Dietary nitrate does not acutely enhance skeletal muscle blood flow and vasodilation in the lower limbs of older adults during single-limb exercise.

Purpose: Blood flow (BF) and vasodilator responses to knee-extension exercise are attenuated in older adults across an exercise transient (onset, kinetics, and steady-state), and reduced nitric oxide bioavailability (NO) has been hypothesized to be a primary mechanism contributing to this attenuation. We tested the hypothesis acute dietary nitrate (NO) supplementation (~ 4.03 mmol NO and 0.29 mmol NO) would improve leg vasodilator responses across an exercise transient during lower limb exercise in older adults.

Methods: Older (n = 10) untrained adults performed single and rhythmic knee-extension contractions at 20% and 40% work-rate maximum (WR) prior to and 2-h after consuming a NO or placebo beverage in a double-blind, randomized fashion. Femoral artery BF was measured by Doppler ultrasound. Vascular conductance was calculated using BF and mean arterial pressure.

Results: Acute ingestion of dietary NO enhanced plasma [NO] and [NO] (P < 0.05). Neither dietary NO or placebo enhanced vasodilator responses at the onset of exercise or during steady state at 20% and 40% WR (P > 0.05). Leg vasodilator kinetics during rhythmic exercise remained unchanged following NO and placebo ingestion (P > 0.05).

Conclusions: The key findings of this study are that despite increasing plasma [NO] and [NO] acute dietary NO intake had no effect on (1) rapid hyperaemic or vasodilator responses at the onset of exercise; (2) hyperaemic and vasodilator responses during steady-state submaximal exercise; or (3) kinetics of vasodilation preceding steady-state responses. Collectively, these findings suggest that low dose dietary NO supplementation does not improve hyperaemic and vasodilator responses across an exercise transient in older adults.