Dietary Nitrate Supplementation Reduces The Oxygen Cost Of Submaximal Arm Crank Exercise

Abstract

There is evidence to suggest that the ingestion of > 5 mmol inorganic nitrate (NO3) can enhance exercise economy [lower pulmonary oxygen uptake [VO2]] and performance during cycling and running exercise. However, the effect of dietary NO3- supplementation on economy and performance during isolated upper-body exercise is less clear. PURPOSE: To test the hypothesis that dietary NO3- supplementation would improve economy and performance during arm cranking exercise. METHODS: Eight recreationally-active males were assigned in a randomized, double-blind, crossover design to receive NO3--rich beetroot juice (BR; 12.2 mmol NO3-·day-1) and NO3--depleted beetroot juice (PL; 0.01 mmol NO3-·day-1) for 7 days. On days 5 and 7 of supplementation, subjects completed two bouts of moderate-intensity exercise and one bout of severe-intensity exercise that was continued until exhaustion on an arm-crank ergometer. Resting venous blood samples were obtained, for later determination of plasma nitrite concentration ([NO2-]) and breath-by-breath VO2 were measured during all exercise tests. RESULTS: Plasma [NO2-] was higher following BR, compared to PL (PL: 86 ± 51 nM vs. BR: 542 ± 285 nM; P < 0.05). BR supplementation lowered steady-state VO2 during moderate-intensity exercise by 3% (PL: 0.93 ± 0.24 L·min-1 vs. BR: 0.90 ± 0.23 L·min-1; P < 0.05). Exercise economy and time-to-exhaustion (PL: 459 ± 102 vs. BR: 474 ± 135 s; P > 0.05) were not impacted by BR supplementation during severe-intensity arm cranking. CONCLUSIONS: Short-term dietary NO3- supplementation improved moderate-intensity exercise economy, but not severe-intensity exercise economy or tolerance, during arm-cranking exercise in recreationally-active subjects.