Effect of Dietary Nitrate Intake on Fatigue Resistance Following Ischemia-Induced Microvascular Dysfunction in Males and Females.

BACKGROUND

Skeletal muscle fatigue reflects the interaction of metabolic demand, contractile efficiency, and oxygen delivery, processes highly dependent on microvascular function. Prolonged ischemia induces transient microvascular dysfunction that can impair fatigue resistance. Dietary nitrate, abundant in beetroot juice, enhances nitric oxide bioavailability and vascular function, but whether it mitigates ischemia-induced decrements in microvascular reactivity and fatigue resistance remains unclear.

OBJECTIVES

To determine whether a single oral dose of nitrate-rich beetroot juice (NR-BJ) protects against prolonged ischemia-induced impairments in microvascular function and fatigue resistance in a sex-dependent manner.

METHODS

Sixteen healthy adults (8 males, 8 females; 20-40 y) completed a randomized, double-blind, crossover trial with NR-BJ (∼10 mmol nitrate) or nitrate-depleted beetroot juice (ND-BJ, ∼0.34 mmol nitrate). Two hours postingestion, participants underwent 20 min of forearm arterial occlusion to induce microvascular dysfunction. Microvascular reactivity was assessed by near-infrared spectroscopy (tissue oxygen saturation resaturation slope), and fatigue resistance was determined during 50 maximal isokinetic wrist flexion-extension contractions. Serum nitrate and nitrite were measured by high-performance liquid chromatography.

RESULTS

Circulating nitrate and nitrite increased significantly after NR-BJ in both males and females. Prolonged ischemia reduced the tissue oxygen saturation resaturation slope in both sexes under the ND-BJ condition. NR-BJ attenuated this decline in females but not in males. In males, ischemia reduced total work and early-phase work (the first one-third of repetitions) under ND-BJ, effects that were prevented by NR-BJ. Fatigue resistance was preserved in females across conditions.

CONCLUSIONS

Acute dietary nitrate supplementation preserves fatigue resistance in males despite persistent microvascular dysfunction, whereas in females it attenuates ischemia-induced microvascular impairment without affecting fatigue resistance. These findings support sex-specific protective effects of dietary nitrate against transient vascular stress.