Article Title



Austin C. Hogwood1, Joaquin Ortiz de Zevallos Muñoz1, Ka'eo Kruse1, Jeison DeGuzman1, Meredith Buckley1, Arthur Weltman, FACSM1,2, Jason Allen, FACSM1,2. 1University of Virginia, Charlottesville, VA. 2University of Virginia School of Medicine, Charlottesville, VA.

Background: Inorganic nitrate (NO3-) supplementation increases nitric oxide (NO) bioavailability and may improve exercise performance. In females, estrogen increases endogenous eNOS production of NO, but estrogen fluctuates throughout the menstrual cycle (MC). It is unknown if different phases of the MC or exogenous NO3-supplementation impact maximal voluntary isometric contraction (MVIC), isokinetic torque, or power in apparently healthy young females. The purpose of this study was to examine potential differences in MVIC, isokinetic torque, and power between the early (EF) and late follicular (LF) phase of the MC, and with either beetroot juice (BR-containing ~13 mmol NO3-) or identical placebo (PL) supplementation. Methods: Seven recreationally active females (age: 24.7 ± 4 yrs, VO2peak: 34.4 ± 8 mL/kg/min) with normal MC and not using contraceptives were recruited in this double-blinded crossover study. Subjects were randomized to consume BR or PL, twice daily, for 5 days prior to testing that was conducted during EF and again during LF (1-5 and 11-14 days after menses onset, respectively). Subjects also consumed the supplement 2 hours prior to the testing, and a 14-day washout period was utilized between treatments. A linear mixed effects model was used to examine differences between MC phase, supplements, and interaction effects. MVIC (at 90°), peak torque (PT), PT normalized to bodyweight, time to PT, average PT, and average power were acquired via a Biodex isokinetic dynamometer during knee extension when measured at 180°, 270°, and 360°/second. Data are mean ± SD and significance was determined a priori at p < 0.05.Results: Mixed effects models revealed no significant differences in MVIC, power, or any measures of torque either between the MC, or the PL and BR supplementations (all p > 0.05). There were also no significant interaction effects for MVIC (PL EF: 1.12 ± 0.3; PL LF: 1.10 ± 0.3; BR EF: 1.18 ± 0.3; BR LF: 1.14 ± 0.3 Hz; p = 0.93) or any other outcomes. Conclusion: This preliminary data suggests that neither the follicular phase of the menstrual cycle, nor NO3- supplementation, impacts MVIC or outcomes such as peak torque or average power during isokinetic knee extension in healthy young females.

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