Antioxidant-rich beetroot juice does not adversely affect acute neuromuscular adaptation following eccentric exercise

This study examined the effects of beetroot juice on the repeated bout effect (RBE) to eccentric exercise. Twenty-nine recreationally active males performed two bouts of 100-drop jumps, separated by 14-21 days. Using a double-blind, independent groups design, participants consumed either a higher dose beetroot juice (H-BT; 250ml, n=10), a lower dose beetroot juice (L-BT; 125ml, n=9) or an isocaloric placebo (PLA; 250ml, n=10) for 3 days after bout 1; no drinks were consumed after bout 2. Maximal isometric voluntary contraction (MIVC), countermovement jump (CMJ), pressure-pain threshold (PPT) and creatine kinase (CK) were measured pre, post, 24, 48 and 72h following both bouts. In bout 2, CMJ and MIVC recovered quicker and CK activity was attenuated (versus bout 1) (P<0.05) in all groups, demonstrating an RBE. At 24h post bout 1, MIVC was 84.1 +/- 16.1, 83.6 +/- 11.6, 79.7 +/- 15.1% relative to baseline values in the H-BT, L-BT and PLA groups, respectively; at 24h post bout 2, MIVC recovered in the H-BT, L-BT and PLA groups, respectively. These findings suggest that supplementation with antioxidant-rich beetroot juice does not adversely affect acute adaptations to a bout of eccentric exercise.