The influence of sex on the effects of inorganic nitrate supplementation on muscular power and endurance

Inorganic nitrate ([Formula: see text]) supplementation increases nitric oxide (NO) bioavailability and may improve muscular power and endurance, although most studies are in males. Therefore, the present double-blind, randomized, placebo-controlled study examined the effects of [Formula: see text] supplementation on isokinetic peak power, maximal voluntary isometric contraction (MVIC) force, muscular endurance (time-to-task failure; TTF), and recovery from fatigue in young females (<i>n</i> = 12) and males (<i>n</i> = 14). Participants consumed ∼13 mmol [Formula: see text] [beetroot juice (BRJ)], or an identical [Formula: see text]-depleted beverage placebo (PL), for ∼3 days and 2 h before testing visits. Plasma nitrate and nitrite were elevated in the BRJ condition (<i>P</i> ≤ 0.05). Peak power (W·kg^-1) showed a sex effect (<i>P</i> ≤ 0.05) at all angular velocities and a sex-by-treatment effect at 270 and 360°/s (<i>P</i> ≤ 0.05). Post hoc analysis revealed no significant differences between treatments (<i>P</i> > 0.05). Estimated maximal knee extension power (<i>P</i>_max) and maximal knee extension velocity (<i>V</i>_max) demonstrated no sex, treatment, or sex-by-treatment effect (<i>P</i> > 0.05). There were no significant effects for TTF (F: PL; 269 ± 161 vs. BRJ; 277 ± 158 s and M: PL; 228 ± 171 vs. BRJ; 194 ± 100 s; <i>P</i> > 0.05). Cohen's <i>d</i> effect sizes for peak power showed moderate to large effect sizes at 270 (<i>d</i> = 0.92) and 360°/s (<i>d</i> = 0.81), showing a possible differentiated effect of dietary nitrate in females and males. The present data indicate that [Formula: see text] supplementation does not significantly affect knee extensor maximal power, maximal contraction velocity, and muscular endurance in either sex. The sex-dependent response to dietary nitrate supplementation requires further investigation as data on females is scarce.<b>NEW & NOTEWORTHY</b> Recent data have suggested that inorganic nitrate ([Formula: see text]) supplementation may benefit males; however, females may experience worsened endurance capacity. This study revealed a potential differentiated effect of [Formula: see text] supplementation on outcomes of muscle contractile function between healthy, young males and females. The specific responses of [Formula: see text] supplementation in females and across sexes remain understudied and require further investigation.