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 physiological responses to submaximal exercise and 20 km cycling time-trial performance. Using a randomized, double-blind, crossover design, 20 endurance-trained male cyclists (age: 31 ± 6 years; height: 1.82 ± 0.07 m; body mass: 76.3 ± 7.0 kg; maximal oxygen uptake [V̇O_2max]: 57.9 ± 5.5 mL·kg^-1·min^-1) completed two supplementation trials separated by a 14-day washout period. The trials consisted of 10 minutes of cycling at 65% V̇O_2max followed by a 20 km time trial. Expired air was monitored throughout each trial for the evaluation of V̇O₂, minute ventilation (V̇_E), and respiratory exchange ratio (RER). Heart rate was monitored during each trial along with ratings of perceived exertion (RPE) and blood lactate concentration. For four days before each trial, participants ingested 50 mg·kg fat-free mass^-1·day^-1 of either SP or placebo. There were no effects (p ≥ .05) of supplementation on physiological responses during cycling at 65% V̇O_2max. There were also no effects of supplementation on time-trial performance (placebo: 32.8 ± 2.2 min; SP: 32.8 ± 2.3 min). Nevertheless, relative to placebo, SP increased V̇_E (mean difference: 3.81 L·min^-1; 95% confidence interval: [0.16, 7.46 L·min^-1]), RER (mean difference: 0.020; 95% confidence interval: [0.004, 0.036]), and RPE (mean difference: 0.39; 95% confidence interval: [0.04, 0.73]) during time trials, as well as post time-trial blood lactate concentration (mean difference: 1.06 mmol·L^-1; 95% confidence interval: [0.31, 1.80 mmol·L^-1]). In conclusion, SP supplementation has no significant effects on submaximal physiological responses or 20 km time-trial performance.