Hypervolemia in men from drinking hyperhydration fluids at rest and during exercise

To test the hypothesis that drink composition is more important than drink osmolality (Osm) for maintaining and increasing plasma volume (PV) at rest and during exercise, six men (22-39 yr, 76.84 +/- 16.19 kg, 2.99 +/- 0.45 L/min VO2 peak) each underwent six treatments while sitting for 90 min (VO2 = 0.39 L/min) and then performed upright ergometer exercise for 70 min (VO2 = 2.08 +/- 0.33 1/min, 70% +/- 7% VO2 peak). Drink formulations (10 ml/kg body weight, X = 768 ml) for the sitting period were: P1 (55 mEq Na(+), 365 mOsm/kg H2O), P2 (97.1 mEq Na(+), 791 mOsm/kg), P2G (113 mEqNa(+), 80 ml glycerol, 1,382 mOsm/kg, HyperAde (HA) (164 mEq Na(+), 253 mOsm/kg), and 01 and 02 (no drinking). The exercise drink (10 ml/kg, 768 ml) was P1 for all treatments except 02. Plasma volume at rest increased (p less than 0.05) by 4.7% with P1 and by 7.9% with HA. Percent change in PV during exercise was +1% to +3%0(NS) with HA; -6% to 0% (NS) with P1, P2, P2G, and 01; and -8% to -5% (p less than 0.05) with 02. HyperAde, with the lowest osmolality (253 mOsm/kg), maintained PV at rest and during exercise, whereas the other drinks with lower Na(+) and higher osmolality (365 to 1,382 mOsm/kg) did not. But Performance 1 also increased PV at rest. Thus, drink composition may be more important than drink osmolality for increasing plasma volume at rest and for maintaining it during exercise.