Impact Of Dietary Nitrate Loading On Muscle Oxygenation During A Fatiguing Barbell Bench Press Protocol

Dietary nitrates have become a popular dietary supplement to improve overall health and exercise performance, in part, due to their proposed ability to improve blood flow to active musculature. However, current data regarding increased muscle blood flow following dietary nitrate consumption have been equivocal. PURPOSE: To assess the impact of 6 days of dietary nitrate loading, in the form of red spinach extract (RSE), on muscle oxygenation during a fatiguing barbell bench press protocol. METHODS: Ten resistance-trained males (22.7 ± 3.2 yrs, 80.5 ± 3 .9 kg, 1.79 ± 7.4 m, 7.4 ± 3.2 yrs of training experience) participated in this randomized, cross-over, placebo-controlled, double-blind investigation. Each participant completed 6 days of either RSE (2 g) or a maltodextrin placebo (PL) before reporting to the lab for testing in a counterbalanced fashion with a 14-day washout period between treatments. Upon reporting to the lab, participants were provided their last dose of RSE or PL 40 minutes before beginning a standardized warm-up and then completing 5 sets of the barbell bench press exercise at 75% of a predetermined 1-repetition maximum with 2-minute rest intervals. Participants were instructed to complete as many repetitions as possible until muscular failure. Percentage of oxygen saturation loss (∆%SmO2) during each bench press set, reoxygenation slope of the first 30 seconds of recovery following each set (SmO2slope), and total reoxygenation time (SmO2recT) in recovery following each set were assessed using a near-infrared spectroscopy device (NIRS). Data were analyzed via separate repeated measures analyses of variance. RESULTS: There were no significant time by group interactions for ∆%SmO2 (p = 0.143), SmO2recT (p = 0.368), or SmO2slope (p = 0.719) indicating similar responses between treatments. A trend for a main effect for time was observed for SmO2slope (p = 0.055; η2 = 0.137) with the recovery slope declining over the 4 rest periods between bench press sets. No other main effects for time were observed (p > 0.05). CONCLUSION: It appears that 6 days of dietary nitrate loading did not alter NIRS derived muscle oxygenation measures of the anterior deltoid during the bench press exercise in resistance-trained males.