prototypical tastants [sweet, sour, salty, bitter, and umami(30,32)]. This raises the intriguing possibility that a bitter-tasting mouth rinse may also enhance exercise performance.

In view of the recent findings that CHO mouth rinsingsignificantly improves sprint performance (1), the primaryaim of this study was to investigate whether combiningmouth rinsing with the ingestion of a bitter-tasting solu-tion composed of quinine acutely improves mean and peakpower during a 30-s maximal cycling sprint effort. Mouthrinsing and ingestion were combined to ensure the activa-tion of bitter taste receptors throughout the oral cavity, in-cluding those at the back of the tongue. Because it is unclearhow concentrated the quinine solution should be, it was alsothe purpose of this study to identify the quinine concentration resulting in both maximal bitterness perception andANS activation, without causing side effects such as nausea,and to adopt this quinine concentration to test its effect onsprint performance.

METHODS

Preliminary Study: Dose–Response Relationshipbetween Quinine Concentration and Bitter TastePerception and ANS Responses

Because no previous research has examined the effect ofquinine ingestion on exercise performance, the concentra-tion of quinine to be used in this study was determined ina preliminary study aimed at identifying the quinine con-centration that results in the strongest taste and ANSresponses [skin conductance (SC) and instantaneous heartrate (IHR)] without causing any feelings of nausea.

Participants

Eighteen healthy male volunteers provided written con-sent to participate in this study (mean T SD; age = 26 T 3 yr,body mass index = 24 T 3 kgImj2). All were nonsmokers,did not report any gustatory or olfactory disorders, and werenot taking any medication or experiencing illnesses thatmight alter their sense of taste or smell. Ethical clearancewas obtained from the Human Research Ethics Committeeof The University of Western Australia.

Experimental Design

Participants attended the laboratory for two sessions, eachconducted at the same time of day. First, participants com-pleted a 6-n-propylthiouracil (PROP)-tasting session toassess the sensitivity of the participants to the bitter chemicalPROP. This is because marked interindividual variationshave been reported in bitter-tasting sensitivity, with theability to taste the bitter chemical PROP generally adoptedto compare individuals (34). The next session examined therelationship between the concentration of quinine and bittertaste intensity, ANS responses, and nausea level. Participants

were instructed to avoid eating or drinking anything other thanwater for 1 h before each testing session.

Upon arrival at the laboratory, participants had electrodesplaced at various locations on their hand and chest to al-low for the continuous measurement of SC and IHR, respec-tively (as detailed later). Participants then put on headphones(Monster Beats Solo; Beats Electronics, Santa Monica, CA,USA) through which brown noise was played at a stan-dardized volume (Simplynoise.com) to minimize externalauditory distractions that could interfere with baseline ANSsignals. Participants were instructed to sit comfortably for15 min to adapt to the experimental conditions before com-mencing the session.

Assessment of PROP-Tasting Status

The PROP-tasting status of each participant was assessedby measuring the perceived intensity of PROP comparedwith a reference salt solution using the three-solution testdescribed by Tepper et al. (34). Participants were catego-rized as PROP nontasters, medium tasters, or supertasters.

Assessment of the Dose–Response Relationshipsbetween Quinine Intake and Both Taste andANS Responses

To determine the dose–response relationships betweenquinine intake and both taste and ANS responses, each par-ticipant was required to rinse his mouth with and then ingest25 mL of six solutions of increasing concentrations of quininehydrochloride (Sigma-Aldrich, St. Louis, MO) and six solu-tions of a single NaCl concentration (Sigma-Aldrich). All so-lutions were prepared with doubly deionized water (Direct-Q5 Ultrapure Water System, Millipore, MA). The concentra-tions of quinine were 0, 0.5, 1, 2, 3, and 4 mM. NaCl waspresented in a standardized concentration of 0.1 M to serveas a dishabituator (14). Quinine was selected as the bittertastant in this study because it is safe for human consump-tion [commonly found as the bittering agent in tonic water(13)] and is often used as a bitter tastant in tasting studies (21).

On the day of testing, all solutions were kept at room tem-perature (24-C) and placed on a table in front of the participantin identical plastic cups. At the onset of the test, participantsfirst tasted one of the NaCl solutions then alternated quinineand NaCl solutions. Quinine solutions were presented in orderof ascending concentration because the expected nausea asso-ciated with ingesting the highest concentration of quininewould have the potential to invalidate the assessment of sub-sequent solutions. Each solution was rinsed in the mouth for10 s before being ingested. Immediately after quinine inges-tion, participants gave subjective ratings of taste intensity andhedonic value using a general labeled magnitude scale (glMS)(19) with adjectives altered to specify either intensity or un-pleasantness. Participants also gave ratings of nausea using a100-mm visual analog scale bounded by the descriptors ‘‘nonausea’’ and ‘‘severe nausea.’’ In addition, ANS responseswere recorded continuously during each session (as detailed in

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the next section). The administration of each consecutive so-lution (either quinine or NaCl) took place once SC and HRreturned to baseline levels and were no longer fluctuating (ap-proximately 2–3 min). In the rest period between solutions,participants rinsed their mouth with water ad libitum. Pre-liminary work was performed to ensure that the rest periodbetween consecutive successive quinine exposures at agiven concentration did not result in any significant differ-ences in taste perception.

ANS Measurements

ANS responses to quinine were assessed indirectly bymeasuring SC and IHR. SC (KS) was measured using bi-polar finger electrodes (MLT116F GSR; AD Instruments,Sydney, Australia) placed on the second phalanx of theindex and third digit on the nondominant hand. The ampli-tude of each response was measured as well as the ohmicperturbation duration (OPD) index, which has been shownto reflect the emotional load of the stimulus (36).

IHR (bpm) was recorded from three silver electrodesplaced in a precordial position. The electrode sites were firstshaved, lightly abraded, and cleaned with alcohol wipes be-fore placement of electrodes. The D2 derivation signal (intervalbetween consecutive R waves) was processed and delivered inthe form of instantaneous HR frequency. The IHR responsewas measured as the difference between the prestimulus levelvalue and the maximum increase induced by the stimulus.

The SC electrodes were used with a galvanic skin re-sponse amplifier (FE116 GSR Amp; AD Instruments) inter-faced with a PowerLab data acquisition system (PowerLab2/20; AD Instruments). SC and IHR signals were amplified,filtered, and recorded throughout the sessions with a sam-pling frequency of 10 Hz using the PowerLab system andanalyzed with LabChart 7 software (AD Instruments).

Data and Statistical Analysis

Psychophysical curves were graphed for mean ANS (SC,IHR, and OPD) and subjective (intensity, hedonic value, andnausea) responses across the range of solution concentra-tions. A one-way repeated-measures ANOVA was used tocompare the responses between quinine concentrations fol-lowed by Fisher’s LSD post hoc tests, with differences ac-cepted at P G 0.05 (Statistical Package for the Social Sciencesfor Windows, Version 17.0; SPSS Inc., Chicago, IL). Partic-ipants were then divided into groups based on their PROP-tasting status, with the ANS and subjective responsescompared using a two-way mixed-model ANOVA withFisher’s LSD post hoc tests. All values, unless otherwisestated, are expressed as mean T SEM.

Main Study: Effect of Quinine Administration onSprint Performance

Participants. Fourteen trained male cyclists (mean T SD;age = 30.1 T 5.4 yr, height = 1.84 T 0.09 m, mass = 77.0 T

11.7 kg, V̇O2peak = 61.9 T 7.7 mLIkgj1Iminj1; PROP-tastingstatus = 3 nontasters, 5 medium tasters, and 6 supertasters)were recruited for this study from cycling and triathlon clubs.Participants were fully informed of the testing proceduresbefore their written consent was obtained. However, to min-imize the possibility of a placebo effect, they were deceivedabout the true aims of the study and were instead informedthat the purpose of the study was to determine the effect ofdifferent taste solutions on the metabolic responses to maxi-mal exercise. After completing all trials, participants werepersonally debriefed as to the true aim of the study. Theprocedures were approved by the Human Research EthicsCommittee of The University of Western Australia.

Experimental design. Each participant visited the lab-oratory on five separate occasions, each separated by 7 d andconducted at the same time of day for each participant. Theinitial visit involved the assessment of PROP-tasting statusand V̇O2peak before familiarization with both the mouth rins-ing procedure and the sprint protocol to be used in the sub-sequent experimental trials.

For the following four experimental trials, participantscompleted a 30-s maximal cycling sprint immediately afterrinsing their mouth and ingesting a bitter quinine solution(QUI), plain water (WAT), a sweet aspartame solution (ASP),or a no-rinse control (CON) administered in a randomizedcounterbalanced order. The WAT and the ASP conditionsserved as placebos because neither water nor aspartame mouthrinsing is beneficial for maximal cycling sprint performance(7) or endurance exercise (6).

Initial session. Before investigating the effect of qui-nine on sprint performance, individual differences in PROPtaste perception were determined for each participant (meth-ods as previously described). After the PROP-tasting test,participants completed a V̇O2peak test on an air-braked cycleergometer (Evolution Pty. Ltd., Adelaide, Australia) using theprotocol and equipment described in Gam et al., (16). Afterthe V̇O2peak test, participants were given plain water to rinseand then ingest, after which they completed the sprint proto-col to be used in the subsequent experimental trials to becomeaccustomed to the experimental procedures. Before leavingthe laboratory, participants were given a food and physicalactivity diary and were asked to record all food and drinkintake and physical activity in the 24 h before each experi-mental trial. A copy of the diary from the first trial was re-turned to each participant, and they were asked to replicatethe same diet and activity pattern in the 24 h before each trial(19). Compliance was confirmed upon arrival to the labora-tory for each experimental trial by inspection of food diariesfrom the previous 24 h. Participants were also instructed tofast overnight before each trial and to avoid strenuous exer-cise, alcohol, and caffeine in the 24 h preceding each trial.

Experimental sessions. On arriving at the laboratoryin the morning, participants had their body mass measuredand were fitted with an HR monitor (Garmin Ltd., Olathe,Kansas). They then performed a 4-min light cycling warm-up at 40% of V̇O2peak, followed by a 2- to 3-s practice sprint

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start (Exertech EX-10 front access cycle ergometer; RepcoCycle Company, Huntingdale, Victoria). Seat height wasstandardized for each participant. After a 10-min rest, par-ticipants were given either 0.36 mLIkgj1 body mass of a2-mM quinine HCl solution (QUI; Sigma-Aldrich), plainwater (WAT), or a 0.05% w/v aspartame solution (ASP;Sigma-Aldrich) or were not given any mouth rinse at all(CON). A volume of 0.36 mLIkgj1 was chosen to accountfor differences in body size, with each participant receivingapproximately 25–35 mL of solution per session. Participantswere instructed to rinse their mouth for 10 s and theningest the solution. The solution was ingested after rinsingto ensure that bitter receptors at the back of the tonguewere activated because there is evidence that the strongestsensation of bitterness occurs in that area of the oralcavity (35).

Immediately after ingesting the solution, participants per-formed a 30-s maximal sprint effort, initiated in a standingposition with the preferred foot starting at the 2 o’clock po-sition. Exercise testing was performed immediately after in-gesting the testing solution in order for our findings not tobe confounded by any effect that the gastrointestinal absorp-tion of the solution may have on exercise performance. Thecycle ergometer was interfaced with a customized program(Cyclemax, School of Sport Science, Exercise and Health,The University of Western Australia) to allow for the mea-surement of mean power output for 0–30 s (Pmean), peakpower output (Ppeak), and mean power output for 0–10 s(P0–10), 10–20 s (P10–20), and 20–30 s (P20–30) of the sprint.Fatigue index, which is the rate of power decline during thetest, was also calculated as described by Coppin et al. (11).Participants were instructed to cycle in an all-out mannerfor 30 s without pacing themselves.

Before the commencement of the mouth rinse protocoland at 0 and 7 min postsprint, HR was recorded, and eachparticipant provided subjective RPE (3) and nausea ratings.Nausea ratings were made using a 100-mm visual analogscale anchored with the descriptors ‘‘no nausea’’ and ‘‘ex-treme nausea’’ (26). Immediately after each rating of nau-sea levels were taken, a capillary blood sample (125 KL)was obtained from the fingertip (Clinitubes, Radiometer,Copenhagen) and analyzed immediately for blood lactateand glucose levels using a blood gas analyzer (ABLi 725;Radiometer, Copenhagen, Denmark).

Statistical analysis. The effects of mouth rinse treat-ment on each performance variable were compared usingtwo-way repeated-measures ANOVA followed by Fisher’sLSD post hoc tests, with differences accepted at P G 0.05(Statistical Package for the Social Sciences for Windows,Version 17.0; SPSS Inc.). Cohen’s effect size (ES) statisticswas also used to highlight any trends. A Pearson product–moment correlation was used to evaluate whether PROP-tasting ability (measured by summing the gLMS scores forthe three PROP solutions for each participant) was related toimprovement in sprint performance. All values, unless oth-erwise stated, are expressed as mean T SEM.

RESULTS

Preliminary Study: Dose–Response Relationshipbetween Quinine Concentration and Bitter TasteIntensity and ANS Responses

Subjective responses. As the concentration of qui-nine increased, there were significant increases in the per-ception of taste intensity and hedonic value (P G 0.05; Fig. 1).Nausea ratings were not affected by quinine concentra-tions G4 mM but were higher at 4 mM compared with allother concentrations (P = 0.048; Fig. 1).

Autonomic responses. As the concentration of qui-nine increased, there were significant increases in the re-sponses of SC, OPD, and IHR (P G 0.05; Fig. 2).

Effect of PROP-tasting status on the dose–response relationship between quinine concentra-tion and bitter taste intensity and ANS responses. Ofthe 18 participants, 5 were nontasters, 5 were medium tast-ers, and 8 were supertasters. When participants were groupedinto nontasters, medium tasters, and supertasters, there wereno significant differences between groups for any of theANS variables examined here or for the subjective ratingsof taste intensity and hedonic value (P 9 0.05). However,PROP supertasters did differ from medium and nontastersin that they experienced significant nausea in response tothe ingestion of a 4-mM quinine solution, whereas averagenausea level was not affected by this concentration of qui-nine in both medium tasters and nontasters. This indicatesthat, except nausea level, sensitivity to PROP is not related tothe ANS and perceptual responses to quinine. This is inagreement with other studies (12,21) who have found nocorrelation between PROP sensitivity and sensitivity to otherbitter compounds, including quinine. On the basis of thesefindings and to ensure that no participant experienced nausea inresponse to quinine ingestion, a quinine concentration of 2 mMwas adopted for testing the effect of quinine on sprint perfor-mance, despite being associated with submaximal taste andANS responses compared with higher concentrations.

Main Study: Effect of Quinine Administration onSprint Performance

Nutritional intake and environmental condi-tions. There was no significant difference in either total en-ergy intake (CON 10,464 T 201; QUI 10,573 T 234; WAT10,556 T 230; ASP 10,431 T 231 kJ; P = 0.470) or CHOintake (CON 326 T 24; QUI 325 T 20; WAT 318 T 21; ASP334 T 21 g; P = 0.500) for the 24 h before each experimentaltrial. Laboratory temperature and relative humidity weresimilar between trials (P 9 0.05).

Mean and peak power. There was a significant maineffect of treatment on mean power output for the 30-s sprint(P = 0.007). Post hoc analysis revealed that mean power washigher in QUI compared with CON (P = 0.021), WAT (P G0.001), and ASP (P = 0.018) (Table 1). These differences weresupported by large ES (Table 1). There were no significant


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differences in mean power output between CON, WAT, andASP conditions (P 9 0.05).

The main effect of treatment on peak power approachedsignificance (P = 0.052). Peak power was significantly higherin QUI compared with CON (P = 0.021, ES = 0.84) andWAT (P = 0.013, ES = 0.79) but did not differ signifi-cantly from ASP (P = 0.114, ES = 0.47) (Table 1). Therewere no significant differences in peak power betweenCON, WAT, and ASP (P 9 0.05).

Mean power between 0–10, 10–20, and 20–30 s,fatigue index. P0–10 was significantly higher in QUI com-pared with WAT (P = 0.01, ES = 0.84) but was not sig-nificantly different from CON (P = 0.08, ES = 0.52) or ASP(P = 0.19, ES = 0.48) (Table 1). P10–20 was significantlyhigher in QUI compared with CON (P = 0.02, ES = 0.73),

WAT (P = 0.005, ES = 0.94), and ASP (P = 0.026,ES = 0.69) (Table 1). P20–30 was not significantly differentbetween QUI, CON (P = 0.138, ES = 0.43), and WAT (P =0.138, ES = 0.44) but approached significance in QUI com-pared with ASP (P = 0.059, ES = 0.67) (Table 1). There wereno significant differences in P0–10, P10–20, or P20–30 betweenCON, WAT, and ASP conditions (P 9 0.05). There were noeffects of treatment on fatigue index (P = 0.646) betweenexperimental conditions.

PROP-tasting and sprint performance. Of the 14participants, 3 were nontasters, 5 were medium tasters, and 6were supertasters. No correlation was found between sensi-tivity to PROP and any of the improvements in mean power(r2 = 0.046, P = 0.877), peak power (r2 = 0.088, P = 0.765),P0–10 (r

2 = 0.071, P = 0.810), P10–20 (r2 = 0.051, P = 0.862),

FIGURE 1—Psychophysical curves for subjective ratings relative to baseline of taste intensity (A), hedonic rating (B), and nausea level in allparticipants (C) (left column) as well as in PROP supertasters (¸), medium tasters (h), and nontasters (0; right column). ‘‘a’’ indicates a significantdifference from preceding concentration level in all participants, ‘‘b’’ indicates a significant difference from preceding concentration level in all PROPgroups, and ‘‘c’’ indicates a significant difference from preceding concentration level in supertasters only (P G 0.05). Values are expressed as mean TSEM (n = 18).


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or P20–30 (r2 = 0.069, P = 0.814). Furthermore, all par-ticipants were able to taste the QUI and the ASP solutionsand described them with the appropriate descriptor (e.g.,bitter, sweet).

HR and subjective ratings. Within each trial, bothHR and RPE increased significantly in response to the 30-ssprint (P G 0.05), before decreasing during the 7-minpostsprint period. HR and RPE were similar at all timepoints between the four experimental treatments (P 9 0.05;Fig. 3). Likewise, nausea ratings were similar between trialsat all time points (P 9 0.05; Fig. 3).

Blood variables. The blood lactate responses to the30-s sprint were similar between trials (P 9 0.05; Fig. 3),although this variable did change significantly within trialsin response to exercise (P G 0.05; Fig. 3). There were also

no differences in blood glucose concentration between trials(P 9 0.05; Fig. 3).

DISCUSSION

There is evidence that CHO mouth rinsing improvesendurance exercise performance as well as muscle forceproduction and maximal sprint performance (1,5,6,15,17,20,22,29,31) via the stimulation of CHO taste bud receptorsin the oral cavity. This raises the issue of whether the oraladministration of non-CHO tastants may also affect exer-cise performance. This study shows for the first time thatmouth rinsing with a bitter-tasting quinine solution followedby its ingestion immediately before a maximal 30-s cyclingsprint can improve performance. A significant 2.4%–3.9%

FIGURE 2—Psychophysical curves for SC amplitude (A), OPD (B), and IHR (C) in all participants (left column) as well as in PROP supertasters (¸),medium tasters (h), and nontasters (0; right column). ‘‘a’’ indicates a significant difference from preceding concentration level, and ‘‘b’’ indicatessignificant difference from preceding concentration level in all PROP groups (P G 0.05). Values are expressed as mean T SEM (n = 18).


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improvement in mean power output was observed with theadministration of quinine compared with an aspartame solu-tion, a water solution, and a no-rinse control condition. Peakpower output was also significantly higher (3.5%–3.7%) withquinine compared with water and no-rinse conditions. Therewere no differences in any of the performance measures be-tween aspartame, water, and no-rinse conditions, and there wasno relationship between PROP-tasting status and the magni-tude of the quinine-mediated improvement in performance.

Because the bitter taste of the quinine solution could not bemasked, several precautions were taken to ensure that any er-gogenic effect of quinine on sprint performance was not theresult of a placebo effect. First, participants were deceivedabout the true purpose of the study. They were told that the aimof this study was to examine the effect of different solutions onthe responses of several blood variables (i.e., blood glucoseand blood lactate) to a maximal sprint. To further minimize thepossibility of a placebo effect, two placebo treatments wereadministered, namely, a plain water solution and a sweet as-partame solution, both known not to enhance performance(6,7). Given the absence of significant differences in any of theperformance or subjective measurements between water, as-partame, and no-rinse conditions, it is unlikely that a placeboeffect occurred in response to quinine intake.

Consistent with the fact that this study followed a counter-balanced experimental design, there was no order effect oftrial administration for any of the performance variablesmeasured (P 9 0.05), indicating that the familiarization trialwas sufficient to negate any learning effects. In addition, thecoefficient of variation between the familiarization sprint(which included a water rinse) and the water rinse experi-mental sprint was 2.13% and 2.20% for mean and peak poweroutput, respectively, suggesting limited variability with thecompetitive cyclists and the performance test used in this

study. The relative improvements in performance observedusing quinine compared with the control conditions (3.9%)is high enough to be important for competitive athletes be-cause Paton and Hopkins (28) have asserted that the smallestworthwhile enhancement in power output for competitivetrack cyclists in events lasting G60 s is approximately 0.5%–1%. Whether the performance in other sprint events lastingless than 30 s (e.g., 100 and 200 m track sprint) would alsobenefit from quinine administration remains to be determined.

The mechanisms underlying the ergogenic benefits of quinineadministration on sprint performance remain to be elucidated.One possibility is that quinine improves sprinting performancein a way similar to that proposed for CHO mouth rinsing byaltering the perception of effort, motivation, and/or arousal levelof the participants during exercise, allowing them to exercise at ahigher intensity (5,29). Evidence that this may be the case here isthe observation that RPE did not differ between quinine andother conditions despite the higher mean and peak power in thequinine trial. Because glucose ingestion has been reported tofacilitate corticomotor output to both fresh and fatigued muscles(17), quinine administration may also have this effect. Theaforementioned proposed mechanisms are consistent with thefindings that there is marked overlap between the brain regions(e.g., anterior cingulate cortex, nucleus accumbens) stimulatedby CHO and quinine (33,38).

The unpleasantness associated with the strong bitter tasteof quinine may also have played a role in its ergogeniceffect. Exposure to unpleasant visual stimuli has been foundto result in improved reaction times and increased muscleforce production in an isometric wrist extension task (9,10)as well as increased corticomotor excitability (8,10) com-pared with viewing neutral and pleasant stimuli. Negativetaste stimuli may act in a similar way, thus providing supportfor the ‘‘negative brain theory’’ (4) that the pattern of brain

TABLE 1. Peak power (Ppeak) and mean power output (Pmean) during a 30-s maximal sprint and various periods within the sprint (P0–10,10–20, 20–30) after mouth rinsing and Ingestion withquinine (QUI), aspartame (ASP), water (WAT), or no-rinse control (CON) (n = 14; mean T SEM)

Performance Variable Treatment Result Mean Relative Change from QUI (%); ES P Mean Relative Change from CON (%); ES P

Pmean (W) QUI 917 T 47CON 882 T 50 j3.9%; 0.83 0.021*WAT 882 T 51 j3.9%; 0.85 0.020* 0.0%; 0.00 1.000ASP 895 T 48 j2.4%; 0.81 0.018* 1.5%; 0.33 0.253

Ppeak (W) QUI 1291 T 84CON 1247 T 83 j3.5%; 0.84 0.021*WAT 1245 T 82 j3.7%; 0.79 0.013* j0.2%; 0.03 0.915ASP 1267 T 81 j1.9%; 0.47 0.114 1.6%; 0.34 0.235

P0–10 (W) QUI 1132 T 73CON 1072 T 78 j5.6%; 0.52 0.082WAT 1086 T 79 j4.2%; 0.84 0.010* 1.3%; 0.13 0.652ASP 1112 T 68 j1.7%; 0.48 0.104 3.8%; 0.39 0.185

P10–20 (W) QUI 901 T 44CON 880 T 45 j2.4%; 0.73 0.020*WAT 876 T 45 j2.9%; 0.94 0.005* j0.5%; 0.12 0.657ASP 878 T 47 j2.6%; 0.69 0.026* j0.2%; 0.06 0.832

P20–30 (W) QUI 707 T 31CON 693 T 33 j2.0%; 0.43 0.138WAT 691 T 34 j2.3%; 0.44 0.138 j0.2%; 0.03 0.918ASP 695 T 36 j1.7%; 0.67 0.059 0.3%; 0.06 0.832

Fatigue index (%) QUI 45 T 3CON 49 T 3 7.4%; 0.51 0.474WAT 47 T 3 5.1%; 0.47 0.408 j2.5%; 0.16 0.725ASP 50 T 3 9.1%; 0.59 0.128 1.9%; 0.06 0.830

*Indicates significant difference (P G 0.05).


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activation in response to a negative or unpleasant stimulusfavors urgent processing and action (23). Whether the un-pleasantness of the strong bitter taste of quinine contrib-utes to its ergogenic effect on sprint performance remains tobe determined.

It is important to note that although quinine was chosenas the bitter tastant in this study, thousands of structurallydiverse compounds elicit bitter taste. Moreover, there aremore than 25 mammalian bitter taste receptors [known asT2Rs (24)], and each responds to several different bitter com-pounds. Some of these receptors are very broadly tuned,recognizing bitter compounds with diverse structural ele-ments, whereas others only recognize tastants with specificstructures (25). Therefore, it is possible that different bittertastants may or may not affect exercise performance in thesame manner as quinine. In addition, the localization of the

T2Rs along the upper gastrointestinal tract is another fac-tor that may mediate the effect of bitter tastants on exerciseperformance. Although T2Rs are found in taste buds in allregions of the oral cavity, there is evidence that bitternessis sensed most strongly in the circumvallate papillae wherethe taste buds are located in a V-shaped line at the back ofthe tongue and are innervated by the glossopharyngeal nerve(35). Because bitter taste is typically associated with sub-stances that are potentially toxic or harmful, the T2Rs inthe circumvallate papillae may serve as the last line of de-fense against the ingestion of these substances (24), thus ex-plaining the strongest sensation of bitterness. It is for thisreason that the 10-s mouth rinse was combined with inges-tion in this study to maximally activate as many bitter re-ceptors in the oral cavity as possible, including those at theback of the tongue. It is unclear, however, whether mouth

FIGURE 3—Effect of mouth rinsing and ingesting solutions composed of 2 mM quinine HCl (QUI), plain water (WAT), 0.05% w/v aspartame (ASP),and a no-solution control condition (CON) on HR (A), blood glucose level (B), blood lactate level (C), RPE (D), and nausea score (E) at 5 minpreexercise (h), immediately postexercise (h), and 7 min postexercise (Ì). HSignificant difference from preexercise, P G 0.05. Values are expressed asmean T SEM (n = 14).


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rinsing alone or ingestion alone without prolonged mouthrinsing with quinine would be sufficient to produce an ergo-genic effect comparable to that attained here with combiningmouth rinsing and ingestion of quinine.

Other factors likely to impact the effect of quinine onsprinting performance include the concentration and timingof quinine administration. A concentration of 2 mM was usedin the current study because we showed that at this level qui-nine did not cause any nausea, irrespective of one’s PROP-tasting status. Given that stronger ANS responses wereobserved in response to higher quinine concentrations andthat not all participants experienced nausea under theseconditions, it is possible that ingesting quinine at more than2 mM may further improve sprint performance in some in-dividuals. The time elapsed between quinine administrationand sprint performance is another factor that may affect thebenefits of quinine. This notion is supported by the observa-tion that the ANS responses to quinine last for no more than

80–120 s (30,32), thus suggesting that for quinine to be be-neficial, exercise should be performed immediately afterquinine intake.

In conclusion, this study shows for the first time thatmouth rinsing and ingestion of a quinine solution immedi-ately before a maximal 30-s sprint can improve mean andpeak power output. These findings are likely to be mean-ingful for sprinters or power athletes involved in short du-ration events. The mechanisms underlying the effect ofquinine remain to be elucidated, as well as the effect ofquinine (or other bitter tastants) mouth rinsing and inges-tion on different modes of exercise, including enduranceand resistance exercise.

The authors would like to thank all the participants for their timeand effort. No funding was received for this study.

There are no conflicts of interest for any of the authors.The results of the present study do not constitute endorsement by

the American College of Sports Medicine.

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Bitter mouth rinse (Gam 2014)

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