Oxygen delivery and cardiac output during exercise following oral phosphate-glucose

Phosphate has been proposed as an ergogenic aid since it may enhance O2 delivery and cardiac work efficiency by increasing plasma phosphate (P Pi), red blood cell phosphate (RBC Pi), 2,3-diphosphoglycerate (DPG), RBC adenosine triphosphate (ATP), and P50. In 10 normal, fasting males we measured cardiac output (Q) by CO2 rebreathing, heart rate (HR), O2 deficit (O2DEF), and O2 consumption (VO2) during cycle ergometer exercise (60% of peak VO2). Stroke volume (SV) and arteriovenous O2 difference (A-VO2) were calculated. Following a baseline blood sample (BASE) for P Pi, RBC Pi, DPG, RBC ATP, and P50 (3 h before exercise), a single oral dose of dicalcium phosphate (129 mmol) and glucose (500 ml/10% sol, PHOS), or placebo (PLA), was administered in a random, crossover, double-blind fashion. Blood sampling was repeated immediately before and after exercise (PRE-EX and POST-EX). PHOS induced increases in P Pi (3.87 to 4.35 mg.dl-1, P less than 0.05), RBC Pi (3.86 to 4.63 mg.dl-1, P = 0.08), DPG (11.8 to 13.1 mumol.g-1 Hb, P less than 0.05), RBC ATP (4.2 to 4.4 mumol.g-1 Hb, P less than 0.05), and P50 (26.8 to 27.9 mm Hg, P less than 0.05) from BASE to PRE-EX. All variables remained elevated through the exercise period, as evidenced by higher levels than BASE at POST-EX (P less than 0.05). However, P50 was not different across conditions at PRE-EX (PHOS P50 = 27.9, PLA P50 = 28.3 mm Hg) or POST-EX (PHOS P50 = 28.0, PLA P50 = 28.1 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)