Dietary Sodium Intake and Changes in Plasma Volume During Short-Term Exercise Training

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 traiing. Further studies are needed, however, to examine this hypothesis.

Key words

Hypervolemia - Evan's blue dye - diet record