Carbohydrate rinsing modestly improved cycling performance

Carbohydrate mouth rinsing is a simple strategy that may help hard exercise feel a touch easier. This study tested whether that mouth signal could change effort and performance during a short cycling time trialA test where you cover a set distance (or set amount of work) as fast as you can. The score is your finish time. It mirrors real-world performance and is easy to compare over time., which makes it interesting for runners and coaches, but not immediately practical without caveats.

Reference: Park et al. Oral carbohydrate sensing enhances prefrontal cortex oxygenation, reduces perceived exertion, and improves high-intensity cycling performance: A randomized crossover trial. PLOS ONE (2026) DOI: https://doi.org/10.1371/journal.pone.0349067.

Study snapshot

A quick, practical summary for runners and coaches.

Quick answer

This 5-visit randomised crossover trialA study in which a group of people is randomised to receive BOTH the treatment and the no-treatment control, and the outcome of interest is measured before and after both. The “crossover” means that all participants complete all interventions (the control and the treatment), usually with a washout period in between. studied 11 trained cyclists. A carbohydrate mouth rinse modestly improved a short cycling time trial and lowered perceived effortRating of perceived exertion (RPE) is a simple way to score how hard exercise feels to you, not to a machine. You pick a number on a scale (often 1–10), where low numbers mean “this feels easy” and high numbers mean “I’m really pushing it.” It blends how heavy your breathing is, how tired your muscles feel, and how much effort you think you’re putting in.. The main caution is that the study was tiny, lab-based, and not done in runners.

Key takeaways

  • The carbohydrate mouth rinse produced a small performance benefit during a short, hard cycling test.
  • The study was small and only indirectly relevant to running.
  • Runners could test this in training, but it should not replace proper fueling.

How confident should we be?

Evidence confidence: Low

The crossoverCrossover means that all subjects completed all interventions (control and treatment) usually with a wash-out period in between. design was useful, and the researchers measured several relevant outcomes. But only 11 cyclists took part, the study was short and lab-based, and the findings need runner-specific replication.

Bottom line

Carbohydrate mouth rinsing may help some athletes feel slightly better during short, intense efforts. For marathon, trail, and ultra runners, it is a niche strategy to test, not a magic swill-and-spit shortcut to glory.

Read the deep dive below for a practical interpretation, actionable decisions, my thoughts, my Rating of Perceived scientific Enjoyment, the study details, full results, strengths, and limitations.

Running science research reviews for endurance runners

The deep dive

The details behind the headline result, including the practical meaning, full findings, limitations, and my interpretation.

Practical meaning

What does this research mean for runners and coaches?

This study was not a running study, so the practical meaning is an interpretation, not a direct study finding. The results are most relevant to short, hard efforts where perceived effort, attention, and pacing matter.

For runners

For road runners, the closest fit is a short race, a hard time trial, a track session, or the final few minutes of a race. For marathon runners, trail runners, and ultra runners, the study is less directly useful because longer races depend heavily on actual carbohydrate intake, hydration, pacing, heat management, and the quiet art of not making terrible decisions at mile 22.

A carbohydrate mouth rinse may be worth testing when swallowing fuel feels difficult, especially close to a hard effort. But it should not replace eating or drinking carbohydrate during longer events.

For coaches

Coaches could treat carbohydrate mouth rinsing as a low-cost strategy to trial during specific sessions. It may suit athletes who struggle with gut comfort before short, intense work, or athletes who want to practise a simple pre-effort routine.

The key word is “trial”. Test it in training, observe whether it helps, and avoid turning a small lab finding into a well-trained dogma.

Practical decision

Should runners change anything?

Maybe. Runners could test carbohydrate mouth rinsing in training before using it in a race, but it should not replace a proper fueling plan.

Consider this if

  • You are doing short, hard intervals or a short time trial.
  • You struggle to swallow carbohydrate close to intense exercise.
  • You want to test a simple, low-risk strategy during training.

Do not overreact if

  • You are preparing for a marathon, trail race, or ultra and still need a proper fueling plan.
  • You expect a mouth rinse to rescue poor pacing, poor training, or breakfast choices made during a spiritual crisis.

A sensible next step

Test a carbohydrate mouth rinse in training before using it in a race. The study used 25 millilitres of a 6.4% maltodextrin solution (dissolve 1.6 grams of maltodextrin in 25 millilitres of water), rinsed for 10 seconds and spat out, repeated 5 times before exercise. That is not a prescription for every runner, but it is a useful starting point for a controlled experiment.

TIP: Never make any major changes to your training or lifestyle habits based on the findings of one study, especially if the study is small or provides low-quality evidenceA low quality of evidence means that, in general, studies in this field have several limitations. This could be due to inconsistency in effects between studies, a large range of effect sizes between studies, and/or a high risk of bias (caused by inappropriate controls, a small number of studies, small numbers of participants, poor/absent randomisation processes, missing data, inappropriate methods/statistics). When the quality of evidence is low, there is more doubt and less confidence in the overall effect of an intervention, and future studies could easily change overall conclusions. The best way to improve the quality of evidence is for scientists to conduct large, well-controlled, high-quality randomised controlled trials.. Check whether other trials confirm the findings. If there is a meta-analysisA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all known studies of that treatment. on the topic, look at the effect sizeA standardised measure of the magnitude of an effect of an intervention. Unlike p-values, effect sizes show the size of the effect and how meaningful it might be. Common effect size measures include standardised mean difference (SMD), Cohen’s d, Hedges’ g, eta-squared, and correlation coefficients., the variability between studies, and the quality of evidenceCertainty of evidence tells us how confident we are that the published results accurately reflect the true effect. It’s based on factors like study design, risk of bias, consistency, directness, precision, and publication bias. High certainty means that the current evidence is so strong and consistent that future studies are unlikely to change conclusions. Whereas, low certainty means more doubt and less confidence, and that future studies could easily change current conclusions..

Expert interpretation

My thoughts

Running science from Thomas Solomon at Veohtu

The force is mildly strong with this one.

The researchers tested a clear question using a sensible crossover design, and the main performance outcome was practical: how quickly the cyclists completed a 4 km time trial. The carbohydrate mouth rinse improved completion time by about 2.7 seconds compared with placeboA dummy treatment that looks like the real one but has no active ingredient, or no active effect for the outcome being studied, and is used for fair comparison.. That is small, but in a short, hard effort, small can matter.

The brain-related results are interesting, too. The carbohydrate rinse increased oxygenation in a part of the brain linked with attention, decision-making, and effort control. The participants also reported lower effort. That pattern fits the idea that carbohydrate sensing in the mouth may influence how the brain regulates effort, even when the carbohydrate is not swallowed.

But the brakes need to stay on. The study included only 11 trained cyclists. And the researchers did not directly measure central fatigue with neuromuscular tests, so the mechanism remains plausible rather than nailed to the lab bench.

For runners, the sensible message is don't “rinse your way to glory” but consider testing carbohydrate mouth rinsing for short, hard efforts or moments when swallowing fuel is awkward. Mouth rinsing should not become a replacement for proper race nutrition. The mild triumph is that a simple mouth signal may slightly reduce the mental cost of hard exercise. That said, endurance athletes shouldn't overinflate a tiny marginal gain.

My Rating of Perceived scientific Enjoyment

owlRPsE: 5/10

I experienced low to moderate scientific enjoyment because the crossover design, clear protocol, meaningful performance outcome, and transparent conflict reportingA conflict of interest happens when a person or group has a personal, financial, or professional interest that could influence their judgment. It does not always mean they did something wrong. But it can create bias or make others question whether the decision or result is fully fair and trustworthy. made the study scientifically satisfying. The buzzkill is that the sample was tiny, partly unblindedBlinding is when people in a study don’t know which treatment they’re getting. It stops expectations or beliefs (from patients or researchers) from skewing the results. “Single-blind” means participants don’t know; “double-blind” means participants and researchers don’t know; “triple-blind” means that the participants, researchers, and data analysts are kept in the dark. The goal is simple: fair tests and trustworthy findings., and only indirectly useful for runners.

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Read on for further details about the paper.

Research question

What did the researchers ask?

The authors aimed to test whether carbohydrate mouth rinsing or music listening affected brain oxygenation, cognitive performance, perceived effort, and cycling performance during a short, high-intensity cycling time trial.

Put more simply, the researchers asked whether a carbohydrate signal in the mouth could reduce effort and improve performance without the athlete swallowing the carbohydrate.

Study design

What type of study was this?

This study was a randomizedRandomization means assigning people to different parts of a study (e.g., groups in a randomised controlled trial) by chance, not by choice. This helps make the groups similar at the start and reduces bias, so any differences you see are more likely due to the treatment, not background differences. In a crossover study, randomization usually decides the order in which each person gets the treatments (for example, Treatment A first then B, or B first then A). This way, order effects—like learning, fatigue, or simple time passing—are less likely to skew the results., single-blind, crossover trial.

A randomized crossover trial can test whether an intervention caused a change under the study conditions because each participant completes each condition. That helps reduce the problem of comparing different people with different fitness levels, pacing habits, and pain faces.

But the design does not tell us whether the same thing would happen in runners, in longer races, or outside the lab. It also cannot fully blind the music condition because, rather inconveniently, most people can tell when music is playing.

Participants

Who took part?

The study included 11 trained cyclists: 7 men and 4 women.

The participants trained in cycling at least 5 days per week, had at least 2 years of endurance cycling training, and reported an average training volume of about 4 hours per day.

The researchers excluded people with cardiovascular, neurological, or metabolic disorders, and people taking medications that could affect cardiovascular or cognitive function.

Methods

What did the researchers do?

Who? 11 trained cyclists
What? Carbohydrate mouth rinse, music listening, and placebo mouth rinse
How long? 5 laboratory visits

The participants completed 5 laboratory visits. The first visit included screening, body measurements, and a cycling test to estimate fitness. The second visit familiarized the participants with the time trial, mouth-rinse procedures, brain oxygenation measurement, and cognitive test.

The final 3 visits were the experimental trials. Each cyclist completed 3 conditions in randomized and counterbalanced order: carbohydrate mouth rinse, music listening, and placebo mouth rinse. The trials were separated by 3 to 7 days.

For the carbohydrate mouth rinse, the participants rinsed their mouth with 25 mL of a 6.4% maltodextrin solution for 10 seconds, then spat it out. They completed 5 rinses, separated by 30 seconds. The placebo rinse used distilled water with a small amount of non-caloric sucralose to mimic subtle sweetness.

The music condition involved listening to 120 beats per minute music for 15 minutes through standardized earbuds.

The researchers measured oxygenation in the dorsolateral prefrontal cortex using functional near-infrared spectroscopy (NIRS)A non-invasive method that uses light to estimate how much oxygen is in a body tissue, such as muscle or brain. In exercise studies, researchers often use it to track how well working muscles receive and use oxygen.. In plain English, this uses light sensors placed on the head to estimate changes in blood oxygenation in the brain.

The participants also completed a Stroop testA test of attention and mental control. People usually name the color of a word while ignoring what the word says, which gets harder when the two do not match., which measures attention and response control. During the 4 km cycling time trial, the researchers measured completion time, power output, speed, perceived effort every 500 m, heart rate, and blood lactate.

Main findings

What did the study find?

4 km completion time Small improvement
Perceived effort Lower with carbohydrate rinse
Heart rate and lactate No clear difference

The carbohydrate mouth rinse increased oxygenation in both sides of the dorsolateral prefrontal cortex compared with music listening and placebo. This was seen immediately after the intervention and after the 4 km time trial. The dorsolateral prefrontal cortex is involved in attention, decision-making, and effort control.

The carbohydrate mouth rinse was also linked with better Stroop test performance after the time trial. The participants did not differ between conditions before the exercise test, but after the time trial, their cognitive performance was better after the carbohydrate rinse than after music or placebo.

The carbohydrate mouth rinse lowered perceived effort. The cyclists reported lower effort after the carbohydrate mouth rinse than after placebo at all measured distance points during the time trial. The carbohydrate rinse also lowered effort compared with music during the middle part of the trial. Music did not lower perceived effort compared with placebo.

The performance effect was statistically significantEvidence that a result is unlikely to be due to chance under a “no effect” model (or null hypothesis). Statistical significance is often judged by a p-value below 0.05 to flag that “something” is going on, but not how big or important that “something” is. One statistically significant result doesn’t mean proof; replication is needed. And, a statistically significant result doesn’t necessarily indicate clinical significance. but small. The average 4 km completion time was 336.64 seconds with the carbohydrate mouth rinse, 339.43 seconds with music, and 339.36 seconds with placebo. So, the carbohydrate rinse improved time by about 2.7 seconds compared with placebo, or about 0.8%.

MeanThe average of a set of numbers, calculated by summing all the values and dividing by the total number of values. power output was higher with the carbohydrate rinse than with music, but not clearly higher than with placebo. Mean speed was higher with the carbohydrate rinse than with placebo. Peak power did not differ between conditions.

Heart rate and blood lactate did not differ between conditions. This supports the idea that the effect was not explained by measured peripheral physiological changes. However, the study did not rule out subtle peripheral effects that heart rate and lactate measurements may have missed.

The authors concluded that carbohydrate mouth rinsing increased prefrontal cortex oxygenation, preserved executive function, reduced perceived effort, and modestly improved short high-intensity cycling performance without detectable differences in heart rate or blood lactate.

What helps my confidence in the findings?

The strengths

  • The crossover design meant each cyclist completed all 3 conditions.
  • The condition order was randomized and counterbalanced.
  • The researchers used a placebo mouth rinse and tried to preserve blinding between the rinse conditions.
  • The study measured performance, perceived effort, cognitive performance, brain oxygenation, heart rate, and blood lactate.
  • The researchers adjusted the analyses for period, sequence, and carryover effects.

What limits my confidence in the findings?

The limitations

  • The study was very small, with only 11 participants.
  • The required sample was 14 completers, and the researchers targeted 15 to allow for attrition, but only 11 completed the study.
  • The trial was registered retrospectively, and the researchers changed the original protocol by removing the mental fatigue task and dropping planned functional connectivity analyses.
  • The music condition could not be blinded, there was no matched sham music control, and the music comparisons should be treated as exploratory.
  • The researchers did not perform a formal check to see whether participants guessed the mouth-rinse condition correctly.
  • The study tested trained cyclists during a short cycling time trial, not runners during road, trail, or ultra events.
  • The researchers did not directly measure central fatigue using neuromuscular tests.
  • The participants had real-time performance feedback during the time trial, which may have influenced pacing.

Funding and conflicts

Who funded the study?

The study was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea.

The authors declared no competing interests. That lowers concern about commercial bias, especially because no mouth-rinse manufacturer appears to have funded the study. Still, the small sample sizeN is how many participants or observations are analyzed. A bigger N usually means more precise estimates and more power (ability to detect a true effect). A smaller N results in a study that is less likely to detect a true effect (false negative/type II error) and is more likely to report false positives (type I error). Of course, a badly designed study is still bad even if it has a big N. and lab-based design remain more important limitations than funding.

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