The Effect Of Beetroot Juice Supplementation On Neuromuscular Performance: A Dose-response Investigation

1 Dietary nitrate (NO3-) supplementation can enhance type II muscle fiber function and thus explosive-type exercise. However, the ergogenic potential of NO3- during resistance exercise is scarce and it is unclear whether NO3- has a dose-dependent effect on resistance exercise performance. PURPOSE: To examine if acute NO3- ingestion elicits dose-dependent effects on nitric oxide bioavailability and resistance exercise performance in men. METHODS: Eighteen resistance-trained men were assigned in a double-blind, randomized, crossover design, to four conditions to consume beetroot juice containing: 1) 0 mmol NO3- (PL); 2) ~6 mmol NO3- (BR-LOW); 3) ~12 mmol NO3- (BR-MOD); and 4) ~24 mmol NO3- (BR-HIGH). Participants completed countermovement jumps, back squats, and bench press 2.5 h post-supplementation. A resting venous blood draw was obtained ~2.5 hours after supplementation. Nitric oxide bioavailability was measured via surrogate markers, plasma [NO3-] and [nitrite (NO2-)], using gas phase chemiluminescence. Neuromuscular performance outcomes were measured using a linear transducer and force plate. RESULTS: Plasma [NO3-] increased in a dose-dependent manner (P < 0.01) while plasma [nitrite] ([NO2-]) increased in 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). Neuromuscular performance was not different between conditions in countermovement jumps, 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. CONCLUSIONS: In young adult resistance-trained men, acute dietary NO3- does not appear to modulate resistance exercise performance. Lower NO3- doses may be required to increase the likelihood of ergogenic effects in back squats within this population. Supported by internal funding. Supported by: Internal funds from Pepperdine University.