Dietary nitrate and O₂ consumption during exercise

Abstract

Recent studies have investigated the influence of dietary nitrate supplementation on the physiological responses to exercise. Specifically, it has been reported that enhancing nitric oxide (NO) bioavailability through supplementation of the diet with nitrate salts or nitrate-rich beetroot juice reduces the O(2) cost of exercise and improves exercise performance. The lower O(2) cost for a given sub-maximal work rate following nitrate ingestion indicates that muscle efficiency is enhanced either as a consequence of a reduced energy cost of contraction or enhanced mitochondrial efficiency. The positive effects of nitrate supplementation on the O(2) cost of sub-maximal exercise can be manifested acutely (i.e. 2.5 h following ingestion) and maintained for at least 15 days if supplementation is continued. Most recently, the influence of dietary nitrate supplementation on time trial performance in competitive cyclists has been investigated. Studies have shown a 1-2% reduction in the time to complete time trial distances between 4 and 16 km. The dose of nitrate that has been shown to improve exercise efficiency can readily be achieved through the consumption of 0.5 litre of beetroot juice or an equivalent high-nitrate foodstuff. Following a 5- to 6-mmol bolus of nitrate, plasma [nitrite] typically peaks within 2-3 h and remains elevated for a further 6-9 h before declining towards baseline. Therefore, consuming nitrate approximately 3 h prior to competition or training is recommended if athletes wish to explore the ergogenic potential of nitrate supplementation.