THE EFFECTS OF ACUTE DIETARY NITRATE SUPPLEMENTATION ON MAXIMAL EXERCISE PERFORMANCE

Abstract

INTRODUCTION: Beet juice has recently become a growing dietary supplement used by athletes to improve exercise performance. Beet juice is high in dietary nitrates which is absorbed in the upper gastrointestinal tract. The nitrate is then converted into nitrite which is further reduced to nitric oxide. Nitric oxide regulates muscle blood flow via vasodilation and mitochondrial respiration. Research shows that dietary nitrate supplementation reduces the oxygen cost of submaximal exercise for the same workload. This results in more mechanical efficiency of muscle contraction. PURPOSE: The purpose of this experiment was to determine if dietary nitrate improves aerobic exercise performance. METHODS: Three female and two male (age21±1yr) students from UTA, volunteered to participate in this study. Each subject had height and weight taken and body mass index (BMI) was calculated. The subjects were randomly assigned to either the placebo (PL) or beetroot juice (BR) group. Each subject performed a graded exercise test on the treadmill with increasing speed and elevation until exhaustion. On a separate day the subjects then returned to the lab and completed the test using the other drink. During each test heart rate (HRmax) and rate of perceived exertion (RPE) were recorded along with relative maximal oxygen consumption (VO2max) and time until exhaustion (T). RESULTS: The BMI for the subjects was 22.68±3.88. The maximal values:VO2max(PL:37.86±5.84ml/kg/min; BR:37.9±2.97ml/kg/min); RPE(PL:18±0.71;BR:18.6±0.89); and T(PL:10:41±.045min; BR:10:15±0.023L/min) were not significantly different between the groups (p>0.05). However, there was a statistically significant difference (p=0.035) between the groups for maximal heart rate (PL:196.8±10.08bpm; BR:193.6±11.19bpm). CONCLUSION: The results of this study indicate that acute beetroot juice supplementation does not have any effect on VO2max, RPE or T. However, HRmax is decreased during maximal exercise which can be attributed to increased mechanical efficiency of the cardiac muscle following supplementation.