Carbohydrate mouth rinsing during an intermittent fasting has been reported to be advantageous for endurance performance; however, there appears to be no clear effect on repeated sprints. What has not been investigated previously is the effects of combined caffeine and carbohydrate (CAF-CHO) mouth rinsing on speed-endurance performance commonly performed by track and field athletes during a fasted state. PURPOSE: To determine the influence of CAF-CHO mouth rinsing on sprinting kinetics and kinematics, as well as subjective exertion during a speed-endurance bout performed in a fasted state. METHOD: In a counterbalanced, single-blind random order design, eleven (n = 11) well-trained National level male sprinters and middledistance runners performed three 15-sec all-out sprints on a Woodway nonmotorized force treadmill, interspersed with 2-min active recovery between sprints. Athletes rinsed 25 ml of CAF-CHO (4g carbohydrate, 5 mg caffeine), or a similarly coloured placebo solution (PLA) prior to warm-up (30-min pre-trial), 1-min pre-trial, and the mid-way of each period of active recovery. On one occasion, no mouth rinse (NMR) was administered. The study was conducted within the second and third quarters of Ramadan, and each session separated by at least 72 hours. RESULTS: At the start of each trial, the rating of perceived exertions (RPE), readiness to train, blood glucose, and lactate concentrations were similar (p > 0.05). A significant primary effect of trial (3 x 15 seconds sprint) was observed for the distance (p = 0.019), revealing a longer average distance achieved in the CAF-CHO compared to PLA trial (69.80 + 3.57 vs. 68.08 + 3.22; p = 0.026; EF: 0.5), and NMR (69.69 + 3.82; p = 0.680; EF: 0.2). The difference between NMR and PLA also approached significance (p = 0.073; ES: 0.5). The CAF-CHO intervention also obtained better results in all other sprint measures such as average velocity, peak acceleration, and peak horizontal force, although these differences were not significant. Post-trial RPE was higher during NMR (7.23 + 1.92) as compared to CAF-CHO (6.54 + 2.15) and PLA (6.38 + 1.94) (p = 0.247). CONCLUSION: In challenging metabolic conditions, CAF-CHO mouth rinsing might have potential to improve measures of sprint training performance with a positive ergogenic effect on speed endurance performance