The Effect of Inorganic Nitrate Supplementation on Muscle Fatigue in Healthy Adults; A Meta-Analysis

The Effect of Inorganic Nitrate Supplementation on Muscle Fatigue in Healthy Adults; A Meta-Analysis

Abstract: The positive effects of dietary supplementation with beetroot juice have been reported on diverse aspects of sports performance, but its impact on muscle fatigue remains unclear. Purpose: The purpose of this meta-analysis is to investigate the effect of beetroot juice supplement on muscle fatigue assessed by changes in strength or power outputs. Methods: Through the comprehensive search using major databases, 215 relevant studies were identified. Three search terms were used to identify potentially relevant articles; “Beetroot” AND “Exercise” AND “Fatigue.” Several moderator analyses were conducted to examine the effect of dosage, timing of supplementation, type of measure, gender, and participation on the overall effect size. Results: The results showed a significant positive effect of beetroot juice supplementation on muscle fatigue: the overall strength of ESs (Hedges’ g) was .334 (95% CI = .149, .520, p < .001; moderate effects; cf., Cohen’s criteria). The prediction interval was -.925 to 1.593, indicating that there are some populations for which the impact of beetroot juice on fatigue would be negative. There was no significant effect of moderators (participation (athletes vs. non-athletes), duration of supplement consumption, NO3 − concentration, gender, and type of measurement (power vs. strength) on the size of the effect. Conclusion: This study shows that dietary beetroot juice supplementation significantly reduces fatigue indicated by a decline in strength and power outputs.