Effects of sodium phosphate and beetroot juice supplementation on repeated-sprint ability in females

Introduction Sodium phosphate (SP) and beetroot juice (BJ) supplementation was assessed on repeated-sprint ability (RSA). Methods Thirteen female team-sport participants completed four trials: (1) SP and BJ (SP + BJ), (2) SP and placebo (for BJ), (3) BJ and placebo (for SP) and (4) placebo (for SP + BJ), with ~21 days separating each trial. After each trial, participants performed a simulated team-game circuit (STGC) consisting of four 15 min quarters, with a 6 × 20-m repeated-sprint set performed at the start, half-time and end. Results Total sprint times were between 0.95–1.30 and 0.83–1.12 s faster for each RSA set and 3.25 and 3.12 s faster overall (~5 % improvement) after SP compared with placebo and BJ, respectively (p = 0.02 for sets 1, 2 and overall; Cohen’s effect size: d = −0.51 to −0.90 for all sets and overall). Additionally, total sprint times were 0.48 s faster after SP + BJ compared with placebo (set 2; p = 0.05, ~2 % improvement). Furthermore, best sprints were 0.13–0.23 and 0.15–0.20 s faster (~6 % improvement; p < 0.01) after SP compared with placebo and BJ, respectively, for all sets (d = −0.54 to −0.89). Conclusion SP improved RSA in team-sport, female athletes when fresh (set 1) and during the later sets of a STGC (sets 2 and 3). Specifically, total and best sprint times were faster after SP compared with placebo and BJ.