Exercise-Induced Hypervolemia may not be Consequential to Dehydration During Exercise.

Area of Science:

• Exercise Physiology
• Sports Science
• Human Physiology

Background:

• Plasma volume (PV) expansion is a common adaptation following exercise.
• The relationship between exercise-induced dehydration and subsequent PV expansion requires further investigation.

Purpose of the Study:

• To determine if the magnitude of dehydration during exercise is proportional to the plasma volume expansion observed 24 hours post-exercise.
• To investigate the physiological stimuli for exercise-induced hypervolemia.

Main Methods:

• Seven male participants completed three cycling sessions at 50% peak power output in hot conditions (35°C, 50% RH) for 30, 60, or 90 minutes.
• Dehydration was assessed by body mass changes, and plasma volume changes were calculated 24 hours after each session.
• Regression analysis was used to correlate percent dehydration with percent change in plasma volume.

Main Results:

• Body mass decreased by 1.03%, 1.43%, and 1.59% following 30, 60, and 90 minutes of exercise, respectively.
• No significant plasma volume expansion was observed 24 hours after any exercise protocol (ranging from 0.76% to 2.92%).
• A poor correlation (r=0.24) was found between the percent dehydration and the percent change in plasma volume.

Conclusions:

• The levels of dehydration achieved in this study were insufficient to stimulate a significant increase in plasma volume.
• Strategies to prolong post-exercise hypotension or delay hydration may be necessary to evoke observable plasma volume expansion.
• Further research is needed to fully understand the stimuli for exercise-induced hypervolemia for effective prescription by exercise physiologists.