The purpose of this study is to investigate the additive effects of creatine and caffeine on changes in the cardiorespiratory system, metabolism, and performance of soccer players. Seventeen male soccer players randomly ingested three sports drinks comprising the following: glucose−electrolyte-based (Drink 1, control; D1), glucose−electrolyte-based drink + 5 g creatine (Drink 2; D2), and glucose−electrolyte-based drink + 5 g creatine + 35 mg caffeine (Drink 3; D3) during a 15 min recovery period after the modified Loughborough Intermittent Shuttle Test (LIST) on a standard outdoor soccer field. Then, a 20-m repeated intermittent sprinting activity was performed. The results showed no significant differences in cardiorespiratory and gas exchange variables. The non-significant levels of blood glucose concentrations among drinks with higher blood lactate concentrations were detected in parallel with increased heart rate during intermittent sprinting as a result of exercise intensities. Significantly longer sprinting time was found in D3 than D1 (p < 0.05), with no significant differences between D2 and D3. From this study, we conclude that the additive effect of caffeine−creatine supplements in a glucose−electrolyte drink during the 15 min recovery period enhances repeated 20-m high-intensity running in soccer players with no negative effect on cardiorespiratory functions.
Keywords: caffeine; creatine; isocaloric supplement; soccer performance; sports drink; sprinting time.