Background: Athletes continue to strive for an edge over the competition. In recent years, dietary nitrate supplementation, particularly in the form of beetroot juice, has been shown to improve oxygen cost economy in endurance-focused submaximal intensity exercise and extend the time to exhaustion during maximal intensity exercise. However, scarce literature exists on the effects of nitrate supplementation on sports that focus mainly on strength and power. CrossFit is a sport that relies on strength, power, and endurance, and incorporates high-intensity, Olympic-based lifting and interval training exercises. Purpose: To investigate the effects of six days of dietary nitrate supplementation on strength, power and endurance in CrossFit athletes. Methods: Twelve male CrossFit athletes (age, 23 ± 5 years; CrossFit training [greater than]3 days/week for at least 4 months) participated in this randomized, crossover, double-blind, placebo-controlled study. After familiarization, baseline testing for peak aerobic capacity (VO₂peak), anthropometrics, and body composition (BodPod®) was performed. A three-day food log was completed both before and after the completion of the study. The food consumed 24 hours before the first trial was followed for each subsequent trial. Day 1 baseline testing included a blood draw for plasma nitrate and nitrite, as well as strength (Biodex), power (Wingate), and endurance (2K row) tests. Day two consisted of a sport-specific CrossFit circuit known as Grace. After testing, participants consumed either 8 mmol potassium nitrate (N) or 8 mmol of potassium chloride (PL) in pill form for six days. After this period, the participants returned for post-testing, had a 10-day washout period, and then returned for baseline and post-testing consuming the opposite supplement. Repeated measures of analysis of variance and a Student's T-test (SPSS Version 21, Cary, NC) were used to compare results. Results: There were no significant differences in dietary intake except for fiber (PRE: 22 ± 9 vs POST: 27 ± 11 g, P = 0.03). Plasma nitrate did not significantly change in N (PRE: 146.77 ± 69.48 vs POST: 192.05 ± 69.48 nM, P = 0.07) but did significantly increase in PL (PRE: 140.96 ± 59.98 vs POST: 204.82 ± 64.82 nM, P = 0.02). There were no significant differences for isokinetic strength measurements, but for isometric extension 60° there was a main effect of time (P = 0.03) which equated to a 17.23 ± 13.04 Nm (10.19 ± 36.60 %) increase in force in N and a 10.65 ± 6.42 Nm (6.11 ± 17.36 %) increase in PL. The Wingate power test resulted in a main effect of time, but no group x time effect. However, N increased 58.92 ± 7.11 W (6.62 ± 3.96 %), but PL only increased 6.92 ± 26.01 W (0.77 ± 14.19 %; P = 0.08). No significant differences between groups were measured for the 2000-m rowing test. While not statistically significant, the time to complete the Grace circuit improved on average by -32.35 ± 53.24 sec (-8.94 ± 31.14 %) in N compared to a -10.83 ± 12.68 sec (-3.84 ± 8.94 %) in PL. Conclusion: Consuming dietary nitrate in the potassium nitrate salt form did not statistically improve strength, power, or endurance in male CrossFit athletes. However, while not statistically significant, the improvement in the time to complete the sport specific Grace test using N may be meaningful during competition.
