The effect of dietary nitrate supplementation on resistance exercise performance: A dose-response investigation.

Abstract

Dietary nitrate (NO₃^-) can enhance skeletal muscle contractile function and explosive-type exercise by modulating type II muscle fibers; however, limited attention has been directed at exploring the optimal dosing guidelines and potential performance-enhancing effects of NO₃^- supplementation during resistance-type exercise. The purpose of our investigation was to examine potential dose-response effects of concentrated NO₃^--rich beetroot juice on neuromuscular performance during resistance exercise. Eighteen resistance-trained men were assigned in a double-blind, randomized, crossover design, to four conditions to consume beetroot juice containing: negligible NO₃^- (PL); ~ 6 mmol NO₃^- (BR-LOW); ~ 12 mmol NO₃^- (BR-MOD); and ~ 24 mmol NO₃^- (BR-HIGH). Participants completed 1 set of vertical countermovement jumps (CMJ), 2 sets × 3 repetitions of barbell back squats, and 2 sets × 3 repetitions of barbell bench press 2.5 h post-supplementation. Plasma [NO₃^-] increased in a dose-dependent manner (P < 0.01). Plasma [nitrite] ([NO₂^-]) increased in all BR conditions compared to PL (P < 0.05), such that BR-MOD vs. BR-LOW (P < 0.01) and BR-LOW vs. PL (P < 0.01), but BR-HIGH was not different compared to BR-MOD (P > 0.05). Performance was not different between conditions in CMJ, 50% one-repetition maximum (1RM) and 75%1RM back squats, or 50%1RM and 75%1RM bench press (P > 0.05). The change in plasma [NO₂^-] was significantly correlated with peak power (r = - 0.65, P = 0.003), mean power (r = - 0.52, P = 0.03), and mean velocity (r = - 0.48, P = 0.04) during 50%1RM back squats following BR-LOW vs. PL but not in other conditions (P > 0.05). This study indicates that dietary NO₃^- does not impact resistance exercise performance at any of the doses assessed in the current study.