Author(s): ZHANG, J., DAI, Z., POON, E.T., WONG, S.H., Institution: THE CHINESE UNIVERSITY OF HONG KONG, Country: HONG KONG, Abstract-ID: 545

INTRODUCTION:
Nitric oxide (NO) plays a critical role in improving mitochondrial efficiency and muscle contractile efficiency during exercise and can be exogenously increased via nitrate supplementation. While numerous studies have investigated the effects of nitrate supplementation on exercise performance, most literature has focused on endurance-based exercise protocols. Meanwhile, the optimal dose of nitrate supplementation to maximize performance benefits during high-intensity interval exercise remains unclear, as previous studies have utilized a wide range of nitrate doses and predominantly recruited male participants, overlooking potential sex differences in responses to nitrate supplementation. Therefore, this study aimed to investigate the acute effects of various doses of nitrate-rich beetroot juice on the responses to high-intensity interval cycling in women.
METHODS:
A double-blinded, randomized, placebo-controlled, crossover trial was conducted with 13 recreationally active young women (age = 23 ± 2 years). All participants performed interval exercise (8 × 1-min bouts of cycling at 85 % of peak power output [PPO] interspersed with 1-min active recovery at 20% of PPO) 2.5 h after consumption of the randomly assigned beetroot juice containing 0 mmol (placebo control group [PLA]), 6.45 mmol (single-dose group [SIN]), or 12.9 mmol (double-dose group [DOU]) nitrates. The heart rate (HR), blood pressure, blood lactate, blood glucose, oxygen saturation, rating of perceived exertion (RPE), and emotional arousal were assessed. All data collected during the interval exercises were analyzed using a two-way (treatment × time) repeated-measures ANOVA to explore the effect of interventions (PLA, SIN, and DOU) over time on the magnitude of each dependent variable. Statistical significance was set at p < 0.05.
RESULTS:
Nitrate supplementation significantly altered the HR and RPE responses across the three trials. The mean HR was lower in the SIN and DOU groups than in the PLA group during both work intervals (F[1.90, 195.78] = 7.06, p = .001, η_p^2 = .064) and recovery periods (F[2, 180] = 9.89, p < .001, η_p^2 = .099), as well as across the overall protocol (F[1.93, 374.47] = 16.90, p < .001, η_p^2 = .080). The mean RPE was lower in the SIN and DOU groups than in the PLA group during recovery periods (F[2, 180] = 10.39, p < .001, η_p^2 = .104) and across the overall protocol (F[2, 388] = 11.96, p < .001, η_p^2 = .058). However, there was no significant difference in either HR or RPE between SIN and DOU on any endpoint.
CONCLUSION:
Acute nitrate ingestion led to significant decreases in the mean HR and RPE during high-intensity interval cycling, but no additional benefit was observed with higher nitrate content. These findings may assist practitioners in implementing more effective nitrate supplementation strategies to enhance performance and adaptation during interval exercise.