The effect of citrate loading on exercise performance, acid-base balance and metabolism

Summary

Nine subjects ($\dot V_{o_{2max} }$ 65±2 ml·kg⁻¹·min⁻¹, mean±SEM) were studied on two occasions following ingestion of 500 ml solution containing either sodium citrate (C, 0.300 g·kg⁻¹ body mass) or a sodium chloride placebo (P, 0.045 g·kg⁻¹ body mass). Exercise began 60 min later and consisted of cycle ergometer exercise performed continuously for 20 min each at power outputs corresponding to 33% and 66%$\dot V_{o_{2max} }$, followed by exercise to exhaustion at 95%$\dot V_{o_{2max} }$. Pre-exercise arterialized-venous [H⁺] was lower in C (36.2±0.5 nmol·l⁻¹; pH 7.44) than P (39.4±0.4 nmol·l⁻¹; pH 7.40); the plasma [H⁺] remained lower and [HCO ⁻₃ ] remained higher in C than P throughout exercise and recovery. Exercise time to exhaustion at 95%$\dot V_{o_{2max} }$ was similar in C (310±69 s) and P (313±74 s). Cardiorespiratory variables (ventilation,$\dot V_{o_2 }$,$\dot V_{CO_2 } v$, heart rate) measured during exercise were similar in the two conditions. The plasma [citrate] was higher in C at rest (C, 195±19 μmol·l⁻¹; P, 81±7 μmol·l⁻¹) and throughout exercise and recovery. The plasma [lactate] and [free fatty acid] were not affected by citrate loading but the plasma [glycerol] was lower during exercise in C than P. In conclusion, sodium citrate ingestion had an alkalinizing effect in the plasma but did not improve endurance time during exercise at 95%$\dot V_{o_{2max} }$. Furthermore, citrate loading may have prevented the stimulation of lipolysis normally observed with exercise and prevented the stimulation of glycolysis in muscle normally observed in bicarbonate-induced alkalosis.