The Effects of Sodium Phosphate Supplementation on Physiological Responses to Submaximal Exercise and 20 km Cycling Time-Trial Performance

The aim of this study was to examine the effects of sodium phosphate (SP) supplementation on 26 physiological responses to submaximal exercise and 20 km cycling time-trial performance. Using a 27 randomised, double-blind, crossover design, 20 endurance-trained male cyclists (age: 31 ± 6 years; 28 height: 1.82 ± 0.07 m; body mass: 76.3 ± 7.0 kg; maximal oxygen uptake [V̇O2max]: 57.9 ± 5.5 mL·kg-29 1·min-1) completed two supplementation trials separated by a 14-day washout period. The trials 30 consisted of 10 minutes of cycling at 65% V̇O2max followed by a 20 km time-trial. Expired air was 31 monitored throughout each trial for the evaluation of V̇O2, minute ventilation (V̇E), and respiratory 32 exchange ratio (RER). Heart rate was monitored during each trial along with ratings of perceived 33 exertion (RPE) and blood lactate concentration. For four days before each trial, participants ingested 50 34 mg∙kg fat-free-mass-1·day-1 of either SP or placebo. There were no effects (p ≥ 0.05) of supplementation 35 on physiological responses during cycling at 65% V̇O2max. There were also no effects of 36 supplementation on time-trial performance (placebo: 32.8 ± 2.2 mins; SP: 32.8 ± 2.3 mins). 37 Nevertheless, relative to placebo, SP increased V̇E (mean difference: 3.81 L·min-1; 95% likely range: 38 0.16-7.46 L·min-1), RER (mean difference: 0.020; 95% likely range: 0.004-0.036), and RPE (mean 39 difference: 0.39; 95% likely range: 0.04-0.73) during time-trials; as well as post time-trial blood lactate 40 concentration (mean difference: 1.06 mmol·L-1; 95% likely range: 0.31-1.80 mmol·L-1). In conclusion, 41 SP supplementation has no significant effects on submaximal physiological responses or 20 km time-42 trial performance.