Effects of Dietary Nitrate Supplementation Over Four Weeks on Maximum Oxygen Consumption in Recreational Runners: A Pilot Study

Abstract

Introduction: Nutritional aids to improve exercise performance have become popular. One of the newest is dietary nitrate, often administered as a drink known as beetroot juice (BR). This has led many athletes, both elite and recreational, to consume BR prior to competition or physical activity. However, the results have been inconsistent and indicate that several factors need to be considered. Purpose: The purpose of this study was to evaluate the effects of BR consumption or placebo in two groups of recreational runners running a minimum of 15 miles per week. Methods: Ten women and three men volunteered to participate in this four week study. Each participant completed a maximal oxygen consumption test (VO 2max ). Data from the exercise test used for analysis included VO 2max , maximum heart rate (HR max ) and time of the maximal exercise test (T). Participants were then randomly assigned to either the Beetroot Juice Group (BRJ, n=7) or the Placebo Group (P, n=6). Each participant was given 16-four ounce bottles prefilled with the juice for their respective group. Participants were instructed to consume the juice 30 min prior to their exercise bouts (4/week) over the next four weeks, then return for follow-up testing. Results: Thirteen subjects completed the four week study (BRJ=7; P=6) and returned for posttesting. Statistical analyses were conducted using a two factor, repeated measures ANOVA to determine differences between the two groups for the initial and final VO 2max tests, as well as within the groups from pre-to post-testing after the four weeks. The initial values for VO 2max , (P=44.7±5.0 ml/kg/min; BRJ=47.6±8.4 ml/kg/min) HR max (P=174.7±15.6 bpm; BRJ=171.7±11.2 bpm), and T (P=12:06±1:26 min:sec; BRJ=12:22±0:08 min:sec) were not significantly different between the two groups (p>0.05). At the conclusion of the four week study, the results for the post maximal exercise test were VO 2max (P=45.0±6.3 ml/kg/ min; BRJ=49.3±8.8 ml/kg/min), HR max (P=171.7±16.6 bpm; BRJ=172.3±8.7 bpm), and T (P=12:06±1.36 min:sec; BRJ=12.43±0.07 min:sec) were not significantly different (p>0.05). However, there was a significant increase in the average time of the VO 2max test for the BRJ of 20.7 sec (p=0.02). None of the other variables measured over the four week training session were significantly different (p>0.05). Conclusion: These results indicate that dietary nitrate supplementation (16 oz/week) did not increase exercise performance with the exception of a significant increase in the average time of the VO 2max test for the BRJ group. This may be the result of learning to run on the treadmill or a reduction in the O 2 cost of exercise due to possible ergogenic effects of dietary nitrate supplementation. These findings may be further attributed to the varying training regimens, diets, and time of consumption.