Ingestion of dietary nitrate supplementation enhances athletic time trial performance but data on its effectiveness in trained female runners is limited. The purpose of this study was to investigate the effect of beetroot juice supplementation (BRJ) on 5 km running time trial performance compared to a placebo (PLA) and no supplementation (CON). Using a double-blind, repeated-measures crossover design with a 14 day washout period, 11 trained female runners (age 20±3 years, 52.6±4.6 mL.kg.min−1, body mass 53.0±3.9 kg, stature 164.2±5.8 cm) ingested 2×70 mL of either BRJ (∼8 mmoL·d−1 nitrate) or PLA for 4 days and 2.5 h before performing a 5 km time trial. Blood pressure (BP), mean heart rate (HR), post-test blood lactate (BLa), 5 km time trial and 1 km split times were assessed. No main effect was found for change in systolic BP (CON=122±8, PLA=120±7, BRJ=114±9 mm Hg), but trends towards reductions after BRJ were observed, BRJ vs CON -8 mm Hg (-10 to 5; 90% CI, ES=0.82) and BRJ vs PLA 6 mm Hg (9 to 2; 90% CI, ES=0.64). No main effect was found for 5 km time trial performance (CON=1287±126, PLA=1268±109, BRJ=1237±109 s) but trends towards reductions after BRJ were observed, BRJ vs CON −49 s (73 to −26; 90% CI, ES=0.44) and BRJ and PLA −31 s (−48 to −14; 90% CI, ES=0.30). 1 km split times were similar between conditions except for the 2nd km where BRJ was faster than CON by 16 s (−25 to −7; 90% CI and ES=0.61) and PLA by 12 s (20 to 4; 90% CI and ES=0.57). No between group differences were observed for mean HR (CON=182±8, PLA 181±7, BRJ=182±7 bpm−1; or post time trial BLa (CON=6.8±1.9, PLA=6.9±1.9, BRJ=6.9±1.9 mmol.L−1). Although not statistically significant, these results suggest BRJ supplementation improved 5 km time trial performance over PLA by 31 s (2.4%). Athletes should consider ingesting BRJ to improve 5 km running performance.
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