Introduction The aim of the study was to assess the effect of caffeine and caffeine with guarana on the dehydration of young soccer players and the effect of dehydration on their reaction time.
Material and Methods The study involved 57 players aged 16.8 ± 0.5 years, with an average body weight of 66.5 ± 9.3 kg, and height 178 ± 6.7 cm. An analysis of the body composition was performed. Thus, the results regarding body weight, adipose tissue, muscle tissue, BMI and body hydration were obtained. Next, the competitors performed successively a test for reaction time and speed over a distance of 5 and 15 meters with the use of photocells. After the tests, the players were randomized into 3 groups, where they received 200 mg caffeine, caffeine + guarana (200 mg + 40 mg), and placebo. Then, the players participated in a soccer training of medium intensity on the pitch, which lasted about 60 minutes. Immediately after completing the training, the procedure for testing reaction time and speed as well as body composition analysis were repeated.
Results Water loss occurred in each of the study groups and was the highest in players consuming caffeine with guarana and caffeine, but these were not statistically significant differences compared to placebo. Lower BMI correlated with water loss; however, statistically significant differences were noticed only in the placebo group (p ---lt--- 0.001). Water loss also correlated with a smaller decrease in speed over a distance of the 5-meter sprint (p ---lt--- 0.039) and the 15-meter sprint (p ---lt--- 0.035), but only in the caffeine-guarana group.
Conclusions Caffeine consumption in the amount of about 3 mg/kg of body weight and also caffeine with guarana did not result in significantly greater loss of water in young soccer players. The loss of water during training in players was almost 0.7 l and did not affect the reaction time. The obtained results are important in the context of consuming supplements based on caffeine and guarana for young footballers in order to improve parameters such as speed or reaction time. However, it is also worth conducting research on a group of adult players.
