Effects of carbohydrate, caffeine, and combined mouth rinses on physiological and perceptual responses during high-intensity interval exercise following a pre-exercise meal: a double-blinded, placebo-controlled, randomized crossover trial.

Background: Mouth rinsing with carbohydrate (CHO), caffeine (CAF), and their combined (CHO+CAF) solutions has been shown to enhance exercise performance. However, most previous studies were conducted under fasted conditions, which may not accurately reflect the typical practices of athletes who generally consume food before intense exercise or competition. This study examined the effects of CHO, CAF, and CHO+CAF mouth rinses on physiological and perceptual responses during high-intensity interval exercise (HIIE) following a pre-exercise meal.

Methods: Twelve recreationally active males (age: 23.4 ± 3.2 years) completed four HIIE trials involving 8 bouts of 1-min cycling at 85% of peak power output (PPO), separated by 1-min active recovery at 20% of PPO. Using a double-blinded randomized crossover design, participants rinsed with either 10% maltodextrin (CHO), 1.2% caffeine (CAF), 10% maltodextrin + 1.2% caffeine (CHO+CAF), or water (PLA) twice in each trial (after warm-up and interval 4). All solutions were taste-matched using the artificial sweetener sucralose. A standardized CHO-rich (1 g·kg^-1 body weight) breakfast was provided an hour before testing.

Results: Ratings of perceived exertion were significantly different between conditions after interval 4 (CHO: 12.3 ± 1.6; CAF: 13.5 ± 2.2; CHO+CAF: 12.7 ± 1.7; PLA: 13.7 ± 2.4; $p$ = 0.049, ${\eta }_p^2$ = 0.21), but no significant effects of the mouth rinse conditions were observed on heart rate, blood glucose, blood lactate, affective valence, perceived activation, or affective responses (pleasure, arousal, and dominance) (all p > 0.05).

Conclusion: These findings suggest a limited ergogenic benefit of CHO and/or CAF mouth rinse through physiological and perceptual responses following sufficient food intake.