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Original Research

Effect of Carbohydrate, Caffeine, and Carbohydrate + Caffeine Mouth Rinsing on Intermittent Running Performance in Collegiate Male Lacrosse Athletes

Dolan, Patrick1; Witherbee, Kyle E.2; Peterson, Kimi M.2; Kerksick, Chad M.2

Author Information
Journal of Strength and Conditioning Research: September 2017 - Volume 31 - Issue 9 - p 2473-2479
doi: 10.1519/JSC.0000000000001819
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Abstract

Introduction

The impact of ingesting carbohydrate to impact both aerobic and anaerobic performance is one of the most well-documented nutritional strategies to mitigate a wide array of physical performance (5,6). In 2004, Carter et al. (7) first illustrated that rinsing the oral cavity with a 6.4% maltodextrin solution at regular intervals throughout a 1-hour bout of cycling significantly increased average power output when compared with a placebo. Later, in 2008, Rollo et al. (25) had study participants rinse with a carbohydrate solution (CHO) before completing a 30-minute treadmill run at a self-selected intensity and found that a greater total distance was covered after mouth rinsing with carbohydrate. Since then, multiple investigations have examined the impact of carbohydrate mouth rinsing on continuous intensity, aerobic-type exercise ranging from 30 minutes to 2 hours (7,24–26), and most recently during repeated 6-second bouts of maximal sprint cycling (4) and while completing high-intensity interval running in a carbohydrate-restricted state (17).

Beginning in 2013, mouth rinsing with a caffeine solution was first investigated for its ability to impact exercise performance. Caffeine is well known for its ability to positively impact various types of exercise performance and perceptions of physical work (12,13). This initial work by Beaven required 12 trained men to complete five 6-second maximal sprints on a cycle ergometer with 24 seconds of rest between each sprint repetition. The authors found that a 1.2% caffeine solution (CAF) significantly increased mean power production during the first and second sprints when compared with a placebo. In addition, they reported that a combination of 6% carbohydrate and 1.2% caffeine significantly increased peak power production during the first sprint when compared with performance in the carbohydrate-only condition (4). Since that time, 3 studies have been published with mixed results that have examined mouth rinsing with caffeine. Kizzi et al. (18) concluded that caffeine mouth rinsing improved sprint cycling when glycogen depleted in a group of recreationally active men, whereas Doering et al. (9) concluded in 2014 that multiple doses of a caffeine mouth rinse had no impact over cycling time-trial performance. Finally, Clarke et al. (8) were the first to examine all combinations of carbohydrate and caffeine mouth rinsing and found no impact of the strategy on maximal strength and muscular endurance.

Notably, none of the discussed literature has examined the impact of caffeine mouth rinsing using a performance test that is directly applicable to the hundreds of thousands of athletes performing intermittent, high-intensity activity such as basketball, lacrosse, field hockey, and soccer. These sports comprised repeated transitions of all exercise intensities that effectively challenge all metabolic systems for the duration of competition (1,19,20,22). Surprisingly, only 1 published study to date has investigated the effects of carbohydrate mouth rinsing on intermittent running performance outside of a laboratory setting. In this study, Dorling and Earnest had 8 young active men complete the Loughborough Intermittent Shuttle Test (LIST) with and without mouth rinsing a 6.4% CHO before completing the exercise tests. No difference in average or fastest sprint times and no differences in rating of their perceived exertion (RPE) or glucose concentrations were found (10).

The purpose of this study is to determine the independent and synergistic impact of mouth rinsing with a CHO and caffeine solution on intermittent running performance in competitive lacrosse athletes using the Yo-Yo Intermittent Recovery Test-Level 1 (Yo-Yo IRT-1). The Yo-Yo IRT-1 has been specifically developed to mimic the high-intensity running bouts in football (soccer) match play (2) and to assess an athlete's fatigue resistance during intermittent exercise, taxing both the aerobic and anaerobic energy systems (19). This test has high reproducibility, operates with a high level of ecological validity, and is sensitive to changes in fitness status as well as the competition level of team sport players (15,19,21), training interventions (14,22), and nutritionally mediated improvements in performance (28). This study is significant as it examines for the first time a nutritional concept that has yet to be studied in trained, competing athletes who perform high-intensity, intermittent exercise. Outcomes related to this study will better inform coaches and athletes about the efficacy of strategic implementation of nutrient mouth rinsing at opportune times throughout various forms of competition.

Methods

Experimental Approach to the Problem

The subjects reported to the indoor training facility on 5 separate occasions over a 29-day period. On providing consent, all participants were first provided a verbal explanation of the Yo-Yo IRT-1 before completing an informal walkthrough (19). On visit 1, subjects completed the first of 5 Yo-Yo IRT-1 tests, which served as a familiarization trial. All testing was completed during the competitive season during the months of February and March on the same day each week to avoid deviations in team travel and deviations in training load preceding each test. All tests were completed in the morning hours (0630–0900) after observing an overnight fast. Each participant was assigned to a cohort interspersed by 30-minute intervals (starting at 0630), and all participants completed all tests each week at this assigned time. Subjects were asked to record their food intake in the 24 hours preceding the first experimental trial and to replicate this same diet in the 24 hours preceding the subsequent trials. Subjects were instructed to arrive at the laboratory 15 minutes before their scheduled testing time in a rested and fully hydrated state after observing an overnight fast (∼10 hours), and to avoid strenuous exercise in the 12 hours preceding each experimental trial. Each week, all cohorts were led though an identical warm-up by their strength and conditioning coach before completing the Yo-Yo IRT-1. Subjects were then assigned in a double-blind, randomized crossover design to receive 1 of 5 conditions on the following 4 testing days: 6% CHO, CAF, 6% CHO + 1.2% CAF solution (CHO + CAF), flavored water to taste identical to other rinsing condition solutions, which subsequently served as a placebo (H2O), or a no rinse control (CON) condition. Each participant was provided 25 ml of their assigned solution and instructed to rinse their entire oral cavity for 10 seconds and spit the rinse into a nearby waste receptacle. Each week, the Yo-Yo IRT-1 began immediately after completing the mouth rinsing protocol.

Subjects

Fourteen male, NCAA Division II competitive lacrosse players (19.9 ± 1.3 years, 182 ± 9 cm, 84.9 ± 15.7 kg, 11.3 ± 3.8% fat) volunteered to participate in this study. All assessments were completed in-season, and all participants were familiar with intense intermittent exercise. Subjects gave their written informed consent to participate after the experimental procedures, associated risks, and potential benefits of participation had been explained in detail. The study was approved by an accredited IRB committee (IntegReview, approval date: February 6, 2015) and in accordance with the Declaration of Helsinki.

Procedures

Mouth Rinsing Protocol

In a randomized, double-blind, placebo-controlled manner, each study participant was assigned each week to 1 of 5 experimental conditions. The 5 conditions were 6% carbohydrate, 1.2% caffeine, 6% carbohydrate + 1.2% caffeine, flavored water, and a CON. Each week a total solution of 150 ml was prepared by the same study investigator using graduated cylinders, electronic laboratory scales, calibrated micropipetting devices, and distilled water at room temperature. A separate, nonstudy investigator appropriately labeled all the conditions, effectively blinding all study investigators and participants to each condition. To mask flavor and create consistencies from one group to the next, each solution had 2 packets of sucralose included along with 1 teaspoon of a nonsugar, cherry flavored sweetener. Powdered sources of dextrose and caffeine from Sigma chemicals (St. Louis, MO) were each used in the preparation of all solutions. Each week, 25 ml of each condition was pipetted into a small reservoir where participants were instructed to rinse their entire oral cavity for a total of 10 seconds (27) before expectorating the solution into a nearby waste receptacle. Study investigators were present during all rinse protocols and visually observed each participant after the protocol. When assigned to the CON, participants waited the entire 10-second period before beginning the Yo-Yo IRT-1 test. Promptly after completion of all rinse protocols, study participants began the Yo-Yo IRT-1.

Yo-Yo Intermittent Recovery Test-Level 1

The Yo-Yo IRT-1 test was performed indoors in a controlled, thermoneutral environment on a turf surface in running lanes with a width of 1.5 m and a length of 20 m. The Yo-Yo IRT-1 test has been described and evaluated previously (2,19). In brief, it consists of two 20-m runs (down and back) at progressively increasing speeds, controlled by auditory cues from an overhead speaker. Each running bout was interspersed by a 10-second active recovery period where the subject walks or jogs around a marker placed 5 m behind the starting line (3). Because of facility restrictions, this study was able to use only a 4-m marker for the active recovery, but the entire 20-m running distance was provided and was measured each week by study investigators. Participants were allowed 2 fails before the test was considered complete and the distance recorded. A fail was indicated by a researcher if any participant failed to traverse the initial 20 m leg of the test or change direction and reach the finishing line in time. To ensure accurate administration of the testing protocol, group sizes were limited to no more than 5 athletes. The same 2 investigators were responsible for the start line and 20 m change of direction line for each subsequent trial. Intraclass correlations were computed using all conditions for all participants (ICC r = 0.751; 95% CI: 0.544–0.898).

Rating of Perceived Exertion

Subjects were asked to give an RPE based on Borg's scale of 6–20 immediately after their warm-up, and after the first sprint bout of each new speed level. A final RPE was also indicated immediately after the subject was terminated from the test.

Statistical Analyses

After randomization, 4 participants of the original 14 participants failed to complete all required testing. Two participants were lost because of musculoskeletal injuries sustained during competition, another became ill, and another was absent due to a personal obligation. Because of logistical limitations within the competitive season, each participant completed 4 of the 5 experimental conditions resulting in a sample size of 10 participants (n = 10) for each condition. Statistical power analysis completed using data from Bailey et al. (2013) revealed a required sample size of 10 participants at an alpha value of 0.05 and a power of 0.812. Normality of all data was confirmed using visual inspection of skewness and kurtosis scores and Shapiro-Wilk statistics. One-way ANOVA was used to determine the impact of each mouth rinse condition on running performance. When significant, Tukey's post-hoc procedures were used to identify the significance between individual groups. In addition, RPE data were rank transformed and then analyzed using a 5 × 8 (group × time) mixed factorial ANOVA. Level 17 and peak RPE were not included in this analysis because level 17 data had too few data points, and peak RPE exhibited near identical scores across all conditions. Intraclass correlation coefficients were computed for all conditions of all participants of the Yo-Yo and was reported to be ICC r = 0.751 with a 95% confidence interval of 0.544–0.898. All data are presented as mean ± SD. A probability value (p-value) of 0.05 was used to determine the presence of statistical significance.

Results

Familiarization and Session Effect

Using a factorial ANOVA with repeated measures, meters completed by all study participants were significantly less after the familiarization trial (week 1: 1,206 ± 280 m) in comparison with week 2 (1,300 ± 277 m, p = 0.02), week 3 (1,374 ± 304 m, p = 0.001), week 4 (1,403 ± 370 m, p = 0.01), and week 5 (1,400 ± 318 m, p = 0.004). Notably, no other significant differences (p > 0.05) were found between Yo-Yo IRT-1 performances between weeks 2–5.

Yo-Yo Intermittent Recovery Test-Level 1 Performance

Using 1-way ANOVA, no significant between-group differences were found for the meters completed by any of the 5 experimental conditions (CHO = 1,480 ± 253; H2O = 1,397 ± 360; CHO + CAF = 1,229 ± 302; CAF = 1,342 ± 320; CON = 1,436 ± 292 m, p = 0.40) during the Yo-Yo IRT-1 (Figures 1 and 2). Subsequently, no significant between-group differences (p = 0.40) were found in the level completed by any of the 5 experimental conditions (Table 1).

Figure 1.
Figure 1.:
Meters completed during the Yo-Yo intermittent recovery test-level 1. Data are presented as mean ± SD. All groups rinsed a 25-ml solution for 10 seconds in a double-blind, placebo-controlled manner. Fourteen participants completed 5 identical trials in consecutive weeks consisting first of a familiarization and then randomly completed 4 of the 5 conditions resulting in a sample size of 10 participants in each condition. CHO = 6% carbohydrate solution; H2O = flavored water; CAF = 1.2% caffeine solution; CHO + CAF (6% carbohydrate + 1.2% caffeine solution); CON = no rinse control. The vertical dashed line is placed at the average meters completed for all study participants for all completed trials (1,374 ± 310 m, n = 50).
Figure 2.
Figure 2.:
Individual responses of meters completed during the Yo-Yo intermittent recovery test-level 1 for all study participants across all conditions. Data are presented as mean ± SD. All groups rinsed a 25-ml solution for 10 seconds in a double-blind, placebo-controlled manner. Fourteen participants completed 5 identical trials in consecutive weeks consisting first of a familiarization and then randomly completed 4 of the 5 conditions resulting in a sample size of 10 participants in each condition. CHO = 6% carbohydrate solution; H2O = flavored water; CAF = 1.2% caffeine solution; CHO + CAF (6% carbohydrate + 1.2% caffeine solution), CON = no rinse control. The solid black horizontal line within each condition is placed at the average meters completed for all study participants for each respective condition.
Table 1.
Table 1.:
Yo-Yo Intermittent Recovery Test-Level 1 running level.*†‡§

Rating of Perceived Exertion

Rating of their perceived exertion data were collected after the completion of each level of the Yo-Yo IRT-1 performance test (Table 2). Univariate ANOVA completed on each level revealed that RPE values after level 11 were found to be significantly different (p = 0.03) among the groups. Tukey's post-hoc follow-up tests revealed that RPE values for the 6% CHO were significantly less than the RPE values reported during the flavored water (H2O) group with no other differences being realized; notably, the other carbohydrate-containing group (CHO + CAF) exhibited the second lowest mean RPE score at this time point. No other between-group differences were found among the RPE data (Table 2). Interestingly, visual inspection of RPE data revealed that RPE data for CHO was lower than all other groups after all levels of the Yo-Yo IRT-1 with the exception of level 16, where CHO was the second lowest RPE score. To investigate this observation, a rank transformation was completed of all RPE data with the exception of level 17 and peak RPE before being analyzed using ANOVA. Regardless, no significant group x time interaction was found (p = 0.21).

Table 2.
Table 2.:
Ratings of perceived exertion at each level completed of the Yo-Yo Intermittent Recovery Test-Level 1.*†

Discussion

A priority of this investigation was to examine the potential impact of mouth rinsing with either carbohydrate or caffeine using a test that had high transfer and ecological validity for team sport athletes and their coaches. Of the growing body of literature, only 1 study has examined the efficacy of mouth rinsing with carbohydrate outside of a laboratory setting, and no study at the current time has used an ecologically valid, field-based approach examining caffeine mouth rinsing. The exercise test used in this study, the Yo-Yo IRT-1, is a validated, intermittent running test that takes place out of a laboratory setting and has been successfully used to tax and assess the activation and interaction of all 3 energy systems (2,19). The results of the study showed that mouth rinsing for 10 seconds with a 6% CHO, CAF, or a combined solution (6% carbohydrate + 1.2% caffeine) did not significantly change the total distance completed during the Yo-Yo IRT-1. When compared with flavored water and independent of caffeine, RPEs were significantly reduced when carbohydrate was provided (6% CHO and 6% CHO + CAF) after completion of level 11 of the Yo-Yo IRT-1, whereas mean RPE values were lower (nonsignificantly) in the carbohydrate group than all other groups in all but one level of the Yo-Yo IRT-1.

In concert with these findings, other studies examining the impact of mouth rinsing have also reported nonsignificant outcomes. For example, Rollo et al. in 2011 found that in 10 endurance trained runners, there was no significant impact on a 60-minute run for distance with a CHO solution rinse compared with the placebo. Alternatively, when carbohydrate was ingested at the same time intervals throughout an identical 60-minute run, CHO ingestion led to a significantly greater distance being covered (∼230 m) when compared with the rinse condition (26). In 2013, Dorling et al. published results from a study in 8 active men who were required to complete multiple running sprints (the LIST). Similar to this study, performance and perceived rate of exertion were not improved as a result of carbohydrate mouth rinsing (10). This study is significant because it remains as the only the study that has examined any form of nutrient mouth rinsing using a nonlaboratory, field-based assessment.

Previous work by Rollo in 2008 has speculated that the brain or laminal spinothalamocoritical system might be responsible for monitoring the status of muscle or carbohydrate stores throughout the body (Rollo, 2008). Their findings of initial improvements in perceptual feelings of readiness are consistent with findings from this study that indicated reduced perceptions of effort early in the performance of the intermittent running test. In this study, they reported improvements in perceptual reports during the first 5 minutes of their exercise bout (Rollo, 2008), whereas RPE values in this study were consistently lower in the carbohydrate group when compared with all other conditions in all but one level of the Yo-Yo run test. In addition, and as also stated by Rollo et al., it was speculated that the “promise” of additional carbohydrate might heighten activation of this system, but when no additional carbohydrate arrives, perceptual indicators are adjusted. This is an attractive hypothesis that remains to be fully investigated, particularly as it applies across all types of physical exercise bouts and protocols. To this point, it is important to mention that our study protocol provided only 1 rinse for an exercise stress that spanned 12–16 minutes. In comparison, the study protocol of Carter (7) provided an equivalent rinse every 12.5% of completion of what approximated to be a 1-hour cycling trial or every 7.5 minutes. Thus, it is possible that more regular exposure (i.e., a second or third dose in our protocol) might have been needed to appropriately stimulate the oral cavity receptors; however, the results of Dorling refute this assertion (10).

The inclusion of caffeine was a novel aspect of our study design with much less work having been completed using caffeine (4,8,9,18). Briefly, caffeine ingestion is well documented to favorably impact different types of physical performance (11), and caffeine is believed to act by activation of central nervous system components (e.g., motor unit activation) and adenosine receptor antagonism (11,16). Consistent with the hypothesis of oral cavity receptor activation triggering the observed ergogenic outcomes for carbohydrate, Paton et al. (23) provided cyclists with caffeinated gum and observed an improvement in repeated sprint performance ability. Beaven et al. had 12 men rinse their oral cavity for 5 seconds before each of five 6-second sprints that were completed on a cycle ergometer. These authors concluded that caffeine rinsing improved average power throughout the first of 6 sprints. In addition, the combination of caffeine and carbohydrate was also found to significantly improve power production during the first sprint (4). Clarke et al., using an excellent study design, examined the individual and combined effects of carbohydrate and caffeine mouth rinsing on 1 repetition maximum (1RM) and muscular endurance performance. These authors concluded that neither protocol was able to significantly impact maximal strength or repetitions completed (8). Kizzi (18), in 2016, also showed a benefit of caffeine mouth rinsing during sprint cycling when participants were carbohydrate-challenged, whereas Doering et al. (9) reported no impact on cycling time-trial performance. Overall, it is challenging to directly compare outcomes between this study and all previous findings, as this study remains as the only investigation to examine caffeine mouth rinsing using a nonlaboratory-based approach. As it stands, much more work is needed to fully examine the potential impact of caffeine rinsing before exercise performance, although results from this study indicate that caffeine rinsing alone or in combination with carbohydrate may not impact intermittent running performance in trained collegiate athletes.

The strengths of our study include our randomized, double-blind, crossover design with both a CON and flavored water conditions. To date, only one other study has used that study approach (8). In addition, the selection of a previously validated intermittent running test that has been shown to accurately predict V̇o2max of soccer athletes (2,19) and identify treatment outcomes associated with nitrate administration (28) in running athletes heightens the ecological validity for our study protocol. Moreover, to the best of our knowledge, the findings from our study provide the first data examining the impact of caffeine alone or in combination with carbohydrate when completing any form of performance assessment outside of a laboratory setting.

Our study is limited by our relatively low sample size, even though a power analysis that used the findings presented by Wylie in 2013, where they reported a significant improvement in Yo-Yo IRT-1 performance after nitrate supplementation, indicated a sample size of 10 participants would yield a power of 0.812. Therefore, the lower sensitivity of a field-based approach in combination with smaller effects may have underpinned our ability to identify an impact. Furthermore, the reach of our study could have been greater by examining changes in heart rate, glucose, or lactate. In this respect, current evidence indicates very little impact on these markers after mouth rinsing, and our study was focused exclusively on perceptual changes and running performance. In conclusion, results from this study indicate that running performance of trained collegiate athletes in the Yo-Yo IRT-1 was not significantly impacted by following a 10-second mouth rinse of the oral cavity with a 6% carbohydrate, 1.2% caffeine, or a combination of 6% carbohydrate + 1.2% caffeine when compared with similarly flavored water or a CON.

Practical Applications

Results from this study directly inform coaches and athletes on the potential impact of mouth rinsing with carbohydrate and caffeine on intermittent running performance. Although valuable, outcomes from previous studies have lacked ecological validity to coaches and athletes because of nearly all previous studies being published in laboratory settings. Like the Dorling paper, this study used a validated intermittent running test that closely replicates the physical and mental challenges experienced by the thousands of athletes participating in sports that involve intermittent, high-intensity running, and this study was the first to explore the impact of caffeine mouth rinsing to impact high-intensity running performance.

It is critical to consider that from a strategic perspective, mouth rinsing with nutrients, and in particular caffeine at opportune times, may facilitate heightened physical and mental performance. Furthermore, athletes, who are sensitive to the volume of fluid in their stomach, use a nutrient that has published legislation by athletic governing bodies (i.e., NCAA) or need a boost at a key moment during competition (e.g., penalty kicks, overtime, time-outs, etc.); the potential for mouth rinsing to increase performance is intriguing. Finally, it should not be overlooked that our results should reinforce to coaches and athletes the positive impact of ingesting nutrients such as carbohydrates and caffeine throughout competition.

Acknowledgments

The authors are indebted to the athletes and coaches who were so supportive of data collection throughout what amounted to be a time-demanding, but quite successful competitive season. In addition, the authors also gratefully acknowledge the support from Lindenwood University administration to provide the necessary funds for external IRB review to facilitate timely review of this study. The authors disclose that they have no conflicts of interest related to this study's content. Furthermore, publication of these results does not constitute endorsement by the authors or the NSCA or the institutions where the authors are affiliated.

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Keywords:

ecological validity; sports nutrition; practical; assessments

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