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

ABSTRACT

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 ± 4.4 years, VO_2peak 65.8 ± 5.5 mL.kg⁻¹.min⁻¹) completed four cycling TTs (14 kJ.kg⁻¹) in hot (35°C, 48% relative humidity) and euthermic (21°C, 52%) conditions, following 3 days supplementation with BR (6.5 mmol NO₃⁻ for 2 days and 13 mmol NO₃⁻ on the final day), or NO₃^–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.

KEYWORDS:

• Beetroot juice
• thermoregulation
• endurance

Acknowledgments

We would like to thank the participants for their time and effort in this study. The products from James White Drinks Ltd. were all purchased commercially.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Australian Institute of Sport under the High Performance Sport Research Fund.