Effects of Sodium Phosphate Supplementation on Physiological Responses 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 and 20 km cycling time-trial performance. Using a randomised, counterbalanced, double-blind, crossover design, 20 moderately-trained male cyclists (age: 31 ± 6 years; height: 1.82 ± 0.07 m; body mass: 76.3 ± 7.0 kg; maximal oxygen uptake: 57.9 ± 5.5 mL·kg-1·min-1) completed two experimental trials separated by a 14 day washout period. The experimental trials consisted of 10 min of steady-state cycling (electromagnetically-braked ergometer) at 65% of the power output required to elicit maximal oxygen uptake followed by a 20 km time-trial (racing bicycle fitted to a turbo trainer). For four days before each experimental trial, participants ingested gelatine capsules containing 50 mg∙kg fat-free mass-1·day-1 of either SP or maltodextrin (placebo). There were no effects (p ≥ 0.05) of supplementation on physiological responses during steady-state cycling. There were also no effects (p ≥ 0.05) of supplementation on oxygen uptake or heart rate during time-trial performance. Relative to placebo, SP increased minute ventilation (mean difference: 3.81 L·min-1; 95% likely range: 0.16-7.46 L·min-1), respiratory exchange ratio (mean difference: 0.020; 95% likely range: 0.004-0.036), and rating of perceived exertion (mean difference: 0.39; 95% likely range: 0.04-0.73) during time-trial performance. Relative to placebo, SP also enhanced post-time-trial blood lactate concentration (mean difference: 1.06 mmol·L-1; 95% likely range: 0.31-1.80 mmol·L-1). However, there were no effects (p ≥ 0.05) of supplementation on time-trial completion time, power output, or cycling cadence. Although SP supplementation may enhance extracellular buffering during high-intensity exercise, the results of this study show that SP supplementation has no significant effects on submaximal physiological responses or time-trial performance.