Influence of acute dietary nitrate supplementation on oxygen delivery/consumption and critical impulse during maximal effort forearm exercise in males: a randomized crossover trial.

Abstract

Beetroot juice supplementation (BRJ) increases nitric oxide bioavailability under conditions of hypoxia and acidosis, characteristics of maximal effort exercise, which is required to identify forearm critical impulse. We hypothesized BRJ would improve oxygen delivery:demand matching and forearm critical impulse performance. Healthy males (20.8±2.4 years) participated in a randomized crossover trial between October 2017-May 2018 (Queen's University, Kingston, ON). Participants completed 10-minutes of rhythmic maximal effort forearm handgrip exercise 2.5 hours post placebo (PL) vs. BRJ (9 completed PL/BRJ vs. 4 completed BRJ/PL) within a 2 week period. Data are presented as mean±SD. There was a main effect of drink (PL > BRJ) for oxygen extraction (P=0.033,ηp2=0.351) and oxygen consumption/force (P=0.017,ηp2=0.417). There was a drink x time interaction (PL > BRJ) for oxygen consumption/force (P=0.035,ηp2=0.216) between 75-360s (1.25-6 min) from exercise onset. BRJ did not influence oxygen delivery (P=0.953,ηp2=0.000), oxygen consumption (P=0.064,ηp2=0.278), metabolites [[lactate] (P=0.196,ηp2=0.135), pH (P=0.759,ηp2=0.008)] or power-duration performance parameters [critical impulse (P=0.379,d=0.253), W' (P=0.733,d=0.097)]. BRJ during all-out handgrip exercise does not influence oxygen delivery or exercise performance. Oxygen cost of contraction with BRJ is reduced as contraction impulse is declining during maximal effort exercise resulting in less oxygen extraction. https://osf.io/pga37/registrations.