Abstract
Background/Objectives: Consumption of New Zealand blackcurrant extract for 7 days has shown to reduce slowing of sprint speed in recreationally active males. Acute caffeine consumption has shown to improve repeated-sprint performance in a fatigued state. Thus, combined intake of New Zealand blackcurrants and caffeine may provide an additive or a synergistic effect to improve repeated-sprint performance, especially in fatigued individuals. Our study investigated the individual and additive effect of acute intake of New Zealand blackcurrant powder and caffeine on high-intensity intermittent running performance. Methods: Fourteen recreationally active males participated in a double-blind, randomised controlled crossover trial consisting of four experimental arms: placebo (PLA), New Zealand blackcurrant powder (NZBP), caffeine (CAFF), and NZBP + caffeine (NZBP + CAFF). Participants reported to the laboratory fasted and consumed a standardised breakfast with the study intervention 1 h before the exercise trial. Speed and distance covered for walking, sprinting, running, and jogging were assessed using the modified Loughborough Intermittent Shuttle Test (m-LIST). Blood lactate and free fatty acids (FFAs) levels, and perceptual measures (feeling scale, felt arousal scale and ratings of perceived exertion) were also assessed. Results: Caffeine intake increased average sprint speed (p = 0.045, η2 = 0.345) and reduced sprint time (p = 0.030, η2 = 0.463) during the m-LIST protocol. Ratings of perceived exertion were lower with caffeine intake (p = 0.014, η2 = 0.381), while blood lactate concentration was higher (p = 0.001, η2 = 0.761). Serum free fatty acids concentrations increased over time (p < 0.001, η2 = 0.900), with a significant NZBP × time interaction (p = 0.005, η2 = 0.433). No significant effects of NZBP alone or caffeine × NZBP interactions were observed for sprint performance outcomes. Conclusions: Acute NZBP did not improve repeated-sprint performance, either alone or when combined with caffeine. In contrast, caffeine-containing treatments were associated with improved sprint performance and lower perceived exertion. These findings suggest that caffeine, rather than NZBP, was responsible for the observed ergogenic responses, with no evidence of an additive benefit from acute combined supplementation.