Carbohydrate mouth rinse failed to reduce central fatigue, lower perceived exertion, and improve performance during incremental exercise

We examined if carbohydrate (CHO) mouth rinse may reduce central fatigue and perceived exertion, thus improving maximal incremental test (MIT) performance. Nine recreational cyclists warmed up for 6 min before rinsing a carbohydrate (CHO) or placebo (PLA) solution in their mouth for 10 s in a double-blind, counterbalanced manner. Thereafter, they performed the MIT (25 W·min-1 increases until exhaustion) while cardiopulmonary and ratings of perceived exertion (RPE) responses were obtained. Pre- to post-MIT alterations in voluntary activation (VA) and peak twitch torque (Tw) were determined. Time-to-exhaustion (p = 0.24), peak power output (PPO; p = 0.45), and V̇O2MAX (p = 0.60) were comparable between conditions. Neither treatment main effect nor time-treatment interaction effect were observed in the first and second ventilatory threshold when expressed as absolute or relative V̇O2 (p = 0.78 and p = 0.96, respectively) and power output (p = 0.28 and p = 0.45, respectively) values, although with moderate-to-large effect sizes. RPE increased similarly throughout the tests and was comparable at the ventilatory thresholds (p = 0.56). Despite the time main effect revealing an MIT-induced central and peripheral fatigue as indicated by the reduced VA and Tw, CHO mouth rinse was ineffective in attenuating both fatigues. Hence, rinsing the mouth with CHO was ineffective in reducing central fatigue, lowering RPE, and improving MIT performance expressed as PPO and time-to-exhaustion. However, moderate-to-large effect sizes in power output values at VT1 and VT2 may suggest some beneficial CHO mouth rinse effects on these MIT outcomes.

Carbohydrate Oral Rinsing, Cycling Performance and Individual Complex Carbohydrate Taste Sensitivity

The aim of this pilot study was to determine the effect of individual complex carbohydrate taste sensitivity on cycling performance with complex carbohydrate oral rinsing. Ten male participants completed five cycling time trials in a fasted state with a seven-day washout period between each trial. Participants completed a fixed amount of work (738.45 ± 150.74 kJ) as fast as possible on a cycle ergometer while rinsing with an oral rinse for 10 s every 12.5% of the trial. An oral rinse (maltodextrin, oligofructose, glucose, sucralose or water control) was given per visit in a randomised, crossover, blinded design. Afterwards, participants had their taste assessed with three stimuli, complex carbohydrate (maltodextrin), sweet (glucose) and sour (citric acid), using taste assessment protocol to determine individual taste sensitivity status. Participants were subsequently grouped according to their complex carbohydrate taste sensitivity and complex carbohydrate taste intensity. There were no significant effects of the oral rinses on cycling performance time (p = 0.173). Participants who did not have improvements in exercise performance with the maltodextrin rinse experienced a stronger taste intensity with complex carbohydrate stimuli at baseline (p = 0.047) and overall (p = 0.047) than those who did have improvements in performance. Overall, a carbohydrate oral rinse was ineffective in significantly improving cycling performance in comparison with a water control. However, when participants were grouped according to complex carbohydrate taste intensity, differences in exercise performance suggest that individual sensitivity status to complex carbohydrates could impact the efficacy of a carbohydrate-based oral rinse.

Central effects of mouth rinses on endurance and strength performance

Rinsing the mouth with a carbohydrate (CHO) solution has been shown to enhance exercise performance while reducing neuromuscular fatigue. This effect is thought to be mediated through the stimulation of oral receptors, which activate brain areas associated with reward, motivation, and motor control. Consequently, corticomotor responsiveness is increased, leading to sustained levels of neuromuscular activity prior to fatigue. In the context of endurance performance, the evidence regarding the central involvement of mouth rinse (MR) in performance improvement is not conclusive. Peripheral mechanisms should not be disregarded, particularly considering factors such as low exercise volume, the participant's fasting state, and the frequency of rinsing. These factors may influence central activations. On the other hand, for strength-related activities, changes in motor evoked potential (MEP) and electromyography (EMG) have been observed, indicating increased corticospinal responsiveness and neuromuscular drive during isometric and isokinetic contractions in both fresh and fatigued muscles. However, it is important to note that in many studies, MEP data were not normalised, making it difficult to exclude peripheral contributions. Voluntary activation (VA), another central measure, often exhibits a lack of changes, mainly due to its high variability, particularly in fatigued muscles. Based on the evidence, MR can attenuate neuromuscular fatigue and improve endurance and strength performance via similar underlying mechanisms. However, the evidence supporting central contribution is weak due to the lack of neurophysiological measures, inaccurate data treatment (normalisation), limited generalisation between exercise modes, methodological biases (ignoring peripheral contribution), and high measurement variability.Trial registration: PROSPERO ID: CRD42021261714.

Caffeine Mouth Rinse Plus Ingestion Improves the 10-Km Time Trial Compared to Caffeine Mouth Rinse Alone

Background: The benefits of caffeine to physical performance have been extensively demonstrated, however, it has recently been speculated that there is an effect of the administration route on its effectiveness. Purpose: The current study investigated the effect of caffeine mouth rinse in isolation or combined with ingestion on performance in a 30-minute constant-load exercise followed by a 10-km cycling time trial. Methods: Ten physically active men performed a 30-minute constant-load exercise at 50% of the graded test Wmax, followed by a 10-km cycling time trial. Before and at the middle points of the constant-load exercise and 10-km cycling time trial, the following conditions were administered: PLA (cellulose ingestion plus mouth rinsing with magnesium sulfate), ING (5 mg.kg-1 of caffeine ingestion plus mouth rinsing with magnesium sulfate), MR (cellulose ingestion plus mouth rinsing with 1.2% caffeine), and COMB (5 mg.kg-1 of caffeine ingestion plus mouth rinsing with 1.2% caffeine). Results: During the 30-minute constant-load exercise, COMB presented a lower rating of perceived exertion (RPE) than MR (p = .04). For the 10-km time trial, the COMB was faster than MR (MR = 1363 ± 345 vs. COMB = 1291 ± 308s, Δ% = 5.57, p = .05). Mean power output was higher in COMB than PLA, ING, and MR (234 ± 15 vs. 169 ± 29, 148 ± 11, and 145 ± 12 W, respectively). There were no differences between conditions for heart rate and RPE during the 10-km time trial. Conclusion: In summary, caffeine mouth rinsing potentiated the effects of caffeine ingestion during the 10-km time trial compared to caffeine mouth rinsing alone.

The effect of acute manipulation of carbohydrate availability on high intensity running performance, running economy, critical speed, and substrate metabolism in trained Male runners

Completing selected training sessions with reduced glycogen availability is associated with greater signalling and improved muscle oxidative capacity, although it may impact the overall quality of the session. We examined the effects of low carbohydrate availability on high intensity exercise performance, running economy, critical speed, and substrate metabolism. On two occasions, nine male runners (V̇O2peak 60.3 ± 3.3 mL.kg-1.min-1) completed a glycogen depletion protocol involving 90-min at 75%vV̇O2peak followed by 10 × 1-min at 110% vV̇O2peak. This was followed either by high (HIGH) or low (LOW) carbohydrate intake (>6 g.kg-1.day-1 and <50 g.day-1, respectively) until completion of a performance protocol on day 2 consisting of a series of time-trials (TT) (50m to 3000m) and physiological assessments. There were no differences between LOW and HIGH for any TT distance (mean TT performance times for LOW and HIGH were: 3000m TT 651.7 ± 52.8s and 646.4 ± 52.5s, 1500 m TT 304.0 ± 20.2s and 304.2 ± 22.1s, 400 m TT 67.64 ± 4.2s and 67.3 ± 3.8s, 50 m TT 7.27 ± 0.44s and 7.25 ± 0.45s, respectively, P > 0.05), though some athletes performed better in LOW (n = 5). While fat oxidation in LOW was significantly greater than HIGH (Δ0.32 ± 0.14 g.min-1; P < 0.001 at 14 km.h-1 and Δ0.34 ± 0.12 g.min-1 at 16 km.h-1; P < 0.01), running economy did not differ between trials (P > 0.05). Acute manipulation of carbohydrate availability showed immediate effects on substrate metabolism evidenced by greater fat oxidation without changes in RE. Acute low carbohydrate availability did not affect high intensity running performance across a range of distances.Highlights Acute manipulation of muscle glycogen availability using an exercise and dietary manipulation protocol did not affect subsequent high intensity running performance across a range of running distances.Reduced muscle glycogen resulted in a marked increase in fat oxidation in low glycogen condition but no changes in running economy or critical speed.Individual factors should be considered when prescribing high intensity sessions with restricted carbohydrate availability.

Carbohydrate mouth rinse is no more effective than placebo on running endurance of dehydrated and heat acclimated athletes

PURPOSE

To determine whether carbohydrate mouth rinsing would improve endurance running performance of tropical natives in a warm-humid (30 °C and 70% relative humidity) environment.

METHOD

Twelve endurance male runners [age 25 ± 3 years; peak aerobic capacity ([Formula: see text]O_2peak) 57.6 ± 3.6 mL^.kg^-1.min^-1] completed three time-to-exhaustion (TTE) trials at ~ 70% [Formula: see text]O_2peak while swilling 25 ml of a 6% carbohydrate (CHO) or taste-matched placebo (PLA) as well as no mouth rinse performed in the control (CON) trial.

RESULTS

TTE performance was significantly longer in both CHO and PLA trials when compared with the CON trial (54.7 ± 5.4 and 53.6 ± 5.1 vs. 48.4 ± 3.6 min, respectively; p < 0.001 and p = 0.012, respectively), but was not significantly different between CHO and PLA trials (p = 1.000). The rating of perceived exertion was not different between the CHO and PLA trials, however, was significantly affected when compared to the CON trial (p < 0.001). A similar effect was observed for perceived arousal level between the CHO and PLA trials to the CON trial. Core temperature, mean skin temperature and skin blood flow were not significantly different between the three trials (all p > 0.05). Similarly, plasma lactate and glucose as well as exercise heart rate were not influenced by the trials.

CONCLUSIONS

The present study demonstrates that mouth rinsing, whether carbohydrate or placebo, provides an ergogenic benefit to running endurance when compared to CON in a heat stress environment. Nevertheless, the results do not support the notion that rinsing a carbohydrate solution provides a greater advantage as previously described among non-heat acclimated individuals within a temperate condition.

Mouth rinsing and ingesting salty or bitter solutions does not influence corticomotor excitability or neuromuscular function

PURPOSE

To explore the effect of tasting unpleasant salty or bitter solutions on lower limb corticomotor excitability and neuromuscular function.

METHODS

Nine females and eleven males participated (age: 27 ± 7 years, BMI: 25.3 ± 4.0 kg m^-2). Unpleasant salty (1 M) and bitter (2 mM quinine) solutions were compared to water, sweetened water, and no solution, which functioned as control conditions. In a non-blinded randomized cross-over order, each solution was mouth rinsed (10 s) and ingested before perceptual responses, instantaneous heart rate (a marker of autonomic nervous system activation), quadricep corticomotor excitability (motor-evoked potential amplitude) and neuromuscular function during a maximal voluntary contraction (maximum voluntary force, resting twitch force, voluntary activation, 0-50 ms impulse, 0-100 impulse, 100-200 ms impulse) were measured.

RESULTS

Hedonic value (water: 47 ± 8%, sweet: 23 ± 17%, salt: 71 ± 8%, bitter: 80 ± 10%), taste intensity, unpleasantness and increases in heart rate (no solution: 14 ± 5 bpm, water: 18 ± 5 bpm, sweet: 20 ± 5 bpm, salt: 24 ± 7 bpm, bitter: 23 ± 6 bpm) were significantly higher in the salty and bitter conditions compared to control conditions. Nausea was low in all conditions (< 15%) but was significantly higher in salty and bitter conditions compared to water (water: 3 ± 5%, sweet: 6 ± 13%, salt: 7 ± 9%, bitter: 14 ± 16%). There was no significant difference between conditions in neuromuscular function or corticomotor excitability variables.

CONCLUSION

At rest, unpleasant tastes appear to have no influence on quadricep corticomotor excitability or neuromuscular function. These data question the mechanisms via which unpleasant tastes are proposed to influence exercise performance.

Carbohydrate Rinse Fails to Enhance Cycling Performance or Alter Metabolic and Autonomic Recovery in Recreational Cyclists

The purpose of the study was to examine the effects of carbohydrate (CHO) mouth rinsing on autonomic and metabolic recovery as well as cycling performance. Ten male recreational cyclists (age = 30 ± 6 years, VO_2peak = 54.5 ± 8.1 mL·kg^-1·min^-1) completed a randomized, double-blind, placebo-controlled, crossover designed study. A CHO or a placebo (PLA) rinse was administered every 12.5% of a work to completion trial (75%W_max). Heart rate variability (lnRMSSD), the respiratory exchange ratio, and plasma epinephrine, norepinephrine, insulin, glucose, free fatty acids (FFA), and lactate were measured pre- and post-exercise. The CHO rinse did not improve time to completion of the test trial (CHO: 4108 ± 307 s, PLA: 4176 ± 374 s, p = 0.545). Further, the CHO rinse did not impact autonomic recovery, as measured by lnRMSSD (p = 0.787) and epinephrine (p = 0.132). Metabolic biomarkers were also unaffected by the CHO rinse, with no differences observed in responses of FFA (p = 0.064), lactate (p = 0.302), glucose (p = 0.113) or insulin (p = 0.408). Therefore, the CHO mouth rinse does not reduce the acute sympathetic response following strenuous exercise and does not result in improvements in cycling time to completion.

A Narrative Review of Current Concerns and Future Perspectives of the Carbohydrate Mouth Rinse Effects on Exercise Performance

Previous systematic reviews have confirmed that carbohydrate (CHO) mouth rinse may boost physical exercise performance, despite some methodological aspects likely affecting its ergogenic effect. In this review, we discussed if the exercise mode, pre-exercise fasting status, CHO solutions concentration, CHO solutions temperature, mouth rinse duration, and CHO placebo effects may potentially reduce the CHO mouth rinse ergogenic effect, suggesting possible solutions to manage these potential confounders. The effectiveness of CHO mouth rinse as a performance booster is apparently related to the origin of the exercise-induced neuromuscular fatigue, as CHO mouth rinse unequivocally potentiates endurance rather than sprint and strength exercises performance. Furthermore, ergogenic effects have been greater in fasting than fed state, somehow explaining the varied magnitude of the CHO mouth rinse effects in exercise performance. In this regard, the CHO solution concentration and temperature, as well as the mouth rinse duration, may have increased the variability observed in CHO mouth rinse effects in fasting and fed state. Finally, placebo effects have challenged the potential of the CHO mouth rinse as an ergogenic aid. Therefore, we suggest that future studies should consider methodological controls such as sample size and sample homogeneity, proper familiarization with experimental procedures, and the use of alternative placebo designs to provide unbiased evidence regarding the potential of the CHO mouth rinse as an ergogenic aid.

Effect of carbohydrate mouth rinse on muscle strength and muscular endurance: A systematic review with meta-analysis

The present systematic review with meta-analysis summarized studies that investigated the effect of carbohydrate (CHO) mouth rinse on muscle strength and muscular endurance. The search was performed in six databases. Thirteen randomized clinical trials were selected and the standardized mean difference between CHO mouth rinse and placebo for maximal strength and muscular endurance was determined via a random-effects model using Review Manager 5.4 software. Meta-regression was also performed to explore the influence of load, number of sets, number of exercises, fasting time, CHO concentration, and number of mouth rinses on the main outcomes. There was no significant effect of CHO mouth rinse on maximal strength (mean difference= 0.25 kg, 95%CI - 1.81 to 2.32 kg, z = 0.24, p = 0.810). However, there was a significant positive effect of CHO mouth rinse on muscular endurance (mean difference = 1.24 repetitions, 95%CI 0.70 to 1.77 repetitions, z = 4.55, p < 0.001). Meta-regression identified that CHO mouth rinse has greater benefits on muscular endurance when using high workloads, multiple exercises, and a smaller number of mouth rinses (p = 0.001). In conclusion, CHO mouth rinse has no effect on maximal muscle strength but has a positive effect on muscular endurance and seems to optimize when fewer mouth rinses, high workloads and numbers of exercises are used.Supplemental data for this article is available online at https://doi.org/10.1080/10408398.2022.2057417.

Carbohydrate Mouth Rinse and Spray Improve Prolonged Exercise Performance in Recreationally Trained Male College Students

Mouth rinsing with a carbohydrate (CHO) solution has emerged as a sports nutrition strategy to increase endurance performance. This study aimed to clarify the effects of two forms of CHO sensing in the mouth (i.e., CHO mouth rinse (CMR) and CHO mouth spray (CMS)) on exercise performance during prolonged exercise, including ultra-high intensity intermittent exercise over time. We conducted the following experimental trials: (1) 6% glucose solution (G), (2) 6% CMR, (3) 6% CMS, and (4) water (WAT). These trials were conducted at least 1 week apart in a randomized crossover design. Eight male college students performed constant-load exercise for 60 min (intensity 40% VO2peak), four sets of the Wingate test (three 30 s Wingate tests with a 4 min recovery between each test), and a constant-load exercise for 30 min (intensity 40% VO2peak). The mean exercise power output (Watt), ratings of perceived exertion, and blood glucose levels were measured. We found that the mean power values of the CMR and CMS in the third and fourth sets was significantly higher than that of WAT (p < 0.05), and that the G trial did not show a significant difference from any other trial. Thus, when compared to G or WAT, CMR and CMS can help improve endurance exercise performance.

Maltodextrin-Based Carbohydrate Oral Rinsing and Exercise Performance: Systematic Review and Meta-Analysis

Background

Carbohydrates are an important fuel for optimal exercise performance during moderate- and high-intensity exercise; however, carbohydrate ingestion during high-intensity exercise may cause gastrointestinal upset. A carbohydrate oral rinse is an alternative method to improve exercise performance in moderate- to high-intensity exercise with a duration of 30–75 min. This is the first systematic review and meta-analysis to comprehensively examine the isolated effect of maltodextrin-based rinsing on exercise performance.

Objective

The objective of this review was to establish the effect of a maltodextrin-based carbohydrate oral rinse on exercise performance across various modes of exercise. Furthermore, a secondary objective was to determine the effects of moderators [(1) participant characteristics; (2) oral rinse protocols; (3) exercise protocol (i.e. cycling, running etc.) and (4) fasting] on exercise performance while using a maltodextrin-based, carbohydrate oral rinse.

Methods

Five databases (MEDLINE, PsycINFO, Embase, SPORTDiscus and Global Health) were systematically searched for articles up to March 2021 and screened using Covidence (a systematic review management tool). A random effects robust meta-analysis and subgroup analyses were performed using Stata Statistical Software: Release 16.

Results

Thirty-five articles met the inclusion criteria and were included in the systematic review; 34 of these articles were included in the meta-analysis. When using a conventional meta-analytic approach, overall, a carbohydrate oral rinse improved exercise performance in comparison with a placebo (SMD = 0.15, 95% CI 0.04, 0.27; p = 0.01). Furthermore, when implementing an adjusted, conservative, random effects meta-regression model using robust variance estimation, overall, compared with placebo, a carbohydrate oral rinse demonstrated evidence of improving exercise performance with a small effect size (SMD = 0.17, 95% CI − 0.01, 0.34; p = 0.051).

Conclusion

This systematic review and meta-analysis demonstrates that a maltodextrin-based carbohydrate oral rinse can improve exercise performance. When comparing the two meta-analytic approaches, although non-significant, the more robust, adjusted, random effects meta-regression model demonstrated some evidence of a maltodextrin-based carbohydrate oral rinse improving exercise performance overall.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-022-01658-3.

Carbohydrate Mouth Rinse Increases High but Not Low Intensity Repetitions to Failure in Resistance-Trained Males

Carbohydrate mouth rinsing (CMR) has been shown to enhance exercise performance. However, the influence of CMR on repetitions to failure with different intensities (40% or 80% of 1 RM) is unknown. Therefore, the purpose of this study was to examine the effects of a 6% CMR solution on muscular endurance assessed at 40% and 80% of 1 RM in resistance-trained males. Sixteen resistance-trained males (age: 25 ± 3 years, height: 182 ± 6 cm, body mass: 86 ± 3 kg, body fat: 16 ± 3%, bench press 1 RM: 106 ± 16 kg, resistance training experience: 5 ± 1 years) completed four conditions in random order. The four conditions consisted of ten seconds of mouth rinsing with 25 mL solutions containing either maltodextrin or placebo (sweetened water) prior to performing a bench press muscular endurance test at either 40% of 1 RM or 80% of 1 RM. Total repetitions, heart rate (HR), ratings of perceived exertion (RPE), glucose (GLU) and felt arousal (FA) were recorded for each condition. There was a significant condition by intensity interaction (p = 0.02). CMR significantly increased total repetitions compared with placebo at the higher intensity (80% of 1 RM; p = 0.04), while there was no effect at the lower intensity (p = 0.20). In addition, HR, RPE, GLU and FA did not differ between conditions or across intensities (p > 0.05). In conclusion, CMR-enhanced muscular endurance performed at higher but not lower intensities.

No independent or synergistic effects of carbohydrate-caffeine mouth rinse on repeated sprint performance during simulated soccer match play in male recreational soccer players

The study examined the synergistic and independent effects of carbohydrate-caffeine mouth rinse on repeated sprint performance during simulated soccer match play. Nine male soccer players (21 ± 3 years, 1.75 ± 0.05 m, 68.0 ± 9.0 kg) completed four trials with either 6 mg·kg^-1 caffeine + 10% maltodextrin (CHO+CAFMR), 6 mg·kg^-1 caffeine (CAFMR), 10% maltodextrin (CHOMR), water (PLA) in a block randomised, double-blinded, counterbalanced and crossover manner separated by minimum 96 h. All solutions were taste-matched and a carbohydrate-rich meal (2 g·kg^-1body mass) was provided 2 h before each trial. Each trial consisted of a 90-min soccer-specific aerobic field test (SAFT⁹⁰) and two bouts of repeated sprint ability tests (RSAT; 6 × 6 s sprints with 24 s recovery) completed at 0 min and 75^th min of SAFT⁹⁰. A 25 ml solution of either CHO+CAFMR, CAFMR, CHOMR or PLA was rinsed immediately before the second RSAT (75 min). Mean power output, peak power output (PPO) or fatigue index (FI) was not impacted by any treatment during the 75^th min RAST (p > 0.05). These results suggest that carbohydrate and/or caffeine mouth rinses do not have an ergogenic effect during simulated soccer exercise after a high carbohydrate meal.

Carbohydrate Mouth Rinsing Does Not Alter Central or Peripheral Fatigue After High-Intensity and Low-Intensity Exercise in Men

ABSTRACT

Black, CD, Haskins, KR, Bemben, MG, and Larson, RD. Carbohydrate mouth rinsing does not alter central or peripheral fatigue after high-intensity and low-intensity exercise in men. J Strength Cond Res 36(1): 142-148, 2022-Carbohydrate (CHO) mouth rinsing improves performance during endurance exercise. However, its ability to attenuate fatigue during strength-based exercise is less certain. This study sought to determine the effects of a CHO mouth rinse on torque production and voluntary activation (VA%) after high-intensity and low-intensity isometric exercise. Twelve male subjects (22.5 ± 2.3 years; 183.5 ± 6.5 cm; 82.2 ± 13.9 kg) completed 4 testing sessions in a double-blind crossover fashion. Knee extension maximal voluntary isometric strength (MVC) was assessed before(Pre), immediately (iPost-Ex), and 5 minutes (5-min Post Ex) after isometric exercise performed at 80% or 20% of MVC. An 8% CHO solution or placebo (PLA) was rinsed for 20 seconds after exercise. VA% was determined by twitch interpolation. A 2 condition (CHO vs. PLA) × 2 contraction intensity (20 vs. 80%) × 3 time (Pre, iPost Ex, and 5-min Post Ex) completely within subject-repeated measured analysis of variance was performed; statistical significance was set at p ≤ 0.05. Greater reductions in MVC were found at iPost-Ex after exercise at 20% compared with 80% of MVC (-25 ± 14% vs. -11 ± 8%; p < 0.001) as well as for VA% (-17 ± 14% vs. -8 ± 14%; p < 0.004). No differences were observed in the CHO vs. PLA condition (p ≥ 0.34). We were successful in eliciting differing levels of central and peripheral fatigue by exercising at a low and high intensity. Despite significantly larger declines in VA% after exercise at 20% of MVC, CHO mouth rinsing had no effects compared with placebo on any measured variable.

The Effect of Isolated and Combined Application of Menthol and Carbohydrate Mouth Rinses on 40 km Time Trial Performance, Physiological and Perceptual Measures in the Heat

The current study compared mouth swills containing carbohydrate (CHO), menthol (MEN) or a combination (BOTH) on 40 km cycling time trial (TT) performance in the heat (32 °C, 40% humidity, 1000 W radiant load) and investigates associated physiological (rectal temperature (Trec), heart rate (HR)) and subjective measures (thermal comfort (TC), thermal sensation (TS), thirst, oral cooling (OC) and RPE (legs and lungs)). Eight recreationally trained male cyclists (32 ± 9 y; height: 180.9 ± 7.0 cm; weight: 76.3 ± 10.4 kg) completed familiarisation and three experimental trials, swilling either MEN, CHO or BOTH at 10 km intervals (5, 15, 25, 35 km). The 40 km TT performance did not differ significantly between conditions (F2,14 = 0.343; p = 0.715; η2 = 0.047), yet post-hoc testing indicated small differences between MEN and CHO (d = 0.225) and MEN and BOTH (d = 0.275). Subjective measures (TC, TS, RPE) were significantly affected by distance but showed no significant differences between solutions. Within-subject analysis found significant interactions between solution and location upon OC intensity (F28,196 = 2.577; p < 0.001; η2 = 0.269). While solutions containing MEN resulted in a greater sensation of OC, solutions containing CHO experienced small improvements in TT performance. Stimulation of central CHO pathways during self-paced cycling TT in the heat may be of more importance to performance than perceptual cooling interventions. However, no detrimental effects are seen when interventions are combined.

Nutritional approaches to counter performance constraints in high-level sports competition

New Findings

What is the topic of this review?

The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them.

What advances does it highlight?

A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event‐specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real‐life sport for optimal implementation.

Abstract

High‐performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low‐carbohydrate high‐fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst‐driven drinking) to fluid intake.

Commercially available carbohydrate drink with menthol fails to improve thermal perception or cycling exercise capacity in males

The purpose of this double-blinded, crossover randomized and counterbalanced study was to compare the effects of ingesting a tepid commercially available carbohydrate-menthol-containing sports drink (menthol) and an isocaloric carbohydrate-containing sports drink (placebo) on thermal perception and cycling endurance capacity "in a simulated home virtual cycling environment". It was hypothesized that the addition of menthol would improve indicators of thermal perception and improve endurance exercise capacity. Twelve healthy, endurance-trained males (age 29 ± 5 years, height 181 ± 6 cm, body mass 79 ± 2 kg and V̇O₂max 57.3 ± 6.4 mL kg^-1 min^-1) completed two experimental trials on a stationary bicycle without external air flow. Each trial consisted of (1) cycling for 60 min at 90% of the first ventilatory threshold while receiving a fixed amount of menthol or placebo every 10 min followed immediately by (2) cycling until volitional exhaustion (TTE) at 105% of the intensity corresponding to the respiratory compensation point. TTE did not differ between both conditions (541 ± 177 and 566 ± 150 s for menthol and placebo; p > 0.05) and neither did ratings of perceived thermal comfort or thermal sensation (p > 0.05). Also, the rectal temperature at the end of TTE was comparable between menthol and placebo trials (38.7 ± 0.2°C and 38.7 ± 0.3°C, respectively; p > 0.05). The present results demonstrate that the addition of menthol to commercially available sports drink does not improve thermal comfort or endurance exercise capacity during ∼65 min of intense virtual cycling.

Is caffeine mouth rinsing an effective strategy to improve physical and cognitive performance? A systematic review

The aim of this study was to perform a systematic review on the effects of caffeine mouth rinsing on physical and cognitive performance. Following a search through 4 databases, 18 studies were found meeting the inclusion criteria (15 for physical performance and 3 for cognitive performance). All selected studies found an improvement in cognitive performance with caffeine mouth rinse. Four studies found positive effects of caffeine mouthwash on physical performance when repeated during exercise, while one study detected a positive effect with a single mouthwash before exercise, but only in a fasted state. Among these studies that showed positive effects, however, three (2 for physical performance and 1 for cognitive performance) presented fair methodological quality. There was also a variety of methodological approaches in the studies that showed no improvement in physical performance with caffeine mouth rinse, which may have influenced the potential to detect the ergogenic effect of caffeine mouth rinse. Thus, the effects of caffeine mouth rinse on physical performance are mixed, but a potential ergogenic effect might be present in a fasted state and when mouthwash is repeated during exercise. Concerning cognitive performance, caffeine mouth rinse seems to be a beneficial strategy.

Perceptual and Physiological Responses to Carbohydrate and Menthol Mouth-Swilling Solutions: A Repeated Measures Cross-Over Preliminary Trial

Carbohydrate and menthol mouth-swilling have been used to enhance exercise performance in the heat. However, these strategies differ in mechanism and subjective experience. Participants (n = 12) sat for 60 min in hot conditions (35 °C; 15 ± 2%) following a 15 min control period, during which the participants undertook three 15 min testing blocks. A randomised swill (carbohydrate; menthol; water) was administered per testing block (one swill every three minutes within each block). Heart rate, tympanic temperature, thermal comfort, thermal sensation and thirst were recorded every three minutes. Data were analysed by ANOVA, with carbohydrate intake controlled for via ANCOVA. Small elevations in heart rate were observed after carbohydrate (ES: 0.22 ± 90% CI: −0.09–0.52) and water swilling (0.26; −0.04–0.54). Menthol showed small improvements in thermal comfort relative to carbohydrate (−0.33; −0.63–0.03) and water (−0.40; from −0.70 to −0.10), and induced moderate reductions in thermal sensation (−0.71; from −1.01 to −0.40 and −0.66; from −0.97 to −0.35, respectively). Menthol reduced thirst by a small to moderate extent. These effects persisted when controlling for dietary carbohydrate intake. Carbohydrate and water may elevate heart rate, whereas menthol elicits small improvements in thermal comfort, moderately improves thermal sensation and may mitigate thirst; these effects persist when dietary carbohydrate intake is controlled for.

The Effects of Caffeine Mouth Rinsing on Exercise Performance: A Systematic Review

Caffeine ingestion can improve performance across a variety of exercise modalities but can also elicit negative side effects in some individuals. Thus, there is a growing interest in the use of caffeine mouth rinse solutions to improve sport and exercise performance while minimizing caffeine’s potentially adverse effects. Mouth rinse protocols involve swilling a solution within the oral cavity for a short time (e.g., 5–10 s) before expectorating it to avoid systemic absorption. This is believed to improve performance via activation of taste receptors and stimulation of the central nervous system. Although reviews of the literature indicate that carbohydrate mouth rinsing can improve exercise performance in some situations, there has been no attempt to systematically review the available literature on caffeine mouth rinsing and its effects on exercise performance. To fill this gap, a systematic literature search of three databases (PubMed, SPORTDiscus, and Web of Science) was conducted by two independent reviewers. The search resulted in 11 randomized crossover studies that were appraised and reviewed. Three studies found significant positive effects of caffeine mouth rinsing on exercise performance, whereas the remaining eight found no improvements or only suggestive benefits. The mixed results may be due to heterogeneity in the methods across studies, interindividual differences in bitter tasting, and differences in the concentrations of caffeine solutions. Future studies should evaluate how manipulating the concentration of caffeine solutions, habitual caffeine intake, and genetic modifiers of bitter taste influence the efficacy of caffeine mouth rinsing as an ergogenic strategy.

Carbohydrate mouth rinse improves resistance exercise capacity in the glycogen-lowered state

The effect of carbohydrate mouth rinse (CHO MR) on resistance exercise performance is equivocal and may be moderated by carbohydrate availability. This study determined the effect of CHO MR on low-load resistance exercise capacity completed in a fed but glycogen-lowered state. Twelve resistance-trained men (age: 22 ± 4 years; height: 1.79 ± 0.05 m; mass: 78.7 ± 7.8 kg; bench press one-repetition maximum (1RM): 87 ± 21 kg; squat 1RM: 123 ± 19 kg) completed two fed-state resistance exercise bouts consisting of six sets of bench press and six sets of squat to failure at 40% 1RM. Each bout was preceded by glycogen-depleting cycling the evening before, with feeding controlled to create acute energy deficit and maintain low muscle glycogen. During resistance exercise, participants rinsed with either a 6% CHO MR solution or a taste-matched placebo (PLA) between sets. Total volume workload was greater with CHO MR (9354 ± 2051 vs. 8525 ± 1911 kg, p = 0.010). Total number of repetitions of squat were greater with CHO MR (107 ± 26 vs. 92 ± 16, p = 0.017); the number of repetitions of bench press were not significantly different (CHO MR: 120 ± 24 vs. PLA: 115 ± 22, p = 0.146). This was independent of differences in feeling or arousal. CHO MR may be an effective ergogenic aid for athletes completing resistance exercise when in energy deficit and with low carbohydrate availability. Novelty: CHO MR can increase low-load resistance exercise capacity undertaken in a glycogen-lowered but fed state. This effect was driven by a greater number of repetitions-to-failure in the squat - using muscles lowered in glycogen content with exhaustive cycling on the evening prior to resistance exercise - but not bench press.

The Performance Effect of Scheduled Carbohydrate and Caffeine Intake during Simulated Team Sport Match-Play

The aim of the current investigation was to identify the effects of scheduled carbohydrate (CHO) and caffeine (CAF) supplementation on simulated team sport match-play performance. Ten male hurling players completed three hurling match-play simulation protocols (HSP) performed 7 days apart in a double-blind, randomized design. Supplementation included CHO, CHO + CAF, and placebo (PLA). In a randomized order, participants ingested either a 6% CHO solution, a PLA solution of similar taste, or a combined intake of 6% CHO solution + 200 mg CAF capsule. At specific time points (Pre-0 min; half time (HT)-30 min; full time (FT)-60 min), participants completed a repeated sprint protocol (RAST; 12 × 20 m). Physiological [% maximal oxygen uptake (%VO_2max), % mean oxygen uptake (%VO_2mean), % maximal heart rate (%HR_max), % mean heart rate (%HR_mean), respiratory exchange ratio (RER), and blood lactate (BLa)] and performance [(best sprint time (RSA_best), mean sprint time (RSA_mean), and rate of perceived exertion (RPE)] variables were monitored throughout each simulation. Non-significant differences were observed between supplement trials (CHO, CHO + CAF, and PLA) for BLa (η² = 0.001, small), %VO_2max (η² = 0.001, small), %VO_2mean (η² = 0.004, small), %HR_max (η² = 0.007, small), %HR_mean (η² = 0.018, small), RER (η² = 0.007, small), RPE (η² = 0.007, small), and RSA_best (η² = 0.050, small). RSA_mean performance significantly improved in CHO + CAF trials compared to PLA, with sprint times significantly improved from Pre to FT also (η² = 0.135, medium). A significant difference was observed in BLa between time points (Pre, HT, and FT) (η² = 0.884, large) in % HRmax (η² = 0.202, medium), %HR_mean (η² = 0.477, large), and RER (η² = 0.554, large) across halves and in RPE across time points (η² = 0.670, large). Our data provide novel data regarding the effects of CHO and CAF supplementation on team sport performance, with co-ingestion of CHO + CAF reducing the decrement in repeated sprint performance compared to PLA.

Effects of Carbohydrate Mouth Rinse on Cycling Time Trial Performance: A Systematic Review and Meta-Analysis

BACKGROUND

Despite the growing number of studies reporting carbohydrate mouth rinse effects on endurance performance, no systematic and meta-analysis review has been conducted to elucidate the level of evidence of carbohydrate mouth rinse effects on cycling trial performance such as time-, work-, and distance-based trials.

OBJECTIVES

The objective of this study were to establish the effect of a carbohydrate mouth rinse on cycling performance outcomes such as mean power output and time to complete a trial, together with the risk of bias in the cycling-carbohydrate mouth rinse literature.

METHODS

We systematically reviewed randomized placebo-controlled trials that assessed carbohydrate mouth rinse effects on mean power output and time to complete the trial. A random-effects meta-analysis assessed the standardized mean difference between carbohydrate and placebo mouth rinses.

RESULTS

Thirteen studies (16 trials) were qualitatively (systematic review) and quantitatively (meta-analysis) analyzed with regard to mean power output (n = 175) and time to complete the trial (n = 151). Overall, the reviewed studies showed a low risk of bias and homogeneous results for mean power output (I² = 0%) and time to complete the trial (I² = 0%). When compared with placebo, the carbohydrate mouth rinse improved mean power output (standardized mean difference = 0.25; 95% confidence interval 0.04-0.46; p = 0.02), but not the time to complete the trial (standardized mean difference = - 0.13; 95% confidence interval - 0.36 to 0.10; p = 0.25).

CONCLUSION

The present systematic and meta-analytic review supports the notion that a carbohydrate mouth rinse has the potential to increase mean power output in cycling trials, despite showing no superiority over placebo in improving time to complete the trials.

Effect of glucose and sodium chloride mouth rinses on neuromuscular fatigue: a preliminary study

Carbohydrate (CHO) mouth rinse has been shown to improve endurance performance and maintain the central drive of contracting muscles. Salt (NaCl) mouth rinse solution, often used in dentistry to desensitise the oral cavity to pain, could also activate cortical areas of the brain. Hence, the objective of this preliminary study was to investigate whether CHO (glucose) and NaCl mouth rinses could attenuate the reduction in maximum voluntary contraction (MVC) and sustained MVC (sMVC) following an endurance exercise (30-minute cycling at 70% VO₂max). Ten subjects (male, age: 22 ± 1 years, weight: 65.3 ± 12.4 kg, height: 164.5 ± 7.5 cm, VO₂max: 48.3 ± 6.1 mL kg^-1 min^-1) completed three trials of 30-minute cycling exercise. In a randomised cross-over study, in each trial, the participants rinsed using either water, 6% glucose, or 6% NaCl solution for 5 s immediately prior to and every 10 min during the cycling exercise. The MVC and sMVC were measured pre and post cycling. Analysis of variance showed significant interaction and time effects for MVC, while for sMVC there was a significant interaction with time and group effects. Both MVC and sMVC were higher post cycling in the glucose and NaCl groups compared to the water group, which suggests that activation of glucose and NaCl oral receptors could better preserve post-exercise force production. This is the first study to show that NaCl mouth rinse can produce a comparable effect on glucose. Hence, mouth rinses may be able to activate other distinct pathways that could attenuate fatigue.

Effect of Carbohydrate Mouth Rinse on Training Load Volume in Resistance Exercises

Bastos-Silva, VJ, Prestes, J, and Geraldes, AAR. Effect of carbohydrate mouth rinse on training load volume in resistance exercises. J Strength Cond Res 33(6): 1654-1658, 2019-The aim of this study was to investigate the effect of carbohydrate (CHO) mouth rinse on training load volume (TLV-number of repetitions × load lifted [kg]) on 2 resistance exercises: leg press (LP) and bench press (BP). Twelve recreational resistance trained males were recruited. Subjects were assessed for 1 repetition maximum (1RM) and muscular endurance (ME) in LP and BP. Muscular endurance was determined by the maximum number of repetitions performed to volitional fatigue, with a load equal to 80% of 1RM. Exercises were performed on separate days (72 hours apart) under 3 experimental conditions: control (CONT), CHO (25 ml with 6.4% of maltodextrin), and placebo (juice without CHO [PLA]). Carbohydrate and PLA were used immediately before each exercise. There was no significant difference between conditions for the number of repetitions (CHO = 13.5 ± 4.8; PLA = 11.5 ± 4.4; CONT = 12.4 ± 4.4, p = 0.68) nor TLV (CHO = 2006.7 ± 825.2 kg; PLA = 1712.5 ± 772.9 kg; CONT = 1817.1 ± 672.6 kg, p = 0.99) in LP. However, CHO increased both repetitions (CHO = 8.2 ± 1.6; PLA = 7.1 ± 2.4; CONT = 6.8 ± 1.8, p = 0.002) and TLV (CHO = 557.1 ± 155.4 kg; PLA = 495.9 ± 206.1 kg; CONT = 476.1 ± 175.3 kg, p = 0.035) compared with CON in BP. Thus, a CHO mouth rinse increases BP performance in trained men, suggesting an interesting strategy to be used by experienced resistance training practitioners.

Mouth Rinsing Cabohydrates Serially Does Not Improve Repeated Sprint Time

Sensing carbohydrates via the oral cavity benefits performance outcomes during brief high intensity bouts of exercise. However, the extent to which carbohydrates need to be present in the oral cavity to influence sprint performance is less understood. The purpose of this study was to determine if serial increases in carbohydrate rinse time across sprint sets attenuates increases in sprint time compared to no serial increases in carbohydrate rinse time across sprint sets. Fifteen sprint trained participants completed three repeated anaerobic sprint tests (RAST), 3 sets of 6 x 35-m sprints, under two different carbohydrate mouth rinsing (CMR) conditions; (1) rinsing for only 5 seconds (s), and (2) rinsing for 5 s, 10 s and 15 s (serial rinse). Prior to a RAST, participants provided perceived recovery status (PRS) and perceived feeling of arousal (FAS). Upon completion of each individual sprint, participants gave a rating of perceived exertion (RPE). A lactate sample was taken upon completion of each individual sprint set and after all 3 RASTs a session rating of perceived exertion (S-RPE) was measured. There were no significant differences in peak (p = 0.18) and average sprint time (p = 0.41). There were no significant differences in perceptual measures: RPE, PRS, FAS, S-RPE or for blood lactate concentration between CMR conditions. Overall, serial rinsing resulted in changes that were most likely trivial, but showed a 50% chance in perceiving a sprint session as less difficult. Rinsing carbohydrates in a serial manner between repeated sprint sets produces trivial changes of sprint speed and perceptual measures from sprint performance.

Carbohydrate Availability and Physical Performance: Physiological Overview and Practical Recommendations

Strong evidence during the last few decades has highlighted the importance of nutrition for sport performance, the role of carbohydrates (CHO) being of special interest. Glycogen is currently not only considered an energy substrate but also a regulator of the signaling pathways that regulate exercise-induced adaptations. Thus, low or high CHO availabilities can result in both beneficial or negative results depending on the purpose. On the one hand, the depletion of glycogen levels is a limiting factor of performance during sessions in which high exercise intensities are required; therefore ensuring a high CHO availability before and during exercise is of major importance. A high CHO availability has also been positively related to the exercise-induced adaptations to resistance training. By contrast, a low CHO availability seems to promote endurance-exercise-induced adaptations such as mitochondrial biogenesis and enhanced lipolysis. In the present narrative review, we aim to provide a holistic overview of how CHO availability impacts physical performance as well as to provide practical recommendations on how training and nutrition might be combined to maximize performance. Attending to the existing evidence, no universal recommendations regarding CHO intake can be given to athletes as nutrition should be periodized according to training loads and objectives.

The ergogenic potency of carbohydrate mouth rinse on endurance running performance of dehydrated athletes

PURPOSE

To examine the effect of carbohydrate (CHO) mouth rinsing on endurance running responses and performance in dehydrated individuals.

METHODS

In a double blind, randomised crossover design, 12 well-trained male runners completed 4 running time to exhaustion (TTE) trials at a speed equivalent to 70% of VO_2peak in a thermoneutral condition. Throughout each run, participants mouth rinsed and expectorated every 15 min either 25 mL of 6% CHO or a placebo (PLA) solution for 10 s. The four TTEs consisted of two trials in the euhydrated (EU-CHO and EU-PLA) and two trials in the dehydrated (DY-CHO and DY-PLA) state. Prior to each TTE run, participants were dehydrated via exercise and allowed a passive rest period during which they were fed and either rehydrated equivalent to their body mass deficit (i.e., EU trials) or ingested only 50 mL of water (DY trials).

RESULTS

CHO mouth rinsing significantly improved TTE performance in the DY compared to the EU trials (78.2 ± 4.3 vs. 76.9 ± 3.8 min, P = 0.02). The arousal level of the runners was significantly higher in the DY compared to the EU trials (P = 0.02). There was no significant difference among trials in heart rate, plasma glucose and lactate, and psychological measures.

CONCLUSIONS

CHO mouth rinsing enhanced running performance significantly more when participants were dehydrated vs. euhydrated due to the greater sensitivity of oral receptors related to thirst and central mediated activation. These results show that level of dehydration alters the effect of brain perception with presence of CHO.

Carbohydrate Mouth Rinse Decreases Time to Complete a Simulated Cycling Time Trial

Rinsing carbohydrate solutions in the mouth can produce positive effects on the central nervous system via mouth/tongue receptors, ultimately increasing cycling performance. However, previous investigations on this topic have used complex carbohydrate solutions and time trials on a cyclergometer to complete a set amount of work. The purpose of the present study was to examine the effects of carbohydrate mouth rinsing on physical performance by using a commercially available drink during a cycling time trial with varying slopes. In a double-blind, placebo-controlled and randomized manner, 16 well-trained cyclists (37.6 ± 3.5 years; 76.9 ± 7.9 kg) performed two simulated cycling time trial (25.3 km) with their own bikes on a 3D virtual trainer. In one occasion, participants mouth-rinsed a 6.4% carbohydrate mixed solution for 5 s each 12.5% of total completion of the trial; in other occasion participants rinsed with a taste-matched placebo with 0.0% of carbohydrate. During the trials, participants were instructed to perform as fast as possible at a self-chosen pace while time, cycling power output and ratings of perceived exertion were obtained during the trials. When compared to the placebo, carbohydrate mouth rinse decreased the time employed to complete the distance (2,960 ± 412 vs. 2,888 ± 396 s; P = 0.04, respectively), while it increased overall cycling power (222 ± 51 vs. 231 ± 46 w, P = 0.04) and cycling power during the climbing sections (238 ± 46 vs. 248 ± 47 w, P = 0.03). Carbohydrate mouth rinse also increased the rating of perceived exertion at the end of the trial (18.3 ± 1.7 vs. 18.9 ± 1.1 arbitrary units, P = 0.04). In summary, mouth rinsing with a commercially available carbohydrate drink might be considered as an effective strategy to increase physical performance during cycling time trials. However, due to the performance downsides of breaking the aero-position or interrupting the breathing pattern for rising during a time trial, carbohydrate mouth rinse protocols might be more suitable for high-intensity training sessions, particularly those sessions intentionally performed with low carbohydrate intake.

The Effect of Caffeine Ingestion and Carbohydrate Mouth Rinse on High-Intensity Running Performance

The aim of the current study was to investigate whether carbohydrate mouth rinsing works synergistically with caffeine to augment high-intensity running in a fed state. Eight participants completed a total of three trials; (1) placebo (PLA) trial (placebo capsule + placebo mouth rinse), (2) caffeine (CAF) trial (400 mg caffeine + placebo mouth rinse) and (3) carbohydrate mouth rinse + caffeine (CMR + CAF) trial (400 mg caffeine + 6% carbohydrate mouth rinse). Each trial consisted of a 45 min steady-state run at 65% VO_2max, followed by 90% VO_2max high-intensity intervals (HIIT) at 1 min and subsequently by a 1 min recovery walking at 6 km·h⁻¹, until exhaustion. Both CAF (46.8 ± 20.1 min) and CMR + CAF (46.9 ± 18.4 min) time to exhaustion were significantly greater than the PLA group (36.2 ± 14.8 min, p < 0.001). Post hoc analysis revealed that there was a significant increase in time to exhaustion between PLA and CMR + CAF (p = 0.006) and PLA and CAF (p = 0.017) but not between CAF and CMR + CAF (p = 0.99). In conclusion, we provide novel data that suggest that caffeine alone would likely suffice as an ergogenic aid during high-intensity running while in a fed state.

Effect of Carbohydrate Mouth Rinse on Performance after Prolonged Submaximal Cycling

Previous studies have shown improved shorter duration (∼1 h) performance with carbohydrate (CHO) mouth rinsing (WASH), especially in overnight fasted/non-fuelled subjects.

PURPOSE

To determine the effect of WASH on cycling time trial (TT) performance and muscle activity (EMG) after 2 h of submaximal cycling while receiving CHO (FED).

METHODS

In a double-blind, placebo-controlled crossover design, 10 well-trained males cyclists (V˙O2max: 65 mL·kg·min) completed two experimental trials. Each trial consisted of a standardized pretrial snack (2 h prior) followed by 120 min of steady-state (SS) cycling (∼60% V˙O2max) followed by an approximately 30-min TT, randomized as follows: 1) 30 g CHO·h during SS + WASH during TT (every 20% of TT) (FEDWASH); 2) 30 g CHO·h during SS + placebo (PLA) wash during TT (FEDPLA).

RESULTS

Although FEDWASH was not significantly different than FEDPLA (P = 0.51), there was a 1.7% (90% confidence interval, +6.4% to -3.2%; ES, 0.21) decrease in TT time (35 s) for FEDWASH compared with FEDPLA, with qualitative probabilities of a 60% positive and 23% trivial outcome. For EMG, soleus showed significant increase, whereas medial gastrocnemius showed significant decrease in muscle recruitment from the beginning 20% TT segment to the last 20% only in the FEDPLA condition, which coincided with a slower (P = 0.01) last 20% of the TT in FEDPLA versus FEDWASH.

CONCLUSIONS

Contrary to previous studies, this investigation utilized conditions of high ecological validity including a pretrial snack and CHO during SS. Significant changes in muscle recruitment and time over the last 20% of the TT, along with an average 1.7% improvement in TT time, suggest CHO mouth rinse helps maintain power output late in TT compared with placebo. Although marginal gains were achieved with a CHO mouth rinse (35 s), small performance effects can have significant outcomes in real-world competitions.

From Paper to Podium: Quantifying the Translational Potential of Performance Nutrition Research

Sport nutrition is one of the fastest growing and evolving disciplines of sport and exercise science, demonstrated by a 4-fold increase in the number of research papers between 2012 and 2018. Indeed, the scope of contemporary nutrition-related research could range from discovery of novel nutrient-sensitive cell-signalling pathways to the assessment of the effects of sports drinks on exercise performance. For the sport nutrition practitioner, the goal is to translate innovations in research to develop and administer practical interventions that contribute to the delivery of winning performances. Accordingly, step one in the translation of research to practice should always be a well-structured critique of the translational potential of the existing scientific evidence. To this end, we present an operational framework (the "Paper-2-Podium Matrix") that provides a checklist of criteria for which to prompt the critical evaluation of performance nutrition-related research papers. In considering the (1) research context, (2) participant characteristics, (3) research design, (4) dietary and exercise controls, (5) validity and reliability of exercise performance tests, (6) data analytics, (7) feasibility of application, (8) risk/reward and (9) timing of the intervention, we aimed to provide a time-efficient framework to aid practitioners in their scientific appraisal of research. Ultimately, it is the combination of boldness of reform (i.e. innovations in research) and quality of execution (i.e. ease of administration of practical solutions) that is most likely to deliver the transition from paper to podium.

Toward a Common Understanding of Diet-Exercise Strategies to Manipulate Fuel Availability for Training and Competition Preparation in Endurance Sport

From the breakthrough studies of dietary carbohydrate and exercise capacity in the 1960s through to the more recent studies of cellular signaling and the adaptive response to exercise in muscle, it has become apparent that manipulations of dietary fat and carbohydrate within training phases, or in the immediate preparation for competition, can profoundly alter the availability and utilization of these major fuels and, subsequently, the performance of endurance sport (events >30 min up to ∼24 hr). A variety of terms have emerged to describe new or nuanced versions of such exercise-diet strategies (e.g., train low, train high, low-carbohydrate high-fat diet, periodized carbohydrate diet). However, the nonuniform meanings of these terms have caused confusion and miscommunication, both in the popular press and among the scientific community. Sports scientists will continue to hold different views on optimal protocols of fuel support for training and competition in different endurance events. However, to promote collaboration and shared discussions, a commonly accepted and consistent terminology will help to strengthen hypotheses and experimental/experiential data around various strategies. We propose a series of definitions and explanations as a starting point for a more unified dialogue around acute and chronic manipulations of fat and carbohydrate in the athlete's diet, noting philosophies of approaches rather than a single/definitive macronutrient prescription. We also summarize some of the key questions that need to be tackled to help produce greater insight into this exciting area of sports nutrition research and practice.

Repeated-sprints exercise in daylight fasting: carbohydrate mouth rinsing does not affect sprint and reaction time performance

To determine the effect of carbohydrate mouth rinsing (CHO-MR) on physical and cognitive performance during repeated-sprints (RS) after 3 days of intermittent fasting (abstaining from food and fluid 14 h per day). In a randomized and counter-balanced manner 15 active healthy males in a fasted state performed a RS-protocol [RSP; 2 sets (SET1 and SET2) of 5×5 s maximal sprints, with each sprint interspersed with 25 s rest and 3 min of recovery between SET1 and SET2] on an instrumented non-motorized treadmill with embedded force sensors under three conditions: i) Control (CON; no-MR), ii) Placebo-MR (PLA-MR; 0% maltodextrin) and iii) CHO-MR (10% maltodextrin). Participants rinsed their mouth with either 10 mL of PLA-MR or CHO-MR solution for 5 s before each sprint. Sprint kinetics were measured for each sprint and reaction time (RTI) tasks (simple and complex) were assessed pre-, during- and post-RSP. There was no statistical main effect of CHO-MR on mean power, mean speed, and vertical stiffness during the sprints between the PLA-MR and CON condition. Additionally, no statistical main effect for CHO-MR on accuracy, movement time and reaction time during the RTI tasks was seen. CHO-MR did not affect physical (RSP) or cognitive (RTI) performance in participants who had observed 3 days of intermittent fasting (abstaining from food and fluid 14 h per day).

Dietary Manipulations Concurrent to Endurance Training

The role of an athlete's dietary intake (both timing and food type) goes beyond simply providing fuel to support the body's vital processes. Nutritional choices also have an impact on the metabolic adaptations to training. Over the past 20 years, research has suggested that strategically reducing carbohydrate (CHO) availability during an athlete's training can modify the metabolic responses in lieu of simply maintaining a high CHO diet. Several methods have been explored to manipulate CHO availability and include: Low-carb, high-fat (LCHF) diets, performing two-a-day training without glycogen restoration between sessions, and a "sleep-low" approach entailing a glycogen-depleting session in the evening without consuming CHO until after a morning training session performed in an overnight fasted state. Each of these methods can confer beneficial metabolic adaptations for the endurance athlete including increases in mitochondrial enzyme activity, mitochondrial content, and rates of fat oxidation, yet data showing a direct performance benefit is still unclear.

Impact of Endurance Exercise Training in the Fasted State on Muscle Biochemistry and Metabolism in Healthy Subjects: Can These Effects be of Particular Clinical Benefit to Type 2 Diabetes Mellitus and Insulin-Resistant Patients?

Exercise training intervention is a cornerstone in the care of type 2 diabetes mellitus (T2DM) and insulin resistance (IR), and it is pursued in order to optimize exercise interventions for these patients. In this regard, the nutritional state of patients during exercise (being in the fed or fasted state) can be of particular interest. The aim of the present review is to describe the impact of endurance exercise (training) in the fasted versus fed state on parameters of muscle biochemistry and metabolism linked to glycemic control or insulin sensitivity in healthy subjects. From these data it can then be deduced whether exercise training in the fasted state may be relevant to patients with T2DM or IR. In healthy subjects, acute endurance exercise in the fasted state is accompanied by lower blood insulin and elevated blood free fatty acid concentrations, stable blood glucose concentrations (in the first 60-90 min), superior intramyocellular triacylglycerol oxidation and whole-body lipolysis, and muscle glycogen preservation. Long-term exercise training in the fasted state in healthy subjects is associated with greater improvements in insulin sensitivity, basal muscle fat uptake capacity, and oxidation. Therefore, promising results of exercise (training) in the fasted state have been found in healthy subjects on parameters of muscle biochemistry and metabolism linked to insulin sensitivity and glycemic control. Whether exercise training intervention in which exercise sessions are organized in the fasted state may be more effective in improving insulin sensitivity or glycemic control in T2DM patients and insulin-resistant individuals warrants investigation.

The effect of carbohydrate mouth rinse on performance, biochemical and psychophysiological variables during a cycling time trial: a crossover randomized trial

BACKGROUND

The hypothesis of the central effect of carbohydrate mouth rinse (CMR) on performance improvement in a fed state has not been established, and its psychophysiological responses have not yet been described. The aim of this study was to evaluate the effect of CMR in athletes fed state on performance, biochemical and psychophysiological responses compared to ad libitum water intake.

METHODS

Eleven trained male cyclists completed a randomized, crossover trial, which consisted of a 30 km cycle ergometer at self-selected intensity and in a fed state. Subjects were under random influence of the following interventions: CMR with a 6% unflavored maltodextrin solution; mouth rinsing with a placebo solution (PMR); drinking "ad libitum" (DAL). The time for completion of the test (min), heart rate (bpm) and power (watts), rating of perceived exertion (RPE), affective response, blood glucose (mg/dL) and lactate (mmol/DL), were evaluated before, during and immediately after the test, while insulin (uIL/mL), cortisol (μg/dL) and creatine kinase (U/L) levels were measured before, immediately after the test and 30 min after the test.

RESULTS

Time for completion of the 30 km trial did not differ significantly among CMR, PMR and DAL interventions (means = 54.5 ± 2.9, 54.7 ± 2.9 and 54.5 ± 2.5 min, respectively; p = 0.82). RPE and affective response were higher in DAL intervention (p < 0.01). Glucose, insulin, cortisol and creatine kinase responses showed no significant difference among interventions.

CONCLUSIONS

In a fed state, CMR has not caused metabolic changes, and it has not improved physical performance compared to ad libitum water intake, but demonstrated a possible central effect. ReBec registration number: RBR-4vpwkg. Available in http://www.ensaiosclinicos.gov.br/rg/?q=RBR-4vpwkg.

Carbohydrate Mouth Rinse Fails to Improve Four-Kilometer Cycling Time Trial Performance

We investigated if a carbohydrate (CHO) mouth rinse may attenuate global fatigue and improve 4-km cycling time trial (TT_4km) performance. After a preliminary session, cyclists (n = 9) performed a TT_4km after a CHO or placebo (PLA) mouth rinse. Mean power output, time, and ratings of perceived exertion (RPE) were recorded throughout the TT_4km. Twitch interpolation responses (%VA; voluntary activation and ∆Tw; delta peak twitch torque) were compared pre and post TT_4km with traditional statistics and effect size (ES) analysis. Time-to-complete the 4 km and mean power output were comparable between CHO (386.4 ± 28.0 s) and PLA (385.4 ± 22.4 s). A lower central (p = 0.054) and peripheral (p = 0.02) fatigue in CHO than in PLA were suggested by an extremely-large ES in %VA (manipulation main effect: p = 0.052, d = 1.18; manipulation-by-time interaction effect: p = 0.08, d = 1.00) and an extremely, very-large ES in ∆Tw (manipulation main effect: p = 0.07, d = 0.97; time-by-manipulation interaction effect: p = 0.09, d = 0.89). The RPE increased slower in CHO than in PLA (p = 0.051; d = 0.7). The apparent reduction in global fatigue (central and peripheral) and RPE_SLOPE with only one CHO mouth rinse were not translated into improved TT_4km performance. Further tests may be required to verify if these likely differences in global fatigue might represent an edge in the short-lasting cycling time trial performance.

Regulation of Muscle Glycogen Metabolism during Exercise: Implications for Endurance Performance and Training Adaptations

Since the introduction of the muscle biopsy technique in the late 1960s, our understanding of the regulation of muscle glycogen storage and metabolism has advanced considerably. Muscle glycogenolysis and rates of carbohydrate (CHO) oxidation are affected by factors such as exercise intensity, duration, training status and substrate availability. Such changes to the global exercise stimulus exert regulatory effects on key enzymes and transport proteins via both hormonal control and local allosteric regulation. Given the well-documented effects of high CHO availability on promoting exercise performance, elite endurance athletes are typically advised to ensure high CHO availability before, during and after high-intensity training sessions or competition. Nonetheless, in recognition that the glycogen granule is more than a simple fuel store, it is now also accepted that glycogen is a potent regulator of the molecular cell signaling pathways that regulate the oxidative phenotype. Accordingly, the concept of deliberately training with low CHO availability has now gained increased popularity amongst athletic circles. In this review, we present an overview of the regulatory control of CHO metabolism during exercise (with a specific emphasis on muscle glycogen utilization) in order to discuss the effects of both high and low CHO availability on modulating exercise performance and training adaptations, respectively.

Impact of carbohydrate mouth rinsing on time to exhaustion during Ramadan: A randomized controlled trial in Jordanian men

Mouth rinsing using a carbohydrate (CHO) solution has been suggested to improve physical performance in fasting participants. This study examined the effects of CHO mouth rinsing during Ramadan fasting on running time to exhaustion and on peak treadmill speed (V_peak). In a counterbalanced crossover design, 18 sub-elite male runners (Age: 21 ± 2 years, Weight: 68.1 ± 5.7 kg, VO_2max: 55.4 ± 4.8 ml/kg/min) who observed Ramadan completed a familiarization trial and three experimental trials. The three trials included rinsing and expectorating a 25 mL bolus of either a 7.5% sucrose solution (CHO), a flavour and taste matched placebo solution (PLA) for 10 s, or no rinse (CON). The treatments were performed prior to an incremental treadmill test to exhaustion. Three-day dietary and exercise records were obtained on two occasions and analysed. Anthropometric characteristics were obtained and recorded for all participants. A main effect for mouth rinse on peak velocity (V_peak) (CHO: 17.6 ± 1.5 km/h; PLA: 17.1 ± 1.4 km/h; CON: 16.7 ± 1.2 km/h; P < .001, η_p² = 0.49) and time to exhaustion (CHO: 1282.0 ± 121.3 s; PLA: 1258.1 ± 113.4 s; CON: 1228.7 ± 98.5 s; P = .002, η_p² = 0.41) was detected, with CHO significantly higher than PLA (P < .05) and CON (P < .05). Oxygen consumption, heart rate, respiratory exchange ratio, and rating of perceived exertion were not significantly different between treatments or trials (P > .05). Energy availability from dietary analysis, body weight, and fat-free mass did not change during the last two weeks of Ramadan (P > .05). This study concludes that carbohydrate mouth rinsing improves running time to exhaustion and peak treadmill speed under Ramadan fasting conditions.

Carbohydrate Mouth Rinsing Does Not Prevent the Decline in Maximal Strength After Fatiguing Exercise

Black, CD, Schubert, DJ, Szczyglowski, MK, and Wren, JD. Carbohydrate mouth rinsing does not prevent the decline in maximal strength after fatiguing exercise. J Strength Cond Res 32(9): 2466-2473, 2018-Carbohydrate (CHO) rinsing has been shown to attenuate the decline of maximal voluntary contractions (MVCs) after fatiguing exercise-perhaps through a central mechanism. This study sought to determine the effect of a CHO rinse on MVC, voluntary activation, and contractile properties after fatiguing exercise. Thirteen adults participated in a double-blind, cross-over study. Maximal voluntary contraction of the dominant knee extensors was assessed, and voluntary activation (%VA) was determined using twitch interpolation. Participants then held 50% of MVC until volitional fatigue followed by a 20-second rinse with a solution of 8% maltodextrin (CHO) or placebo (PLA). Maximal voluntary contraction and %VA were reassessed immediately and 5 minutes after exercise. Maximal voluntary contraction did not differ between the CHO and PLA conditions initially (230 ± 90 vs. 232 ± 90 N·m; p = 0.69). Maximal voluntary contraction declined after exercise (p ≤ 0.01), but no differences were found between the CHO and PLA conditions (p ≥ 0.59). %VA did not differ between conditions (91.9 ± 2.9% vs. 91.5 ± 3.8%; p ≥ 0.11) nor did it change after exercise (p = 0.57). Twitch torque, rate of torque development, and rate of torque relaxation were reduced after exercise (p ≤ 0.05) but were unaffected by CHO rinsing (p > 0.05). Unlike a previous study, a CHO rinse did not preserve MVC after fatiguing exercise. This was likely due to a lack of central fatigue induced by the exercise protocol (as %VA was unaffected) as the CHO rinse is thought to work through a central mechanism.