Dietary nitrate supplementation does not improve cycling time-trial performance in the heat.

This investigation examined the effect of beetroot juice (BR) supplementation, a source of dietary nitrate (NO), on cycling time-trial (TT) performance and thermoregulation in the heat. In a double-blind, repeated-measures design, 12 male cyclists (age 26.6 ± 4.4 years, VO 65.8 ± 5.5 mL.kg.min) completed four cycling TTs (14 kJ.kg) in hot (35°C, 48% relative humidity) and euthermic (21°C, 52%) conditions, following 3 days supplementation with BR (6.5 mmol NO for 2 days and 13 mmol NO on the final day), or NOdepleted placebo (PLA). Salivary NO and nitrite, core (T) and mean skin temperature (T) were measured. Salivary NO and nitrite increased significantly post-BR supplementation (p < 0.001). Average TT completion time (mm:ss) in hot conditions was 56:50 ± 05:08 with BR, compared with 58:30 ± 04:48 with PLA (p = 0.178). In euthermic conditions, average completion time was 53:09 ± 04:35 with BR, compared with 54:01 ± 04:05 with PLA (p = 0.380). The TT performance decreased (p < 0.001), and T (p < 0.001) and T (p < 0.001) were higher in hot compared with euthermic conditions. In summary, BR supplementation has no significant effect on cycling TT performance in the heat.