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<h4>Purpose</h4>Nitrate (NO3-), through its conversion to nitrite (NO2-) and nitric oxide, has been shown to increase exercise tolerance in healthy younger adults and older diseased patients. Nitrate's effect in well-trained middle to older-aged adults has not been studied. Therefore, the purpose of this investigation was to examine the effects of a NO3- rich beverage on submaximal constant work rate exercise time in well-trained middle to older-aged adults.<h4>Methods</h4>This was a randomized controlled cross-over trial with 15 well-trained middle to older-aged adults, 41-64 year-old, who received one of two treatments (NO3- rich beverage then placebo or placebo then NO3- rich beverage), after which an exercise test at 75 percent of the subject's maximal work rate was completed.<h4>Results</h4>The NO3- rich beverage increased plasma NO3- and NO2- levels by 260 μM and 0.47 μM, respectively (p<0.001). Exercise time was not significantly different (p = 0.31) between the NO3- rich versus placebo conditions (1130±151 vs 1060±132 sec, respectively). Changes in exercise time between the two conditions ranged from a 55% improvement to a 40% decrease with the NO3- rich beverage. Oxygen consumption and rating of perceived exertion were not significantly different between the two conditions.<h4>Conclusion</h4>In middle to older-aged well-trained adults, NO3- supplementation has non-significant, albeit highly variable, effects on exercise tolerance. ClinicalTrials.gov Identifier: NCT03371966.