This study investigated the effect of caffeine contained in sports drink on hormones producing energy and sprint test performance in male soccer players. Twelve participants (25.97 ± 2.70 y) performed the test under thre e conditions (one week apart): caffeine with sports drink (SD-CAF), sports drink (SD), and placebo (PLA). Using a double-blind, placebo-controlled, randomized, crossover protocol, participants performed SD-CAF trial (5 mg/kg of caffeine contained in 300 ml of sports drink 30 minutes prior to sprinting test (7 × 30 m), SD trial (solely 300 ml of sports drink 30 minutes prior to sprinting test), or placebo. Blood analysis indicated significantly higher level of free thyroxine in SD-CAF (21.450 ± 3.048) compared to SD (18.742 ± 1.151) and PLA (16.983 ± 1.783). Similar findings existed regarding insulin (P < 0.05). However, DHEAs was significantly higher in PLA compared to SDCAF and SD. No statistical differences were observed between trials in testosterone and blood lactate (P > 0.05). No significant differences were observed between trials in first–fourth repetitions (P > 0.05). Time of fifth-seventh repetitions were significantly lower in SD-CAF compared to SD and PLA (P < 0.05), and were significantly lower
in SD than that in PLA (P < 0.05). The time of 7th repetition was (4.331 ± 0.210, 4.610 ± 0.197, 4.81 6 ± 0.171 s for SD-CAF, SD, and PLA, respectively; P < 0.05). In conclusion, caffeine interferes hormones that are responsible for producing energy which in turn have a positive effect on repeated sprint bouts.
Keywords: Caffeine, energy hormones, sports drink, thyroxine, testosterone