NITRATE SUPPLEMENTATION DOES NOT EXTEND ENDURANCE PERFORMANCE
Wilkerson, D. P., Hayward, G., Stephen, B. J., Vanhatalo, A., Blackwell, J. R., & Jones, A. M. (2012). Acute dietary nitrate supplementation does not improve 50-mile time-trial performance in highly trained cyclists. Presentation 1824 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.
This study determined the effect of acute dietary nitrate supplementation on 50-mile time-trial performance in trained cyclists (N = 8). After familiarization, Ss performed 50-mile time-trials under two experimental conditions: i) 2.5 hours after consuming 0.5 liters of beetroot juice containing ~6.2 mmol of nitrate; and ii) 2.5 hours after consuming 0.5 liters of nitrate-depleted beetroot juice containing ~0.005 mmol of nitrate (placebo). The two conditions were administered using a counter-balanced, single-blind, crossover design. A minimum of seven days separated visits to allow recovery and washout.
Beetroot juice significantly elevated plasma [nitrite] and resulted in a group mean reduction in completion time for the 50-mile time-trial of 0.8% which was not statistically different to the placebo condition. There was a significant correlation between the increased post-beverage plasma [nitrite] with beetroot juice and the reduction in time-trial completion times (r = -0.84). Power output was not different between the conditions at any point but oxygen uptake (VO2) tended to be lower in beetroot juice condition (non-significant), resulting in a significantly greater power output to oxygen uptake ratio.
Implication. Acute dietary nitrate supplementation with nitrate-rich beetroot juice did not significantly improve 50-mile time-trial performance in trained cyclists despite a significantly greater power output to oxygen uptake ratio. It appears that rather than attain a higher power output for a given oxygen uptake, the cyclists maintained a similar power output but at a lower oxygen uptake. Although the reduction in 50-mile time-trial completion time of 0.8% did not attain statistical significance, an improvement in performance of that magnitude would likely be meaningful to an athlete in a practical sense. The lack of statistical significance could be due to the weak power of the statistical analysis occasioned by the small number of Ss.
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