On the implication of dietary nitrate supplementation for the hemodynamic and fatigue response to cycling exercise

This study investigated the impact of dietary nitrate supplementation on peripheral hemodynamics, the development of neuromuscular fatigue, and time to task failure during cycling exercise. Eleven recreationally active male participants (27 +/- 5 yr, over dot (V)(O2max): 42 +/- 2 mL/kg/min) performed two experimental trials following 3 days of either dietary nitrate-rich beetroot juice (4.1 mmol NO3-/day; DNS) or placebo (PLA) supplementation in a blinded, counterbalanced order. Exercise consisted of constant load cycling at 50, 75, and 100 W (4 min each) and, at similar to 80% of peak power output (218 +/- 12 W), to task-failure. All participants returned to repeat the shorter of the two trials performed to task failure, but with the opposite supplementation regime (iso-time comparison; ISO). Mean arterial pressure (MAP), leg blood flow (QL; Doppler ultrasound), leg vascular conductance (LVC), and pulmonary gas exchange were continuously assessed during exercise. Locomotor muscle fatigue was determined by the change in pre to postexercise quadriceps twitch-torque (Delta Q(tw)) and voluntary activation (DVA; electrical femoral nerve stimulation). Following DNS, plasma [nitrite] (similar to 670 vs. -180 nmol) and [nitrate] (similar to 775 vs. -11 limol) were significantly elevated compared with PLA. Unlike PLA, DNS lowered both QL and MAP by similar to 8% (P < 0.05), but did not alter LVC (P = 0.31). VO2 across work rates, as well as cycling time to task-failure (similar to 7 min) and locomotor muscle fatigue following the ISO-time comparison were not different between the two conditions (Delta Qtw -42%, Delta VA -4%). Thus, despite significant hemodynamic changes, DNS did not alter the development of locomotor muscle fatigue and, ultimately, cycling time to task failure. NEW & NOTEWORTHY This study sought to characterize the impact of dietary nitrate supplementation on the hemodynamic response, locomotor muscle fatigue, and time to task failure during cycling exercise. Although nitrate supplementation lowered mean arterial pressure and exercising leg blood flow, leg vascular conductance and oxygen utilization were unaffected. Despite significant hemodynamic changes, there was no effect of dietary nitrate on neuromuscular fatigue development and, ultimately, cycling time to task failure.