[Hydration status and aerobic capacity: effects on plasmatic volume during strenuous physical exercise]

During exercise, water loss frequently occurs in the intracellular spaces and there is a decrease in the plasmatic volume, with a blood concentration as a secondary characteristic. Plasmatic volume losses provoke a decrease in the blood flow, which directly affects cardiac function. Physical performance decreases and aerobic capacity deteriorates.

An observational, prospective, longitudinal, and comparative study was carried out to evaluate gender influence and the aerobic capacity level upon hydration and the plasmatic volume produced by maximal physical exercise. Twenty four individuals between 18 and 35 years old were included. All participated in aerobic physical exercise and changes in hemoglobin, hematocrit, plasmatic volume, and hydration state were evaluated.

Gender showed a significant influence on plasmatic volume but not on the hydration state. The aerobic capacity presented a relationship with plasmatic volume, and the plasmatic volume with the hydration state. Women presented more plasmatic volume loss than men (p < 0.05). Individuals who have adequate aerobic capacity tend to lose less plasmatic volume during exercise.

Maximal physical exercise during a short period also leads to important liquid loss; therefore, it is important that people who engage in exercise understand their liquid losses and re-hydrate themselves appropriately before, during, and after exercise.