The Effect of Dietary Nitrate Supplementation on Physiology and Performance in Trained Cyclists

Abstract

Purpose: To determine the effect of dietary nitrate (NO₃^-) supplementation on physiology and performance in well-trained cyclists after 6-8 d of NO₃^- supplementation.

Methods: Eight competitive male cyclists (mean ± SD age 26 ± 8 y, body mass 76.7 ± 6.9 kg, VO_2peak 63 ± 4 mL · kg^-1 · min^-1) participated in a double-blind, placebo-controlled, crossover-design study in which participants ingested 70 mL of beetroot juice containing ~4 mmol NO₃^- (NIT) or a NO₃^--depleted placebo (PLA), each for 8 d. Replicating pretreatment measures, participants undertook an incremental ramp assessment to determine VO_2peak and first (VT₁) and second (VT₂) ventilatory thresholds on d 6 (NIT6 and PLA6), moderate-intensity cycling economy on d 7 (NIT7 and PLA7), and a 4-km time trial (TT) on d 8 (NIT8 and PLA8).

Results: Relative to PLA, 6 d of NIT supplementation produced unclear effects for VO_2peak (mean ± 95% confidence limit: 1.8% ± 5.5%) and VT₁ (3.7% ± 12.3%) and trivial effects for both VT₂ (-1.0% ± 3.0%) and exercise economy on d 7 (-1.0% ± 1.6%). However, effects for TT performance time (-0.7% ± 0.9%) and power (2.4% ± 2.5%) on d 8 were likely beneficial.

Conclusions: Despite mostly unclear outcomes for standard physiological determinants of performance, 8 d of NO₃^- supplementation resulted in likely beneficial improvements to 4-km TT performance in well-trained male endurance cyclists.

Keywords: beetroot juice; cycling; economy; time trial.