Caffeine Mouth Rinse Does Not Improve Time to Exhaustion in Male Trained Cyclists
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
International Journal of Sport Nutrition and Exercise Metabolism, 2021, 31, 412-419
https://doi.org/10.1123/ijsnem.2020-0360
© 2021 Human Kinetics, Inc. ORIGINAL RESEARCH
Caffeine Mouth Rinse Does Not Improve Time
to Exhaustion in Male Trained Cyclists
Lara Lima Nabuco Bryan Saunders
University of Brasília University of São Paulo (USP)
Renato André Sousa da Silva Guilherme Eckhardt Molina
Euro American University Center and Caio Eduardo Gonçalves Reis
and University of Brasília University of Brasília
This study investigated the effects of caffeine mouth rinse on cycling time to exhaustion (TTE) and physiological responses in
trained cyclists. In a double-blinded randomized counterbalanced cross-over design, 10 recreationally trained male cyclists (mean ±
SD: 32 ± 3 years, 72.8 ± 5.3 kg, 1.78 ± 0.06 m, 13.9% ± 3.3% body fat, peak power output = 289.4 ± 24.7 W) completed two TTE
tests cycling at 75% of peak aerobic power following 24 hr of dietary and exercise standardization. Cyclists were administered 25-
ml mouth rinses for 5 s containing either 85 mg of caffeine or control (water) every 5 min throughout the exercise tests. No
significant improvement in TTE was shown with caffeine mouth rinse compared with control (33:24 ± 12:47 vs. 28:08 ± 10:18 min;
Cohen’s dz effect size: 0.51, p = .14). Caffeine mouth rinse had no significant effect on ratings of perceived exertion (p = .31) or heart
rate (p = .35) throughout the cycling TTE protocol. These data indicate that a repeated dose of caffeinated mouth rinse for 5 s does
not improve cycling TTE in recreationally trained male cyclists. However, these findings should be taken with caution due to the
small sample size and blinding ineffectiveness, while further well-design studies with larger samples are warranted.
Keywords: ergogenicity, exercise tolerance, suplements
Recent meta-analyses have demonstrated the ergogenic effects drinks, gels, bars, chewing gum, nasal spray, and, more recently, as a
of caffeine supplementation on endurance exercise performance caffeine mouth rinse (Caff-MR) (Wickham & Spriet, 2018).
(Grgic et al., 2020; Shen et al., 2019; Southward et al., 2018). Caffeine ingestion can result in several unwanted side effects,
Caffeine ingestion is presumed to enhance performance primarily with anxiety, insomnia, and urgent urination and defecation most
via central and peripheral adenosine receptor antagonism (A1- and frequently reported by athletes after caffeine intake and which can
A2A-receptors) (Meeusen et al., 2013; Ribeiro & Sebastio, 2010). occur in a linear dose-dependent manner (>6 mg/kg), primarily in
Via these actions in the central nervous system, caffeine’s positive caffeine-sensitive individuals (Guest et al., 2021). To avoid these
effects likely occur through reduced pain perception and decreased effects, Caff-MR emerges as an alternative supplementation form
ratings of perceived exertion (RPE), which can mitigate fatigue, that may provide possible ergogenic effects while minimizing the
thereby improving exercise performance (Meeusen et al., 2013; risk of side effects. In addition, Caff-MR might be interesting for
Wickham & Spriet, 2018). those involved in evening sport to avoid sleep issues associated
In 2018, caffeine was recognized by the International Olympic with caffeine use in the afternoon/evening, particularly in caffeine-
Committee as a substance with robust evidence of achieving benefits sensitive individuals.
to performance when ingested approximately 60 min before exercise Some studies have shown significant improvements in exercise
at a dose of 3–6 mg/kg (Maughan et al., 2018). Caffeine can be performance with Caff-MR, specifically during repeated short-
administered in various forms, such as capsules, coffee, energy duration cycling sprints (Beaven et al., 2013; Kizzi et al., 2016),
30-min cycling time trial (TT) (Bottoms et al., 2014), and 30-min arm
cranking TT (Sinclair & Bottoms, 2014). In contrast, other studies
Nabuco is with the Human Nutrition Graduate Program, School of Health Science, have demonstrated no significant effects of Caff-MR on 60-min
University of Brasília, Brasília, Brazil; and the Laboratório de Bioquímica da cycling (Doering et al., 2014), 3-km cycling TT (Pataky et al., 2016),
Nutrição, Núcleo de Nutrição e Medicina Tropical, Universidade de Brasília, muscle strength (Clarke et al., 2015), intermittent running (Dolan
Brasília, Brazil. Saunders is with the Applied Physiology and Nutrition Research et al., 2017), and 30-s anaerobic Wingate performance (Marinho
Group, School of Physical Education and Sport; Rheumatology Division, Faculdade et al., 2020). A recent systematic review indicated that more research
de Medicina FMUSP, University of São Paulo (USP), São Paulo, SP, Brazil; and the is warranted to elucidate the effects of Caff-MR on exercise perfor-
Institute of Orthopaedics and Traumatology, Faculty of Medicine FMUSP, Univer-
mance (Ehlert et al., 2020). Furthermore, no previous study has
sity of São Paulo, Brazil. Silva is with the Laboratory of Physical Performance and
Healthy, Faculty of Physical Education, Euro American University Center, Brasilia,
evaluated the effects of Caff-MR on exercise capacity, such as a
Brazil. Silva and Molina are with the Laboratory of Exercise Physiology, Faculty of cycling time to exhaustion (TTE) protocol, which might have
Physical Education, University of Brasília, Brasilia, Brazil. Reis is with the important implications for athletes who are required to exert them-
Department of Nutrition, School of Health Science, University of Brasília, Brasília, selves to the point of exhaustion or near exhaustion (e.g., domestiques
Brazil. Nabuco (laranabuco@hotmail.com) is corresponding author. in cycling or athletes trying to maintain race pace with the leader).
412
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTCCaffeine Mouth Rinse and Cycling to Exhaustion Performance 413
The present study aimed to investigate the effects of Caff-MR Anthropometric and Body Composition
on cycling TTE and physiological responses in male cyclists. Measurements
Body weight was measured using an electronic platform scale to a
Methods precision of 100 g (model 720; InBody, BioSpace, Seoul, Korea),
height was determined using a portable stadiometer to an accuracy of
Ethics 0.1 cm (Sanny model ES2060, São Bernardo do Campo, Brazil), and
body mass index was computed and classified according to the World
The ethics committee of the University of Brasília approved Health Organization (WHO, 2020). Body fat percentage was mea-
the experimental protocol in August 2019 (CAAE: 06764918. sured by multifrequency bioelectrical impedance according to the
4.0000.0030) in accordance with the Declaration of Helsinki. The manufacturer’s instructions. Participants were asked to empty their
trial was registered in the Brazilian Registry of Clinical Trials bladder immediately before these measurements. They were instructed
(ReBEC) under registration number RBR-65dynt. All partici- to wear light clothing and remove metallic adornments for the sessions.
pants were fully informed about the study protocol, possible risks, They were required to be overnight fasted (10–12 hr fluid and food
and provided written informed consent. This trial was described restriction), and not to have drunk alcohol for 48 hr or caffeine 24 hr
according to the criteria and recommendations of the Proper prior to tests. They were also required not to have performed strenuous
Reporting of Evidence in Sport and Exercise Nutrition Trials physical activity in 24 hr prior to the exercise tests.
(Betts et al., 2020).
PPO Determination
Experimental Design
The incremental cycle ergometer protocol was performed to deter-
This was a double-blind, counterbalanced, randomized, cross- mine the PPO of each participant. The test started following a 10-
over study. Participants underwent two experimental tests: Caff- min warm-up at 100 W. Each stage lasted 150 s, the first performed
MR and water mouth rinse (control [CON]) solutions, with 7 days at 3.3 W/kg, increasing by 50 W for the second stage, followed by
between tests. Participants were randomly assigned to the alloca- 25 W increases per stage until exhaustion (Hawley & Noakes,
tion sequence (a) “Caff-MR → CON” or (b) “CON → Caff-MR” 1992). Participants received strong verbal encouragement to con-
using a simple randomization procedure (Microsoft Excel spread- tinue for as long as possible. The test ended at the point of voluntary
sheet, Albuquerque, Novo México, EUA) to generate an equal exhaustion or when participants were unable to maintain a cadence
number of participants in each treatment order. Thus, half (n = 5) of 80–90 revolutions per minute (rpm; Cotshall et al., 1996).
of the participants followed “Caff-MR → CON” and the other half Individual PPO was calculated as the last completed stage plus
(n = 5) the “CON → Caff-MR” order. the fraction of time spent in the final noncompleted stage multiplied
by 25 W (Kuipers et al., 1985).
Participants
The inclusion criteria consisted of males, 20–40 years old, cyclists Mouth Rinse Protocol
(≥200 km/week), regular consumers of caffeine (≤500 mg/day), Participants performed a mouth rinse with the caffeine or CON
without any health conditions, allergies, food intolerances, or use solution immediately prior to starting the TTE test, and thereafter
of medication or supplements for at least 30 days before testing every 5 min throughout the exercise until exhaustion. Cyclists
(except carbohydrate, protein, and caffeine). Participants who did rinsed vigorously around the buccal cavity for 5 s and subsequently
not complete all visits or who were unable to complete the first expectorated into a provided opaque container. The Caff-MR
stage of the incremental exercise test to determine peak power solution consisted of 25 ml of water with 85 mg of anhydrous
output (PPO) were excluded from the study. caffeine per dose (0.34%), while CON consisted only of 25 ml of
water. The dose of caffeine administered and mouth rinse protocol
Experimental Sessions was based on previous studies investigating Caff-MR on exercise
performance (Bottoms et al., 2014; Doering et al., 2014; Sinclair &
The participants attended four sessions at the laboratory within a Bottoms, 2014).
15-day period. The initial visit consisted of anthropometric and
body composition measurements, dietary and caffeine intake
assessment, while training and health questionnaires were also
Blinding
administered. On Visit 2, cyclists performed an incremental cycle Caffeine’s bitter taste is difficult to mask, and our CON solution
ergometer protocol (Hawley & Noakes, 1992) to determine PPO, was water. Thus, to deceive the participants as to what solution they
followed by a familiarization of the TTE test on the cycle ergometer were provided, we informed them they would be allocated to
(CG-04; Inbramed LTDA, Porto Alegre, Brazil). Visits 3 and 4 receive two of four possible solutions: Caff-MR, CON, coffee,
were for the experimental tests performed under standardized or bitter solution. At the end of each TTE test, participants were
laboratory conditions (23–24 °C) between 7:00 and 10:00 a.m. asked to indicate which solution they believed they had ingested
Participants were instructed to refrain from exercise and caffeine out of the four described possibilities (Caff-MR, CON, coffee, and
for 24 hr, and alcohol for 48 hr, prior to each experimental test and bitter solution). Coffee and bitter solution were chosen since both
to maintain regular training and dietary intake during the study have a bitter taste similar to that of the Caff-MR. The decision not
period. Prior to the TTE tests, participants confirmed adherence to to use a noncaloric bitter water as a placebo treatment was taken
the pretrial dietary and exercise recommendations and were asked due to the interaction between caffeine and oral bitter receptors in
about any medication or supplements used in the last 7 days. If any the oral cavity linked to ergogenic effects (Pickering, 2019). It is
individual reported medication or supplement use, the TTE test was speculated that bitter taste may lead to ergogenic effects due to the
delayed by a further 7 days. interaction with bitter and caffeine receptors found in the mouth
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTC414 Nabuco et al.
and that bitter tastants can activate certain areas of the brain related participants were characterized as low (0–150 mg/day), moderate
to motor control and emotion processing (Best et al., 2020; Poole & (150–300 mg/day), and high (>300 mg/day) caffeine consumers.
Tordoff, 2017; Zald et al., 2002). This hypothesis could increase
the risk of bias regarding the effectiveness of caffeine solution. The Statistical Analysis and Calculations
effectiveness of the blinding process was examined using the new
blinding index (newBI) (Bang et al., 2004), which estimates the The Shapiro–Wilk test was used to evaluate the normality of
proportion of individuals who correctly and incorrectly guessed distribution, with all data normally distributed. A paired t test
their assigned treatment. was applied to analyze the differences between Caff-MR and CON
for TTE, HR (mean and maximum), number of mouth rinses, as
well as for dietary consumption (energy, carbohydrates, protein,
Cycling TTE and lipids). Levene’s test was performed to determine the homo-
All cycling tests were conducted on an electronically braked cycle geneity of variance, Mauchly’s test to analyze sphericity which was
ergometer (CG-04; Inbramed LTDA). Participants could self-select followed by a Greenhouse–Geisser adjustment when required.
their cadence based upon their own preference, with pedal cadence General linear models with repeated measures were applied with
maintained between 80 and 90 rpm in a seated position. All tests session as a between-participant factor and time as a within-
were conducted in a postprandial state and in the morning (7:00– participant factor (repeated-measures variable) for HR and RPE
10:00 a.m.). The TTE test was performed at 75% of previously responses with Bonferroni adjustments for post hoc comparisons
determined PPO and started after a 10-min warm-up at 100 W. when a significant interaction was found. Cohen’s dz effect sizes
were calculated for TTE to measure the magnitude of the difference
Participants were considered to have reached volitional exhaustion
between Caff-MR and CON. Thresholds for small, moderate, and
when they stopped pedaling altogether or were unable to maintain
large effects were 0.20, 0.50, and 0.80 (Cohen, 1988). The newBI
the required cadence of 80–90 rpm during 10 consecutive seconds. If
(Bang et al., 2004) was performed to assess the effectiveness of the
cadence dropped below 80 rpm, participants received strong verbal
blinding process. The newBI results in values from −1 to 1 (≤0,
encouragement to maintain the required pedal rate for as long as
blinding success and >0, blinding failure). All statistical analyses
possible. Participants could ingest water (ad libitum) throughout the
were performed using SPSS Statistics for Windows (version 21.0;
exercise protocol. The TTE was recorded as the primary outcome
IBM Corp., Armonk, NY). The criterion for statistical significance
measure. Heart rate (HR) (Polar H10® heart rate transmitter, Polar was p < .05 (two-tailed). Data are presented as mean ± SD.
Electro, Kempele, Finland) (Gilgen-Ammann et al., 2019) and RPE
(Borg, 1982) were recorded immediately prior to initiating the
exercise test (baseline), every 5 min throughout the test, and at Results
the moment of voluntary exhaustion (final). The two experimental
sessions were performed on different days, precisely 7 days apart. Participants
Each participant was tested at the same time of day and same day of
Fifteen male cyclists participated in the study, although five did not
the week to minimize the effects of circadian variation.
complete all visits (four gave up citing personal reasons and one did
not complete the first step of the incremental test—exclusion
Dietary Assessment criteria) (Figure 1). Thus, 10 participants (mean ± SD: age =
Habitual food intake was assessed via three nonconsecutive 24 hr 32 ± 3 years, body mass = 72.8 ± 5.3 kg, height = 1.79 ± 0.06 m,
food records, consisting of 2 weekdays and 1 weekend day body fat = 13.9% ± 3.3%, PPO = 289.4 ± 24.7 W) completed the
(Gibson, 2005). The food records were collected using a specific study between September 2019 and March 2020. The participants
were classified as recreationally trained cyclists based on their
form, with preparation methods, mealtimes, types, and homemade
PPO, according to Pauw et al. (2013).
serving sizes of the consumed foods. The first and second food
records were conducted in person during the initial visit and on the
first experimental test day. The third food record was collected by Time to Exhaustion
telephone on a nonconsecutive day (Conway et al., 2004). All food There was no significant difference in TTE between Caff-MR and
records were checked to ensure accuracy and completeness. Food CON (33:24 ± 12:47 vs. 28:08 ± 10:18 min; p = .14) (Figure 2),
portions were converted into grams and milliliters, and energy and although the difference between conditions was +18.7%
macronutrient intake were calculated using Dietbox software (+5:16 min), which resulted in a small to medium effect size
(version 2.0; Dietbox, São Paulo, Brazil). The food record in (dz = 0.51) for Caff-MR.
the 24 hr prior to the first experimental test was returned to the
participants, and they were instructed to replicate the same food
pattern for the 24 hr period before the second experimental test. On HR and Rate of Perceived Exertion
the second experimental test, a 24 hr food record was collected to There were no significant differences in HR and RPE between
assess the food intake agreement between the 24 hr periods before sessions throughout the cycling test (Session × Time interaction:
the 2 experimental days. p = .35 and p = .31; Figure 3). In addition, no significant differences
Caffeine consumption was evaluated via a questionnaire used were shown for mean HR (Caff-MR = 162 ± 8 bpm; CON =
to assess caffeine consumed over the previous week (Landrum, 160 ± 7 bpm; p = .30) or maximum HR (Caff-MR = 174 ±9 bpm;
1992). Participants were asked to indicate the number of servings CON = 171 ± 6 bpm; p = .46) between conditions.
of coffee, tea, soft drinks, energy drinks, and other caffeine-
containing products consumed. The quantification of caffeine
Caffeine Supplementation
was calculated using reference values provided by the United
States Department of Agriculture in the USDA Food Composition There was no significant difference in the number of mouth rinses
Databases. Based on previous criteria (Pataky et al., 2016), between conditions (Caff-MR = 7.4 ± 2.5 and CON = 6.4 ± 2.1
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTCCaffeine Mouth Rinse and Cycling to Exhaustion Performance 415
Figure 1 — Flow diagram of the participants through the study. Caff-MR = caffeine mouth rinse; CON = control.
times; p = .16). Overall, the total dose of caffeine rinsed was
629 ± 212 mg, which represents 8.6 mg/kg or 1.16 mg/kg per dose.
Food and Caffeine Intake
Three participants were classified as low (93 ± 23 mg/day), three as
moderate (204 ± 41 mg/day), and four as high (356 ± 39 mg/day)
caffeine consumers. Habitual caffeine intake ranged from 80 to
404 mg/day, with a mean of 232 ± 120 mg/day.
Dietary food records 24 hr prior to the experimental tests
showed no significant differences between Caff-MR and CON for
energy (2,275 ± 538 vs. 2,327 ± 402 kcal; p = .68), carbohydrate
(3.35 ± 0.67 vs. 3.40 ± 0.78 g/kg; p = .46), protein (1.50 ± 0.47 vs.
1.46 ± 0.40 g/kg; p = .52), or lipids (1.33 ± 0.55 vs. 1.37 ± 0.49 g/kg;
p = .77) intake.
Blinding Effectiveness
Figure 2 — Time to exhaustion (in minutes) in the Caff-MR and CON
conditions (n = 10). A paired t test was used to compare the groups The newBI scores were 0.4 for Caff-MR and 0.7 for CON, which
(p = .14). Caff-MR = caffeine mouth rinse; CON = control. represent a failure to maintain blinding. Two participants (20%)
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTC416 Nabuco et al.
size shown here (effect size = 0.51) was moderate and in line with
the effect sizes shown for caffeine on endurance exercise (effect
size = 0.2–0.6; Grgic et al., 2020).
The lack of a significant effect shown here might be due, in
part, to the small sample size and/or interindividual variation in
responses. Even though this study showed no statistically signifi-
cant differences between Caff-MR and CON, six participants
presented a ≥20% improvement in TTE with Caff-MR (22–
66%). It is unclear why these individuals had such a large response
but may be attributed to the Caff-MR response and/or a placebo
effect (Saunders et al., 2017, 2019) since four of these participants
correctly guessed they had taken caffeine although two participants
guessed incorrectly and thought they had consumed bitter water,
coffee, or water. The findings of the present study should be taken
with caution due to the small sample size and blinding ineffective-
ness on the mouth rinse protocol while further studies with larger
samples are warranted.
The present study used 85 mg of caffeine per mouth rinse
(0.34%), representing 1.16 mg/kg per dose. This value represents a
low to intermediate dose compared with previous studies with no
significant Caff-MR effects (0.46–4.28 mg/kg per dose) (Clarke
et al., 2015; Doering et al., 2014; Dolan et al., 2017; Marinho et al.,
2020; Pataky et al., 2016). Studies which showed positive results
with Caff-MR similarly varied considerably in the amount of
caffeine contained per dose (0.1–6.0 mg/kg per dose) (Beaven
et al., 2013; Bottoms et al., 2014; Kizzi et al., 2016; Sinclair &
Bottoms, 2014). Thus, it currently remains unclear what the optimal
dose of Caff-MR is to elicit performance improvements.
The mean number of mouth rinses in our study was in accor-
Figure 3 — Variation in average HR (in beats per minute) and RPE
(a.u.) throughout the time to exhaustion test between conditions up to dance with the frequency of some previous studies (Doering et al,
40 minutes. General linear models with repeated measures were used to 2014; Kizzi et al., 2016), although these studies had contrasting
analyze the differences between groups (Group × Time interaction, p = .35 effects on exercise. Large variability in the frequency of mouth
and p = .31). Caff-MR = caffeine mouth rinse; CON = control; HR = heart rinsing of previous studies on different exercise protocols precludes
rate; RPE = ratings of perceived exertion. making any solid conclusions about the ideal frequency (Ehlert et al.,
2020). Thus, large variation and contrasting evidence between
studies currently preclude establishing an optimal dose and fre-
were totally blinded to both interventions (caffeine and control), quency throughout the exercise sessions (Ehlert et al., 2020).
five participants (50%) correctly identified both solutions, and three The large heterogeneity in studies protocols highlights the need
(30%) correctly identified only the CON. Regarding the responders for more standardized and well-controlled research on the topic to
(n = 7), three correctly identified both solutions, while three did not determine the true impact of Caff-MR on exercise and which factors
identify Caff-MR, and one was totally blinded to both interven- (i.e., dosing strategy, exercise mode) might modify these effects.
tions. Regarding the nonresponders (n = 3), two correctly identified Although the mechanism of action for Caff-MR is not entirely
both solutions and one was completely blinded as per the understood, some studies have proposed that it is similar to a
responses. carbohydrate mouth rinse (Chambers et al., 2009) and caffeinated
chewing gum (Wickham & Spriet, 2018). These ergogenic ap-
Discussion proaches have their actions mediated by receptors present in the
oral cavity. When adenosine receptors were identified in the oral
This is the first study to investigate the effect of a repeated Caff-MR cavity in mammals (Rubinstein et al., 2001), it was hypothesized
protocol on endurance exercise capacity in trained male cyclists. that these receptors could increase the absorption of caffeine
The results showed that repeated exposure to 85 mg of Caff-MR through the oral mucosa (Beaven et al., 2013) due to an extensive
solution did not improve cycling TTE and had no effect on RPE or vascularization (Kamimori et al., 2002). However, Caff-MR does
HR of recreationally trained male cyclists. Therefore, the current not appear to increase circulating caffeine (Doering et al., 2014).
data do not support the use of Caff-MR as an ergogenic aid to There is also a proposed interaction between caffeine and bitter oral
improve aerobic exercise capacity. receptors in the oral cavity (Matsumoto, 2013). The activation of
Our results are somewhat in agreement with a recent system- these receptors can stimulate the brain’s regions associated with
atic review on the effects of Caff-MR on exercise performance that reward processing (Wickham & Spriet, 2018; Zald et al., 2002) and
showed no consistent ergogenic effects, with mixed and inconclu- muscle motor output (Kalmar & Cafarelli, 1999). Nonetheless,
sive results (Ehlert et al., 2020). Similarly, a meta-analysis per- more mechanistic research is required to determine how Caff-MR
formed by our research group showed no significant overall effect may exert its ergogenic properties, which will help to optimize
of Caff-MR on several sport performance outcomes (with an supplementation protocols.
overall very small Hedge’s g effect size of 0.17, 95% CI There were no significant differences in RPE or HR between
[−0.07, 0.41]; p = .16) (unpublished data). Nonetheless, the effect conditions. These findings are similar to the results presented by a
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTCCaffeine Mouth Rinse and Cycling to Exhaustion Performance 417
recent systematic review that showed no effect of Caff-MR on
these variables (Ehlert et al., 2020). Even in those studies that References
showed a positive effect of Caff-MR over placebo on sports Bang, H., Ni, L., & Davis, C.E. (2004). Assessment of blinding in clinical
performance, no differences in RPE or HR were shown (Beaven trials. Controlled Clinical Trials, 25(2), 143–156. PubMed ID:
et al., 2013; Bottoms et al., 2014; Kizzi et al., 2016; Sinclair & 15020033 doi:10.1016/j.cct.2003.10.016
Bottoms, 2014). However, since performance was improved in Barreto, G., Grecco, B., Merola, P., Reis, C.E.G., Gualano, B., &
these studies, this likely still accounts to a reduced perception of Saunders, B. (2021). Novel insights on caffeine supplementation,
effort since the RPE:PO ratio is improved, with greater power CYP1A2 genotype, physiological responses and exercise perfor-
output for the same perceived exertion (Barreto et al., 2021). In the mance. European Journal of Applied Physiology, 121(3), 749–
present study, there was no significant effect of Caff-MR on 769. PubMed ID: 33403509 doi:10.1007/s00421-020-04571-7
exercise capacity or RPE. Beaumont, R., Cordery, P., Funnell, M., Mears, S., James, L., & Watson,
Most participants were classified as moderate habitual caffeine P. (2017). Chronic ingestion of a low dose of caffeine induces
consumers. However, it is difficult to say whether this influenced tolerance to the performance benefits of caffeine. Journal of Sports
the effectiveness of Caff-MR. The effect of caffeine habituation on Sciences, 35(19), 1920–1927. PubMed ID: 27762662 doi:10.1080/
the ergogenic effect of caffeine is controversial, with contrasting 02640414.2016.1241421
and limited evidence since few studies accurately measure the Beaven, C.M., Maulder, P., Pooley, A., Kilduff, L., & Cook, C. (2013).
habitual caffeine intake of participants. Accurate determination of Effects of caffeine and carbohydrate mouth rinses on repeated sprint
habitual caffeine intake is difficult due to the high variability of performance. Applied Physiology, Nutrition and Metabolism, 38(6),
caffeine content present in foods and beverages (i.e., coffee, tea, 633–637. doi:10.1139/apnm-2012-0333
mate, and cocoa) (Heckman et al., 2010). Gonçalves et al. (2017) Best, R., McDonald, K., Hurst, P., & Pickering, C. (2020). Can taste be
showed no influence of habituation (low, 58 ± 29 mg/day; moder- ergogenic? European Journal of Nutrition, 0123456789.
ate, 143 ± 25 mg/day; high, 351 ± 139 mg/day intakes) on caf- Betts, J.A., Gonzalez, J.T., Burke, L.M., Close, G.L., Garthe, I., &
feine’s ergogenic effect during ∼30 min TT cycling, while others James, L.J. (2020). PRESENT 2020: Text expanding on the check-
have shown that habitual consumption might attenuate the size of list for proper reporting of evidence in sport and exercise nutrition
caffeine’s ergogenic effect (Beaumont et al., 2017; Ruiz-Moreno trials. International Journal of Sport Nutrition and Exercise Metab-
et al., 2020). Two studies investigating Caff-MR reported habitual olism, 30(1), 2–13. PubMed ID: 31945740 doi:10.1123/ijsnem.
caffeine consumption (Doering et al., 2014; Pataky et al., 2016), 2019-0326
but none directly assessed the effect of habituation on the effec- Borg, G.A.V. (1982). Psychophysical bases of perceived exertion. Medi-
tiveness of Caff-MR. The true influence of habitual caffeine cine and Science in Sports and Exercise. 14(5):377–81. PubMed ID:
consumption on the effects of caffeine supplementation and 7154893 doi:10.1249/00005768-198205000-00012
Caff-MR remains to be determined (Pickering & Kiely, 2019). Bottoms, L., Hurst, H., Scriven, A., Lynch, F., Bolton, J., Vercoe, L., : : :
Further research is required to determine if habituation of caffeine Sinclair, J. (2014). The effect of caffeine mouth rinse on self-paced
modulates sensitivity to repeated caffeine exposure in the mouth cycling performance. Comparative Exercise Physiology, 10(4), 239–
and therefore impacts the potential ergogenic effect of Caff-MR. 245. doi:10.3920/CEP140015.
In conclusion, a repeated Caff-MR intervention did not im- Chambers, E.S., Bridge, M.W., & Jones, D.A. (2009). Carbohydrate
prove TTE or modify RPE or HR, during endurance capacity sensing in the human mouth: Effects on exercise performance and
cycling in recreationally-trained male cyclists. These findings need brain activity. Journal of Physiology, 587(8), 1779–1794. doi:10.
to be taken with caution due to the small sample size and blinding 1113/jphysiol.2008.164285
ineffectiveness. Future research is warranted to elucidate the Clarke, N.D., Kornilios, E., & Richardson, D.L. (2015). Carbohydrate and
potential effects of Caff-MR on exercise and sports performance. caffeine mouth rinses do not affect maximum strength and muscular
More well-designed studies with larger samples are needed to endurance performance. Journal of Strength and Conditioning
determine the optimal dose and further elucidate the possible Research, 29(10), 2926–2931. PubMed ID: 25785703 doi:10.
mechanisms of action with Caff-MR. 1519/JSC.0000000000000945
Cohen, J. (1988). Statistical power analysis for the behavioral sciences.
New York, NY: Routledge.
Acknowledgments
Conway, J.M., Ingwersen, L.A., & Moshfegh, A.J. (2004). Accuracy of
The authors are grateful to all participants in the research. C.E.G. Reis, G.E. dietary recall using the USDA five-step multiple-pass method in men:
Molina, and B. Saunders helped in the conceptualization and methodology An observational validation study. Journal of the American Dietetic
of this study; L.L. Nabuco and C.E.G. Reis helped in the investigation; L.L. Association, 104(4), 595–603. PubMed ID: 15054345 doi:10.1016/j.
Nabuco, R.A.S. Silva, and C.E.G. Reis formally analyzed the study; L.L. jada.2004.01.007
Nabuco and C.E.G. Reis wrote the original draft; B. Saunders, R.A.S. Silva, Cotshall, R.W., Bauer, T.A., & Fahrner, S.L. (1996). Cycling cadence
and G.E. Molina reviewed and edited the manuscript; and C.E.G. Reis alters exercise hemodynamics. Intenational Journal of Sports Medi-
assisted with the resources and supervision. All authors approved the final cine, 17(1), 17–21.
version of the paper. Farmacotécnica Instituto de Manipulações farmacêu- Doering, T.M., Fell, J.W., Leveritt, M.D., Desbrow, B., & Shing, C.M.
ticas LTDA provided anhydrous caffeine. L.L. Nabuco was financially (2014). The effect of a caffeinated mouth-rinse on endurance cycling
supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Super- time-trial performance. International Journal of Sport Nutrition and
ior (CAPES). B. Saunders has been financially supported by Fundação de Exercise Metabolism, 24(1), 90–97. PubMed ID: 23980239 doi:10.
Amparo à Pesquisa do Estado de São Paulo (2016/50438-0) and has also 1123/ijsnem.2013-0103
received a grant from Faculdade de Medicina da Universidade de São Paulo Dolan, P., Witherbee, K.E., Peterson, K.M., & Kerksick, C.M. (2017).
(2020.1.362.5.2). The trial was registered on the Brazilian Registry of Effect of carbohydrate, caffeine, and carbohydrate + caffeine mouth
Clinical Trials (ReBEC) under registration number RBR-65dynt: http:// rinsing on intermittent running performance in collegiate male
www.ensaiosclinicos.gov.br/rg/RBR-65dynt/. lacrosse athletes. Journal of Strength and Conditioning Research,
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTC418 Nabuco et al.
31(9), 2473–2479. PubMed ID: 28825605 doi:10.1519/JSC. Medicine and Physical Fitness, 60(1), 69–74. PubMed ID: 31640317
0000000000001819 doi:10.23736/S0022-4707.19.09928-6
Ehlert, A.M., Twiddy, H.M., & Wilson, P.B. (2020). The effects of Maughan, R.J., Burke, L.M., Dvorak, J., Larson-Meyer, D.E., Peeling, P.,
caffeine mouth rinsing on exercise performance: A systematic review. Phillips, S.M., : : : Engebretsen, L. (2018). IOC consensus statement:
International Journal of Sport Nutrition and Exercise Metabolism, Dietary supplements and the high-performance athlete. British Jour-
30, 1–12. nal of Sports Medicine, 52(7), 439–455. PubMed ID: 29540367
Gibson, R.S. (2005). Principles of nutritional assesment (2nd ed.). Oxford doi:10.1136/bjsports-2018-099027
University Press. Matsumoto, I. (2013). Gustatory neural pathways revealed by genetic
Gilgen-Ammann, R., Schweizer, T., & Wyss, T. (2019). RR interval tracing from taste receptor cells. Bioscience, Biotechnology and
signal quality of a heart rate monitor and an ECG Holter at rest and Biochemistry, 77(7), 1359–1362. doi:10.1271/bbb.130117
during exercise. European Journal of Applied Physiology, 119(7), Meeusen, R., Roelands, B., & Spriet, L.L. (2013). Caffeine, exercise and
1525–1532. PubMed ID: 31004219 doi:10.1007/s00421-019- the brain. Nestle Nutrition Institute Workshop Series, 76, 1–12.
04142-5 PubMed ID: 23899750
Gonçalves, L.de S., Painedly, V.de S., Yamaguchi, G., Oliveira, L.F.de, Pataky, M.W., Womack, C.J., Saunders, M.J., Goffe, J.L., D’Lugos, A.C.,
Saunders, B., da Silva, R.P., : : : Gualano, B. (2017). Dispelling the El-Sohemy, A., & Luden, N.D. (2016). Caffeine and 3-km cycling
myth that habitual caffeine consumption influences the performance performance: Effects of mouth rinsing, genotype, and time of day.
response to acute caffeine supplementation. Journal of Applied Scandinavian Journal of Medicine and Science in Sports, 26(6), 613–
Physiology, 123(1), 213–220. doi:10.1152/japplphysiol.00260. 619. PubMed ID: 26062916 doi:10.1111/sms.12501
2017 Pauw, K., Roelands, B., Cheung, S.S., de Geus, B., Rietjens, G., &
Grgic, J., Grgic, I., Pickering, C., Schoenfeld, B.J., Bishop, D.J., & Meeusen, R. (2013). Guidelines to Classify Subject Groups in
Pedisic, Z. (2020). Wake up and smell the coffee: Caffeine sup- Sport-Science Research. International Journal of Sports Physiology
plementation and exercise performance—An umbrella review of 21 and Performance, 8(2), 111–122. PubMed ID: 23428482 doi:10.
published meta-analyses. British Journal of Sports Medicine, 1123/ijspp.8.2.111
54(11), 681–688. PubMed ID: 30926628 doi:10.1136/bjsports- Pickering, C. (2019). Are caffeine’s performance-enhancing effects par-
2018-100278 tially driven by its bitter taste? Medical Hypotheses, 131, 109301.
Guest, N., VanDusseldorp, T., Nelson, M., Grgic, J., Schoenfeld, B.J., PubMed ID: 31443771 doi:10.1016/j.mehy.2019.109301
Jenkins, N., : : : Trexler, E.T. (2021). International society of sports Pickering, C., & Kiely, J. (2019). What should we do about habitual
nutrition position stand: caffeine and exercise performance. Journal caffeine use in athletes? Sports Medicine, 49(6), 833–842. PubMed
of the International Society of Sports Nutrition, 18(1), 1. doi:10.1186/ ID: 30173351 doi:10.1007/s40279-018-0980-7
s12970-020-00383-4 Poole, R.L., & Tordoff, M.G. (2017). The taste of caffeine. Journal of
Hawley, J.a.& Noakes, T.D. (1992). Peak power output predicts maximal Caffeine Research, 7(2), 39–52. PubMed ID: 28660093 doi:10.1089/
oxygen uptake and performance time in trained cyclists. European jcr.2016.0030
Journal of Applied Physiology, 65(1), 79–83. doi:10.1007/ Ribeiro, J.A., & Sebastio, A.M. (2010). Caffeine and adenosine. Journal of
BF01466278 Alzheimer’s Disease, 20(Suppl. 1), S3–S15.
Heckman, M., Weil, J., & De Meija, E.G. (2010). Caffeine (1, 3, 7- Rubinstein, I., Chandilawa, R., Dagar, S., Hong, D., & Gao, X.P. (2001).
trimethylxanthine) in Foods: A Comprehensive review on consump- Adenosine A1 receptors mediate plasma exudation from the oral
tion, functionality, safety, and regulatory matters. Journal of Food mucosa. Journal of Applied Physiology, 91(2), 552–560. PubMed ID:
Science, 75(3), R77–R87. PubMed ID: 20492310 doi:10.1111/j. 11457765 doi:10.1152/jappl.2001.91.2.552
1750-3841.2010.01561.x Ruiz-Moreno, C., Lara, B., Salinero, J.J., Brito de Souza, D., Ordovás,
Kalmar, J.M., & Cafarelli, E. (1999). Effects of caffeine on neuromuscular J.M., & Del Coso, J. (2020). Time course of tolerance to adverse
function. Journal of Applied Physiology, 87(2), 801–808. PubMed effects associated with the ingestion of a moderate dose of caffeine.
ID: 10444642 doi:10.1152/jappl.1999.87.2.801 European Journal of Nutrition, 0123456789.
Kamimori, G.H., Karyekar, C.S., Otterstetter, R., Cox, D.S., Balkin, T.J., Saunders, B., de Oliveira, L.F., da Silva, R.P., de Salles Painelli, V.,
Belenky, G.L., & Eddington, N.D. (2002). The rate of absorption and Gonçalves, L.S., Yamaguchi, G., : : : Gualano, B. (2017). Placebo in
relative bioavailability of caffeine administered in chewing gum sports nutrition: a proof-of-principle study involving caffeine sup-
versus capsules to normal healthy volunteers. International Journal plementation. Scandinavian Journal of Medicine and Science in
of Pharmaceutics, 234(1–2), 159–167. PubMed ID: 11839447 Sports, 27(11), 1240–1247. PubMed ID: 27882605 doi:10.1111/
doi:10.1016/S0378-5173(01)00958-9 sms.12793
Kizzi, J., Sum, A., Houston, F.E., & Hayes, L.D. (2016). Influence of a Saunders, B., Saito, T., Klosterhoff, R., De Oliveira, L. F., Barreto, G.,
caffeine mouth rinse on sprint cycling following glycogen depletion. Perim, P., : : : Gualano, B. (2019). I put it in my head that the
European Journal of Sport Science, 16(8), 1087–1094. PubMed ID: supplement would help me”: Open-placebo improves exercise per-
27686403 doi:10.1080/17461391.2016.1165739 formance in female cyclists. PLoS One, 14(9), e0222982–16. doi:10.
Kuipers, H., Verstappen, F.T.J., Keizer, H.A., Geurten, P., & van 1371/journal.pone.0222982
Kranenburg, G. (1985). Variability of aerobic performance in Shen, J.G., Brooks, M.B., Cincotta, J., & Manjourides, J.D. (2019).
the laboratory and its physiologic correlates. International Journal Establishing a relationship between the effect of caffeine and
of Sports Medicine, 6(4), 197–201. PubMed ID: 4044103 doi:10. duration of endurance athletic time trial events: A systematic review
1055/s-2008-1025839 and meta-analysis. Journal of Science and Medicine in Sport,
Landrum, R.E. (1992). College student’s use of caffeine and its relation- 22(2), 232–238. PubMed ID: 30170953 doi:10.1016/j.jsams.2018.
ship to personality. College Student Journal, 26(2), 151–155. 07.022
Marinho, A.H., Mendes, E.V., Vilela, R.A., Bastos-Silva, V.J., Araujo, Sinclair, J., & Bottoms, L. (2014). The effects of carbohydrate and caffeine
G.G., & Balikian, P. (2020). Caffeine mouth rinse has no effects on mouth rinsing on arm crank time-trial performance. Journal of Sports
anaerobic energy yield during a Wingate Test. The Journal of Sports Research, 1(2), 34–44.
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTCCaffeine Mouth Rinse and Cycling to Exhaustion Performance 419
Southward, K., Rutherfurd-Markwick, K.J., & Ali, A. (2018). The effect of World Health Organization. (2020). Body mass index—BMI. Retrieved
acute caffeine ingestion on endurance performance: A systematic from https://www.euro.who.int/en/health-topics/disease-prevention/
review and meta-analysis. Sports Medicine, 48(8), 1913–1928. nutrition/a-healthy-lifestyle/body-mass-index-bmi
PubMed ID: 29876876 doi:10.1007/s40279-018-0939-8 Zald, D.H., Hagen, M.C., & Pardo, J.V. (2002). Neural correlates of tasting
Wickham, K.A., & Spriet, L.L. (2018). Administration of caffeine in concentrated quinine and sugar solutions. Journal of Neurophysiol-
alternate forms. Sports Medicine, 48, 79–91. PubMed ID: 29368182 ogy, 87(2), 1068–1075. PubMed ID: 11826070 doi:10.1152/jn.
doi:10.1007/s40279-017-0848-2 00358.2001
IJSNEM Vol. 31, No. 5, 2021
Brought to you by IJSNEM Board Membership (1/2) | Authenticated jb335@bath.ac.uk | Downloaded 08/16/21 08:22 AM UTCYou can also read
