Sports Fitness Training

Numerous mechanisms have been proposed by which phosphates increase endurance performance. Phosphates may increase extra- and intracellular levels of phosphate, thereby increasing the amount of phosphate available for oxidative phosphorylation and phosphocreatine synthesis. Phosphates are also thought to increase the production of 2,3-diphosphoglycerate (2,3-DPG) in red blood cells (RBCs). 2,3-DPG aids the release of oxygen from hemoglobin on RBCs. The increase in 2,3-DPG concentrations shifts the oxygen-hemoglobin curve to the right, allowing for more oxygen to be delivered to skeletal muscles.The final proposed mechanism of action for phosphates is the notion that phosphates are buffers, which supposedly decreases the accumulation of hydrogen ions that can inhibit glycolysis. This may ultimately lead to a decrease in energy production. This may also decrease force production by impairing the cross-bridge formation between myofilaments.

Human Studies

Duffy and Conlee had 11 male subjects ingest 1.24 g of sodium acid phosphate and potassium phosphate 1 hour before exercise (acute) and 3.73 g/day of the phosphate combination for 6 days before exercise (chronic). Tread­mill endurance time, after 15 minutes of recovery from the first exercise, and oxygen uptake during the treadmill exercise, were measured. Running times ranged from 172­183 seconds during the first run and 145-152 seconds during the second run. Oxygen uptake averaged 52 mL/ kg/min during all conditions. The results showed no significant effect of acute or chronic ingestion of a combination of phosphates.

Bredle et al. conducted a double-blind, crossover experiment with 11 male runners. The subjects ingested 176 mmol/day of calcium phosphate or a placebo for 4 days. On day 3, subjects performed an incremental VO2max test on a treadmill, and on day 4, subjects ran on the treadmill at 70% VO2max until exhaustion. On day 4, plasma phosphate levels were significantly higher than in controls, but erythrocyte phosphate, 2,3-DPG, and oxygen half-saturation pressure of hemoglobin were unchanged. Also, neither VO2max nor sub maximal run time to exhaustion was changed by the treatment.

Treatment with phosphate increased the arteriovenous oxygen difference. The authors concluded that phosphates improve some cardiovascular functions, but do not have an effect on aerobic power.

Thirty endurance-trained males were studied for 364 days. Ten control subjects exercised 14.4 km/day at 10,000 steps/day. The other 20 subjects exercised less than 2.9 km/day (3000 walking steps/day) with half of them consuming phosphate, fluid, and salt. The results showed that hyperhydration and phosphate supplementation could minimize phosphate loss in endurance-trained subjects during periods of low exercise routines.

Conversely, when ten well-trained distance runners were given a phosphate load or a placebo for 3 days, the results were different. Pre- and post-measures included plasma phosphate concentration, RBC 2,3-DPG, hematocrit and hemoglobin concentrations, and degree of lactic acidemia. Blood samples for the control condition were drawn before and after a warm-up, after treadmill exercise at a 10% grade, and after the completion of the VO2max determination. Serum phosphate and RBC 2,3-DPG levels were significantly increased after the ingestion of phosphate. Also, VO2max was significantly increased and correlated with the rise in RBC 2,3-DPG .

Next, eight trained cyclists participated in three cycle ergometer tests after consuming phosphate, placebo, or no supplement. time to exhaustion, serum 2,3­DPG, and serum phosphate levels were measured before and after treatment. Serum phosphate levels did not change in any group, but there were increases in 2,3-DPG during phosphate supplementation. There was also a significant difference and time to exhaustion .

Moreover, Krieder et al. had seven male competitive runners participate in a two­session, placebo-controlled, double-blind study on phosphate loading. Oxygen uptake, ventilatory anaerobic thresh-old, and 5-mile performance were randomly tested on day 3 or day 6 after supplementation with tribasic sodium phosphate four times per day for 6 days. Phosphate loading significantly increased resting and post-exercise serum phosphate concentrations and also significantly increased maximum oxygen uptake (4.77-5.18 L/min) and ventilatory anaerobic threshold . Five-mile run times were different between sessions, but not significantly; however, mean performance run oxygen uptake was significantly lower with the ingestion of phosphate.

Two years later, Kreider et al had six male cyclists and triathletes consume 1 g of tribasic sodium phosphate or a glucose placebo four times per day for 3 days before exercise. The exercise consisted of an incremental maximal cycling test or a simulated 40-km time trial on a computerized race simulator. The subjects continued supplementation for 1 extra day, and performed the same exercise again. Metabolic data were collected during 15-second intervals and venous blood samples were collected during each stage of the cycling test and every 8 km during the run. The results showed that the phosphates increased anaerobic threshold, myocardial ejection fraction and fractional shortening, VO2max (69.3 versus 75.4 mL/kg/min for placebo and phosphate groups, respectively).

A fair amount of data have been collected on the use of phosphates as an endurance enhancer. With proposed mechanisms such as increasing oxidative phosphorylation, phosphocreatine synthesis, 2,3-DPG production, and also decreasing blood pH, it would seem plausible that phosphates would increase endurance performance. Currently, the data are mixed, with some studies showing an improvement in endurance performance and others showing no improvement. Phosphates do seem to have some potential as an ergogenic aid, but more studies are needed to prove this.