The Effect of Dietary Nitrate Supplementation on Maximal Cycling Power

Abstract

Muscle shortening velocity and power increase in the presence of nitric oxide (NO). NO bioavailability increases after consuming foods rich in dietary nitrate. There is a very high concentration of nitrate in concentrated beetroot juice. PURPOSE: The purpose of this study was to determine if beetroot juice can increase maximal cycling power compared to a nitrate-depleted beetroot juice placebo. METHODS: In this double-blind, crossover study, acute changes in maximal cycling power were determined after beetroot juice supplementation or consumption of a placebo. During each of four visits, seven trained athletes (n=5 cyclists, 2 alpine skiers) performed four bouts of maximal cycling (∼3s) using an inertial load cycle ergometer immediately before, then 2.5h after consuming a bolus (140ml) of either nitrate-rich (∼11.2mmol) beetroot juice or a nitrate-depleted placebo. A 2x2 Repeated Measures ANOVA was used to assess main effects of time (pre- vs. post-drink) and treatment (beetroot juice vs. placebo), and the interaction between time and treatment (α=0.05). RESULTS: There was a main effect for time (p=0.002), but not for treatment (p=0.14). There was a trend toward an interaction between time and treatment (p=0.11). Specifically, there was a greater increase in maximal power from pre- to post-beetroot juice supplementation (1071±321W vs 1134±339W) compared to the increase observed in the placebo trial (1117±315W vs. 1154±322W). CONCLUSIONS: The main effect for time was a somewhat unexpected finding. All pre-drink trials happened early in the morning (before 8:00 am), and the post-drink trials happened mid-morning (∼9:00-10:45 am). Therefore, our results may have been confounded by the circadian rhythm in core temperature and muscle power. Nevertheless, there was still a trend toward increased maximal power after beetroot juice supplementation in trained athletes compared to the observed increase after consuming the placebo. These findings warrant more research to determine if indeed dietary nitrate can increase maximal cycling power.