Dietary sodium intake and changes in plasma volume during short-term exercise training.

Abstract

This study was a retrospective examination of the relationship between estimated dietary sodium intake and training-induced changes in plasma volume (PV). It was undertaken to explore one possible explanation for the large individual differences in PV shifts accompanying 3 d of endurance cycling. Ten healthy males rode a stationary cycle for an average time of 94 min/day at an average relative intensity of 68% VO2max. During the training period, the subjects were allowed to eat a diet of their own choosing and dietary sodium intake was estimated from diet records. Plasma volume was determined before and after short-term training by dye dilution using Evan's blue dye. The mean increase in PV was 4.53 ml.kg body weight (BW)-1 (i.e. 11%). However, the individual shifts in PV ranged from -1.44-14.30 ml.kg BW-1. The correlation coefficient between estimated dietary sodium intake and changes in PV was 0.81. It was concluded that dietary sodium intake was strongly associated with training-induced shifts in PV and may be an influential factor in determining the magnitude of PV expansion derived from short-term exercise training. Further studies are needed, however, to examine this hypothesis.