Circadian rhythm–dependent effects of acute caffeine consumption on hydration and performance in football players

The aim of this study was to investigate the effects of acute caffeine (CAF) consumption at different time-of-day, in relation to circadian rhythm, on selected performance parameters and hydration status in football players, as well as to assess gastrointestinal responses following CAF intake. The study included twelve trained male football players aged between 18-25 years. Within the experimental design, which employed a randomized, single-blind approach, the familiarization session was conducted on the first day, followed by three separate test days. Sixty minutes before the initiation of testing, the football players ingested CAF at a dose of 6 mg/kg⁻¹. The tests, measurements, and analyses were conducted at 10:00 a.m. on day 1, 14:00 p.m. on day 2, and 18:00 p.m. on day 3. Differences between variables were analyzed using repeated-measures ANOVA. No significant difference was found in vertical jump, anaerobic power, change of direction (COD), 10 and 20m sprint, ball speed, rating of perceived exertion (RPE), and visual analogue scale (VAS) between time-of-day after CAF intake (p>0.05). There were significant main effects for the 30m sprint between time-of-day after CAF intake (p<0.05). CAF intake did not induce a significant difference in hydration levels (p>0.05). There was a significant difference in the Gastrointestinal Symptom Rating Scale (GSRS) total between the time-of-day after CAF intake (p<0.05). In conclusion, this study revealed that acute CAF intake in relation to circadian rhythm had no significant effect on performance in football players. Additionally, the findings indicated a slight decline in performance during the morning hours. This outcome is thought to be primarily attributable to the athletes’ habitual training and competition schedules rather than to CAF intake. Furthermore, gastrointestinal symptoms associated with morning CAF intake may have contributed to the observed performance decrease. Overall, the data suggested a tendency toward more favorable outcomes in the evening measurements.