Effects of phosphate loading on oxygen uptake, ventilatory anaerobic threshold, and run performance.

Seven male competitive runners (VO2max 73.9 +/- 6.3 ml.kg-1.min-1) participated in a two-session, placebo, double-blind study to determine the effects of phosphate loading on oxygen uptake, ventilatory anaerobic threshold, and 5-mile run performance. Subjects ingested 1000 mg of tribasic sodium phosphate or a placebo four times daily for 6 d. A maximal running stress test or a 5-mile performance run was performed randomly on either the 3rd or the 6th d. Test sessions were separated by a 2-wk washout period and repeated with alternating phosphate and placebo regimens. Venous blood samples were collected prior to and following each max and run session. Results revealed that placebo resting serum phosphate levels were mildly elevated and that phosphate loading significantly increased resting and post-exercise serum phosphate values. Resting and post-exercise 2,3-diphosphoglycerate values were decreased while hemoglobin values were elevated with phosphate ingestion. Phosphate loading significantly increased maximal oxygen uptake from 4.77 +/- 0.29 to 5.18 +/- 0.25 l.min-1 and ventilatory anaerobic threshold from 3.74 +/- 0.28 to 4.18 +/- 0.14 l.min-1. Five-mile run times were nonsignificantly different between placebo and phosphate sessions. However, mean performance run oxygen uptake was significantly lower (3.87 +/- 0.3 to 3.80 +/- 0.3 l.min-1) with phosphate ingestion. Data demonstrate that maximal and run performance were influenced by elevations in serum phosphate eliciting an increased maximal oxygen uptake, ventilatory anaerobic threshold, and variable effects on 5-mile run performance. These adaptations occurred without observable increases in red cell 2,3-diphosphoglycerate.