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

Abstract

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 years, VO₂max: 42±2ml/kg/min) performed two experimental trials following 3 days of either dietary nitrate-rich beetroot juice (4.1mmol 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 ~80% of peak power output (218±12W), 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). Mean arterial pressure (MAP), leg blood flow (Q_L; 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 post-exercise quadriceps twitch-torque (∆Q_tw) and voluntary activation (∆VA; electrical femoral nerve stimulation). Following DNS, plasma [nitrate] (~670 vs ~180 nmol) and [nitrite] (~775 vs ~11 nmol) were significantly elevated compared to PLA. Unlike PLA, DNS lowered both Q_L and MAP by ~8% (P2 across work rates, as well as cycling time to task-failure (~7min) and locomotor muscle fatigue following the ISO-time comparison were not different between the two conditions (∆Q_tw ~42%, ∆VA ~4%). Thus, despite significant hemodynamic changes, DNS did not alter the development of locomotor muscle fatigue and, ultimately, cycling time to task failure.