Sodium phosphate loading has been reported to increase maximal oxygen uptake (6-12%), however its influence on endurance performance has been ambiguous. The aim of this study was to examine the influence of sodium phosphate loading on laboratory 16.1 km cycling time-trial performance. Six trained male cyclists (VO2 peak, 64.1 ± 2.8 ml kg-1 min-1; mean ± S.D.) took part in a randomised double-blind crossover study. Upon completion of a control trial (C), participants ingested either 1 g of tribasic dodecahydrate sodium phosphate (SP) or lactose placebo (P) four times daily for 6 days prior to performing a 16.1 km (10 mile) cycling time-trial under laboratory conditions. Power output and heart rate were continually recorded throughout each test, and at two points during each time-trial expired air samples and capillary blood samples were taken. There was a 14-day period between each of the supplemented time-trials. After SP loading mean power was greater than for P and C (C, 322 ± 15 W; P, 317 ± 16 W; SP, 347 ± 19 W; ANOVA, P < 0.05) and time to complete the 16.1 km was shorter than P, but not C (ANOVA, P < 0.05). During the SP trial, relative to the P, mean changes were mean power output +9.8 ± 8.0% (±95% confidence interval); time -3.0 ± 2.9%. There was a tendency towards higher VO2 after SP loading (ANOVA, P = 0.07). Heart rate, VE, RER and blood lactate concentration were not significantly affected by SP loading. Sodium phosphate loading significantly improved mean power output and 16.1 km time-trial performance of trained cyclists under laboratory conditions with functional increases in oxygen uptake.
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