Hypervolemia in men from fluid ingestion at rest and during exercise

Area of Science:

• Sports Science
• Human Physiology
• Fluid Balance

Background:

• Plasma osmolality (Osm) is crucial for regulating plasma volume (PV) and body water.
• While oral rehydration for dehydration is understood, optimal fluid composition for hyperhydration in normally hydrated individuals remains unclear.

Purpose of the Study:

• To investigate the impact of fluid composition versus osmolality on plasma volume expansion in euhydrated men.
• To determine the effectiveness of different oral fluid formulations in increasing PV at rest and maintaining it during exercise.

Main Methods:

• Six male subjects underwent six different oral fluid treatments (varying ionic and constituent concentrations) without and with fluid intake.
• Fluid intake involved 768 ml at rest and during 70 minutes of submaximal exercise.
• Treatments included varying sodium (Na+) concentrations and osmolalities, including AstroAde (AA) and Performance drinks (P1, P2, P2G).

Main Results:

• AstroAde (AA), with the lowest osmolality (253 mOsm.kg-1), significantly increased PV at rest (7.9%) and maintained it during exercise.
• Other formulations with higher osmolality (365-1382 mOsm.kg-1) did not maintain PV during exercise.
• P1 also increased PV at rest, but PV decreased during exercise across most treatments without AA.

Conclusions:

• Fluid composition, particularly sodium content and formulation, is more critical than osmolality for enhancing PV at rest.
• Specific drink formulations can effectively maintain PV during exercise in euhydrated individuals.