Fluid and electrolyte homeostasis during prolonged exercise at altitude

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Fluid and Electrolyte Balance

Background:

• Understanding fluid and electrolyte homeostasis during combined exercise and altitude exposure is crucial for athletes and military personnel.
• Previous research indicates that exercise and altitude independently affect fluid balance, but their combined impact requires further elucidation.

Purpose of the Study:

• To investigate the effects of combined exercise and high altitude on fluid and electrolyte balance in male subjects.
• To compare these effects with those of exercise at sea level and altitude exposure without exercise.

Main Methods:

• Six male subjects underwent a 13-day study with controlled sodium and potassium intake.
• Subjects were exposed to moderate altitude (900 m) initially and finally, with an intermediate 5-day period of strenuous hill walking (7 h/day) at higher altitudes (2,678–3,629 m).
• Fluid and electrolyte balance, plasma volume, and packed cell volume were monitored.

Main Results:

• A significant retention of sodium (202 mM) and water (0.49 L) was observed during the exercise-altitude period.
• Plasma volume increased by 0.76 L, while packed cell volume decreased from 44.5% to 41.8%.
• Extracellular space expanded by 1.44 L at the expense of intracellular space, which decreased by 1.05 L, with no change in plasma sodium concentration.

Conclusions:

• Combined exercise and altitude exposure lead to sodium and water retention, expanding extracellular fluid volume.
• These physiological adaptations are comparable to exercise at sea level and counteract the typical effects of altitude on resting individuals.
• The findings highlight the body's adaptive mechanisms to maintain fluid balance under strenuous environmental conditions.