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Joaquin Ortiz de Zevallos1, Austin C. Hogwood1, Ka’eo K. Kruse1, Jeison de Guzman1, Meredith Buckley1, Alexandra F. DeJong1,2, Arthur L. Weltman, FACSM1, Jason D. Allen, FACSM1. 1University of Virginia, Charlottesville, VA. 2The Micheli Center for Sports Injury Prevention, Boston, MA.

Nitric Oxide (NO) plays a pivotal role in muscle contractile function. Inorganic nitrate (NO3-) supplementation has been demonstrated to increase NO bioavailability and potentially improve exercise performance. Currently the effects of dietary nitrate (NO3-) on muscle function in young healthy females compared to males is understudied and unclear. Purpose: To determine sex-differences of dietary NO3- supplementation on skeletal muscle function during knee extension and muscular endurance during a time to failure (TF) task. Methods: Seven healthy females (age 24.0±3.6y, BMI 24.0±3.9) and ten healthy males (age 23.4±3.7y, BMI 25.1±2.6) were randomized in a double-blind, placebo-controlled crossover study. Female subjects were tested during the Early Follicular phase of the menstrual cycle to control for estrogen levels. Subjects ingested 70ml twice/day for 5 days, either NO3--rich Beet root juice (BRJ ~13mmol NO3-) or NO3--depleted placebo (PL). The last dose (140ml) was ingested 2h prior to laboratory arrival. Knee extension contractile function was assessed using a Biodex 4 isokinetic dynamometer at three different speeds (180°, 270°, and 360°/sec) during 10 consecutive maximal efforts. Subjects were given a thirty second rest between each speed. After a 5min rest, subjects completed a TF task which consisted of cycles of 3 sec contraction at 60% maximal isometric voluntary contraction and 2 sec rest for as long as possible. An inability to maintain the 60% threshold on three different occasions despite verbal encouragement throughout the test was considered as the end of the test. Results: Repeated Measures Two-Way ANOVA revealed that there were no significant differences in peak torque (nM/Kg), average power (watts/kg) and peak power (Watts/Kg) at all speeds for males or females between BR and PL conditions (p > 0.05 for all). Similarly, TF was not statistically different in females (PL; 269.14±161.17 vs BRJ; 277.14±157.50 sec; p > 0.05) or males (PL; 228.20±171.13 vs BRJ;194.13±99.65 sec; p > 0.05). Conclusion: Dietary nitrate supplementation did not increase muscle contractile function or endurance in healthy young males or females.

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