Acute effects of beetroot juice and caffeine co-ingestion during a team-sport-specific intermittent exercise test in semi-professional soccer players: a randomized, double-blind, placebo-controlled study

Background Beetroot juice (BJ) and caffeine (CAF) are considered as ergogenic aids among athletes to enhance performance, however, the ergogenic effects of BJ and CAF co-ingestion are unclear during team-sport-specific performance. This study aimed to investigate the acute effects of BJ and CAF co-ingestion on team-sport-specific performance, compared with placebo (PL), BJ, and CAF alone. Method Sixteen semi-professional male soccer players (age: 19.8 ± 2.2 years, body mass: 69.2 ± 6.1 kg, height: 177.3 ± 6.0 cm) completed four experimental trials using a randomized, double-blind study design: BJ + CAF, CAF + PL, BJ + PL, and PL + PL. Countermovement jump with arm swing (CMJAS) performance and cognitive function by Stroop Word-Color test were evaluated before and after the Yo–Yo Intermittent Recovery Test level 1 (YYIR1). Also, rate of perceived exertion (RPE), heart rate, and gastrointestinal (GI) discomfort were measured during each session. Results No significant differences were shown between test conditions for total distance covered in YYIR1 (BJ + CAF: 1858 ± 455 m, CAF + PL: 1798 ± 422 m, BJ + PL: 1845 ± 408 m, PL + PL 1740 ± 362 m; p = 0.55). Moreover, CMJAS performance, cognitive function, and RPE during the YYIR1 were not significantly different among conditions ( p > 0.05). However, the average heart rate during the YYIR1 was higher in CAF + PL compared to PL + PL (by 6 ± 9 beats/min; p < 0.05), and GI distress was greater in BJ + CAF compared to PL + PL (by 2.4 ± 3.6 a.u.; p < 0.05). Conclusion These results suggest, neither acute co-ingestion of BJ + CAF nor BJ or CAF supplementation alone significantly affected team-sport-specific performance compared to the PL treatment.