Beetroot Juice Does Not Enhance Supramaximal Intermittent Exercise Performance in Elite Endurance Athletes

摘要

Objective: Nitrate (NO3-)-rich beetroot juice (BR) is recognized as an ergogenic supplement that improves exercise tolerance during submaximal to maximal intensity exercise in recreational and competitive athletes. A recent study has investigated the effectiveness of BR on exercise performance during supramaximal intensity intermittent exercise (SIE) in Olympic-level track cyclists, but studies conducted in elite endurance athletes are scarce. The present study aimed to determine whether BR supplementation enhances the tolerance to SIE in elite endurance athletes. Methods: Eleven elite endurance athletes (age: 21.7 +/- 3.7 years, maximal oxygen uptake 71.1 +/- 5.2 mL center dot kg(-1)center dot min(-1)) performed an SIE test until exhaustion following either a 3-day BR supplementation (340 mg/d) or a placebo (PL) supplementation (<2.5 mg/d) in a randomized, single blind, placebo-controlled, and crossover study. The exercise test consisted of 15-second cycling exercise bouts at 170% of the maximal aerobic power interspersed with 30-second passive recovery periods. Gas exchange was measured during SIE tests as local muscle O-2 delivery and extraction were assessed by near infrared spectroscopy. Results: The number of repetitions completed was not significantly different between BR (13.9 +/- 4.0 reps) and PL conditions (14.2 +/- 4.5 reps). BR supplementation did not affect oxygen uptake () during SIE tests (BR: 3378.5 +/- 681.8 mL center dot min(-1), PL: 3466.1 +/- 505.3 mL center dot min(-1)). No significant change in the areas under curves was found for local muscle total hemoglobin (BR: 6816.9 +/- 1463.1 arbitrary units (a.u.), PL: 6771.5 +/- 3004.5 a.u.) and deoxygenated hemoglobin (BR: 6619.7 +/- 875.8 a.u., PL: 6332.7 +/- 1336.8 a.u.) during time-matched work + recovery periods from SIE tests following BR supplementation. Conclusions: BR supplementation does not enhance the tolerance to SIE in elite endurance athletes and affects neither nor local muscle O-2 delivery and extraction.