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 (NO3-), on cycling time-trial (TT) performance and thermoregulation in the heat. In a double-blind, repeated-measures design, 12 male cyclists (age 26.6 +/- 4.4years, VO2peak 65.8 +/- 5.5mL.kg(-1).min(-1)) completed four cycling TTs (14kJ.kg(-1)) in hot (35 degrees C, 48% relative humidity) and euthermic (21 degrees C, 52%) conditions, following 3days supplementation with BR (6.5mmol NO3- for 2days and 13mmol NO3- on the final day), or NO(3)(-)depleted placebo (PLA). Salivary NO3- and nitrite, core (T-c) and mean skin temperature (T-sk) were measured. Salivary NO3- 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-c (p<0.001) and T-sk (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.