Dietary Nitrate Supplementation Enhances Performance and Speeds Muscle Deoxyhaemoglobin Kinetics during an End-Sprint after Prolonged Moderate-Intensity Exercise

Short-term dietary nitrate (NO ₃ ⁻) supplementation has the potential to enhance performance during submaximal endurance, and short-duration, maximal-intensity exercise. However, it has yet to be determined whether NO ₃ ⁻ supplementation before and during submaximal endurance exercise can improve performance during a short-duration, maximal-intensity end-sprint. In a randomised, double-blind, crossover study, 9 recreationally active men ingested NO ₃ ⁻-rich (BR: 8 mmol NO ₃ ⁻/day) and NO ₃ ⁻-depleted (PL: 0.75 mmol NO ₃ ⁻/day) beetroot powder for 7 days. On day 7, participants completed 2 h of moderate-intensity cycling, which immediately transitioned into a 60 s maximal-intensity end-sprint, with supplements ingested 2 h before and 1 h into the moderate-intensity exercise bout. Plasma [NO ₃ ⁻] and [NO ₂ ⁻] were higher in BR compared to PL pre- and post-exercise (p < 0.05). Post-exercise plasma [NO ₃ ⁻] was higher than pre-exercise (562 ± 89 µM vs. 300 ± 73 µM; p < 0.05) and plasma [NO ₂ ⁻] was not significantly different pre- (280 ± 58 nM) and post-exercise (228 ± 63 nM) in the BR condition (p > 0.05). Mean power output during the final 30 s of the end-sprint was greater after BR (390 ± 38 W) compared to PL (365 ± 41 W; p < 0.05). There were no differences between BR and PL in any muscle oxygenation variables during moderate-intensity cycling (p > 0.05), but muscle [deoxyhaemoglobin] kinetics was faster during the end-sprint in BR (6.5 ± 1.4 s) compared to PL (7.3 ± 1.4 s; p < 0.05). These findings suggest that NO ₃ ⁻ supplementation has the potential to improve end-sprint performance in endurance events when ingested prior to and during exercise.