Document Type : Research Paper
Authors
1
Master's student in exercise physiology, Department of Exercise Science, Faculty of Humanities, Semnan University, Semnan, Iran
2
2. Associate Professor of Exercise Physiology, Department of Exercise Sciences, Faculty of Humanities, Semnan University, Semnan, Iran
3
Exercise Physiology, Department of Exercise Sciences, Faculty of Humanities, Semnan University, Semnan, Iran
Abstract
Extended Abstract
Background and Purpose
Exercise is widely recognized as a key factor enhancing fat oxidation and positively regulating metabolic processes in the body. This is particularly relevant during sports activities where the body mobilizes fat stores to meet energy demands. Caffeine, a prevalent physiological stimulant among athletes, contributes by increasing alertness, mitigating fatigue, and improving cognitive and physical performance. Recently, a novel method of caffeine administration—gargling with a caffeine-containing solution—has gained attention. This delivery route facilitates rapid absorption through the oral mucosa, potentially offering faster ergogenic effects compared to conventional oral ingestion such as caffeinated beverages. Understanding this method's side effects, absorption kinetics, and interactions with other nutrients remains limited. Furthermore, the impact of caffeine mouth rinsing and its dosage on fat oxidation and maximal oxygen consumption (VO2max) remains unclear amid conflicting evidence. Hence, this study aimed to examine the effects of caffeine mouth rinsing on fat oxidation and VO2max during exercise in young female athletes.
Materials and Methods
Participants: In the present study, 14 young female athletes majoring in physical education who voluntarily expressed their readiness to participate in this study through a call at Semnan University completed a consent form. To carry out the initial stages of the study, a personal information questionnaire and a health form were distributed and completed. Subjects were screened for lack of disease (including cardiovascular, respiratory, and musculoskeletal diseases), having a sports history (i.e., having at least three sessions of regular exercise per week for six months before the start of the study), and having a BMI less than 25.
Research Method: The research method was set up and implemented as a crossover and counterbalanced design. In the first phase of the study, a briefing session was held on a day other than the test day to educate and explain the procedure, and the subjects were familiarized with the procedure. They were asked not to consume caffeine 24 hours before the test and also not to have used steroid medications in the past two months. The exclusion criteria for subjects from the study were any physical or cognitive limitations (chronic illness, physical and mental disorders), use of energy supplements, and performance-enhancing substances. Participants were reminded of what foods and beverages were rich in caffeine and to avoid consuming them. Then, the subjects arrived at the laboratory at 7:30 AM on two different days, one week apart, after fasting for 12 hours. Seven of the subjects consumed caffeine and seven of them consumed placebo. One week later, the test was repeated, and participants who had received the caffeine the previous week were given a placebo, and those who had used the placebo were given a caffeine, and then the tests were repeated. The selection of supplement and placebo bottles was done and recorded by someone other than the researcher, and they were handed over to the researcher at the end of the study. The time of the subjects' attendance was determined based on the menstrual cycle in the luteal phase and according to the schedule specified for them.
Supplement consumption: Supplement consumption was carried out in a double-blind manner. People in the supplement group received an average dose of pure caffeine per kilogram of body weight (six milligrams per kilogram of body weight in 25 milliliters of water), on an empty stomach, one hour before exercise, as a mouth rinsing. The caffeine consumed in this study was Enercaff 200 caffeine capsules, with full observance of hygiene precautions and without any preservatives, and its manufacture was approved by the research ethics committee. The placebo group also received 25 ml of water. Also, 10 cc of peppermint extract was added to make the subjects unaware of the solutions they were consuming, which were similar in shape and color to the caffeine solution and water. In both conditions, they mouth rinsing their solutions for 20 seconds.
Exercise protocol: After a five-minute warm-up, the subjects were connected to a gas analyzer (Cortex, Germany, model MPU31-105) and they went on a treadmill. The activity began at a speed of 3.5 km/h and a 1% incline, and the treadmill speed was increased by 1 km/h every three minutes, until it reached a speed of 7.5 km/h. At this point, the speed remained constant and the incline of the device was increased by 2% every three minutes until the respiratory exchange ratio (RER) was equal to 1. Finally, the speed and incline were increased simultaneously until the fatigue threshold was reached (20). And the test data were displayed on the screen. The measurement was carried out by attaching a mouthpiece to the subject and recording the variables moment by moment using an open-circuit method and displayed on the computer screen. The pressure, temperature and humidity standardized with the variables were calculated by the device. The air and gas of the device were calibrated by a capsule containing standardized gases (O2 16% and CO2 4%) and the turbine of the device was calibrated by a three-liter syringe. Calibration was repeated at the beginning of each month. The temperature of the laboratory room was also measured by a gas analyzer (mean and standard deviation of ambient temperature: 27.46±1.18 and mean and standard deviation of ambient humidity: 45.91±1.17).
The aim of the final part of the test was to measure VO2max. The criteria for achieving VO2max were reaching a heart rate equal to or greater than 10 beats below maximum heart rate (calculated by age-220), no increase in oxygen consumption despite increasing activity intensity, and RER greater than 1.05. The average carbon dioxide exhaled (Vco2) and oxygen consumed (Vo2) in the last two minutes of each stage were calculated, and the rate of carbohydrate and fat oxidation was calculated using elemental equations, assuming negligible urinary nitrogen. Then, the MFO, FATmax, and crossover points (the point of relative activity intensity at which the relative contribution of carbohydrate exceeds that of fat) were determined.
Statistical analysis: In the present study, the Kolmogorov-Smirnov test was used to examine the normality of the data distribution. Also, the paired t-test was used to compare the variables. Statistical calculations were performed using SPSS version 24 software at a significance level of P≤0.05.
Findings
The Kolmogorov-Smirnov test confirmed data normality. Paired t-tests (SPSS v24) compared metrics between caffeine and placebo conditions at a significance threshold of P ≤ 0.05. Results indicated no significant differences in MFO (P=0.729) and VO2max (P=0.150) between conditions. FATmax approached significance (P=0.052) under caffeine gargling condition.
Crucially, time to exhaustion significantly improved with caffeine gargling (P=0.012). While fat oxidation rates showed a nonsignificant elevation in the caffeine condition, carbohydrate oxidation remained stable. These trends suggest a favorable influence of caffeine gargling on fat utilization.
Conclusion
This study demonstrates that gargling with caffeine solution does not significantly alter MFO, VO2max, or FATmax in young female athletes but does significantly prolong time to exhaustion. The ergogenic effect on endurance likely arises from central nervous system adenosine receptor inhibition and diminished perception of fatigue.
These findings highlight the potential utility of caffeine gargling for enhancing short-term endurance and neuromuscular efficiency. To elicit more pronounced metabolic effects, future research should explore optimal dosing and timing strategies. Accordingly, caffeine gargling may serve as a practical adjunct in athletes’ training regimens, particularly for individuals engaged in fasted training, those unable to ingest caffeine orally, or when time constraints limit intake options.
Keywords: Caffeinated Mouthwash, Fatigue, Maximal Fat Oxidation, Female Athletes.
Article Message
Gargling caffeine solution significantly enhances time to exhaustion without altering key metabolic markers of fat oxidation in female athletes. The ergogenic benefits likely stem from central nervous system modulation independent of peripheral metabolic changes. Differences in absorption dynamics between gargling and oral intake may account for observed effects.
Authors’ Contributions
All authors contributed to study design, implementation, data analysis, and manuscript drafting.
Conflicts of Interest
The authors declare no conflicts of interest regarding publication.
Acknowledgment
This research was self-funded. The authors extend sincere thanks to all participants for their cooperation.
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