THE EFFECT OF ACUTE BEETROOT JUICE SUPPLEMENTATION ON MUSCULAR STRENGTH AND ENDURANCE

Abstract

Dietary nitrate (NO3 -) supplementation with beetroot juice (BRJ) has previously been shown to reduce the oxygen cost of submaximal exercise and prolong the onset of fatigue. Nitric-oxide stimulating supplements such as l-Arginine have been found to increase muscular strength and endurance during resistance exercise. However, the effect of NO3 - supplementation via BRJ on muscular strength and endurance is currently unknown. Therefore the aim of this study was to investigate the effects of acute BRJ supplementation on muscular strength and endurance during resistance exercise. Ten physically active males (20 ± 1yrs, 180 ± 5cm, 84 ± 11kg) volunteered to participate within the study. Following an initial measure of one repetition max (1RM) leg press participants were randomly assigned to consume either 70ml BRJ (NO3 -: 4.0mmol) or 70ml placebo (PLA) (containing negligible NO3 -) in a blind, crossover design. Participants were required to consume the assigned supplement 2.5 hours prior to the performance of both 1RM leg press and 60% 1RM to muscular failure (TLV). Leg press 1RM significantly increased following BRJ, compared to PLA (BRJ =435 ± 52 vs. PLA = 423 ± 49kg). No significant difference was observed in leg press TLV between BRJ and PLA (P=0.06). Additionally, there was no effect of BRJ on heart rate, systolic and diastolic blood pressure at rest or post-exercise. These results indicate that acute BRJ supplementation improves muscular strength, but not muscular endurance. However increased doses of NO3 - and repeated bouts of resistance exercise may be required to elicit further ergogenic effect of BRJ supplementation.