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This study investigated the effects of a beet nitric oxide enhancing (NOE) supplement comprised of nitrite and nitrate on cycling performance indices in trained cyclists., Methods: Subjects completed a lactate threshold test and a high-intensity interval (HIIT) protocol at 50% above functional threshold power with or without oral NOE supplement., Results: NOE supplementation enhanced lactate threshold by 7.2% (Placebo = 191.6 ± 37.3 W, NOE = 205.3 ± 39.9; p = 0.01; Effect Size (ES) = 0.40). During the HIIT protocol, NOE supplementation improved time to exhaustion 18% (Placebo = 1251 ± 562s, NOE = 1474 ± 504s; p = 0.02; ES = 0.42) and total energy expended 22.3% (Placebo = 251 ± 48.6 kJ, NOE = 306.6 ± 55.2 kJ; p = 0.01; ES = 1.079). NOE supplementation increased the intervals completed (Placebo = 7.00 ± 2.5, NOE = 8.14 ± 2.4; p = 0.03; ES = 0.42) and distance cycled (Placebo = 10.9 ± 4.0 km, NOE = 13.5 ± 3.9 km; p = 0.01; ES = 0.65). Also, target power was achieved at a higher cadence during the HIIT work and rest periods (p = 0.02), which enhanced muscle oxygen saturation (SmO 2 ) recovery. Time-to-fatigue was negatively correlated with the degree of SmO 2 , desaturation during the HIIT work interval segment (r = -0.67; p 0.008), while both SmO 2 desaturation and the SmO 2 starting work segment saturation level correlated with a cyclist's kJ expended (SmO 2 desaturation: r = -0.51, p = 0.06; SmO 2 starting saturation: r = 0.59, p = 0.03)., Conclusion: NOE supplementation containing beet nitrite and nitrate enhanced submaximal (lactate threshold) and HIIT maximal effort work. The NOE supplementation resulted in a cyclist riding at higher cadence rates with lower absolute torque values at the same power during both the work and rest periods, which in-turn delayed over-all fatigue and improved total work output., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. There are no actual or potential conflicts of interest for the authors on this paper with the exception for Dr. John L. Ivy from the University of Texas at Austin. Dr. Ivy is currently President of the Scientific Advisory Board of HumanN. Dr Ivy helped design the study, interpret the results and write the manuscript. He was not involved in data collection of analysis., (© 2021 The Author(s).)