The Effect of Nitrate Supplementation on Cycling Performance in the Heat in Well-Trained Cyclists

Abstract

Purpose: The aim of this study was to determine the effect of NO₃⁻ consumption on measures of perception, thermoregulation and cycling performance in hot conditions.

Methods: Using a randomised, double-blind, crossover-design, 8 well-trained cyclists (mean ± SD: age: 25 ± 8 y, V̇O2peak: 64 ± 5 ml·kg⁻¹·min⁻¹) performed 2 separate trials, in hot (35°C, 60% relative humidity) environments, having ingested either 140 ml NO3--rich beetroot juice ~8 mmol NO₃⁻ (NIT), or placebo (PLA), daily for 3-days with a 7-day washout period separating trials. Trials consisted of 2 × 10 min bouts at 40 and 60% peak power output (PPO) to determine physiological and perceptual responses in the heat, followed by a 4 km cycling time-trial.

Results: Basal [nitrite] was substantially elevated in NIT (2.70 ± 0.98 μM) vs PLA (1.10 ± 0.61 μM) resulting in a most likely (ES = 1.58 ± 0.93) increase after 3-days. There was a very likely trivial increase in rectal temperature [Tᵣₑ] in NIT at 40% (PLA;37.4 ± 0.2°C vs NIT;37.5 ± 0.3°C, 0.1 ± 0.2°C) and 60% (PLA;37.8 ± 0.2°C vs NIT;37.9 ± 0.3°C, 0.1 ± 0.2°C) PPO. Cycling performance was similar between trials (PLA;336 ± 45 W vs NIT;337 ± 50 W, CV±95%CL; 0.2 ± 2.5%). Outcomes for heart rate, and perceptual measures were unclear across the majority of time-points.

Conclusions: Three days of NO₃⁻ supplementation, resulted in small increases in Tᵣₑ during low- to moderate-intensity exercise, however this did not appear to influence 4 km cycling time-trial performance in hot climates.