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Water balance during and after marathon running
J Pastene1, M Germain, A M Allevard
1Service de Biologie et M7edecine du Sport, Chemin du Grand Revojot, Centre Hospitalier Lyon-Sud, France.
Summary
Plasma volume did not significantly decrease during marathon running, despite body mass loss. Hormone levels changed due to exercise, not dehydration, with plasma volume expanding post-race.
Area of Science:
- Exercise Physiology
- Endocrinology
- Sports Science
Background:
- Marathon running causes significant physiological stress.
- Understanding plasma volume and hormonal responses is crucial for athlete health and performance.
- Dehydration is a common concern during endurance events.
Purpose of the Study:
- To investigate plasma volume changes during and after marathon running.
- To analyze the time course of hormones regulating water balance.
- To differentiate exercise effects from dehydration effects on hormonal responses.
Main Methods:
- Studied six experienced marathon runners during a treadmill marathon.
- Measured haematocrit, haemoglobin, plasma protein, electrolytes, osmolality, renin, aldosterone, and ANP.
- Collected samples at rest, during the race, and up to 72 hours post-race.
Main Results:
- Plasma volume, protein, osmolality, and sodium showed no significant changes during the race.
- Potassium, renin, and aldosterone increased significantly by the end of the race.
- Body mass decreased by 2.0 kg, despite fluid intake; urinary output and sodium excretion dropped post-race.
- Plasma volume significantly increased 24-48 hours post-race.
Conclusions:
- The lack of plasma volume decrease during the marathon was attributed to metabolic and glycogen-stored water.
- Hormonal responses were likely due to exercise intensity rather than dehydration.
- Post-marathon plasma volume expansion resulted from protein shift and renal sodium retention.