[Research Review] Study on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners Through Heat Acclimation: International Scientific Literature Compilation and Review (No. 454)

Reference Journal Source: Journal of Applied Physiology • International Scientific Research Review Series

This article explores the physiological mechanisms of Heat Acclimation (HA) regarding plasma volume expansion and core temperature regulation in marathon runners.

Physiological Mechanisms of Plasma Volume Expansion

Repeated heat exposure stimulates the kidneys and endocrine system to release antidiuretic hormone and aldosterone, prompting the body to retain more water and sodium, thereby expanding plasma volume. Once plasma volume increases, both skin blood flow and muscle blood flow can be more adequately supplied at the same cardiac output—this is the key to how heat adaptation simultaneously improves “heat dissipation capacity” and “athletic performance.” Before plasma volume expansion, the body must compete between “muscle blood supply” and “skin heat dissipation blood supply”; after adaptation, this competitive relationship is significantly alleviated.

The Adaptation Process of Core Temperature Regulation

The complete process of heat adaptation typically requires 10-14 days of repeated exposure. During the adaptation process, the following can be observed:

• A decrease in the temperature threshold for the onset of sweating (sweating begins earlier, making the heat dissipation response more sensitive).
• An increase in the sweat rate per unit of time, while the sodium concentration in the sweat decreases (reducing electrolyte loss).
• At the same exercise intensity, the rise in core temperature becomes smaller, and resting heart rate decreases.

Heat Adaptation Days and Physiological Indicator Changes (Illustration)

Key Scientific Conclusions and Practical Recommendations

• Exposure Methods: Adaptation can be accelerated through actual high-temperature environment training, or by arranging passive heat exposure such as hot baths/saunas after training in mild environments.
• Electrolyte Supplementation: Sweat volume increases significantly during the adaptation period; the frequency of sodium and water supplementation should be increased to avoid the risk of hyponatremia.
• Progressive Approach: Initial heat adaptation training should reduce exercise intensity to avoid the simultaneous spike in core temperature and cardiovascular load, which could lead to heatstroke.
• Adaptation Fades: The effects of heat adaptation gradually fade within about 1-3 weeks after stopping exposure. Pre-race heat adaptation schedules should be arranged so that the main adaptation period is completed within 2 weeks before the race.

Common Scientific FAQs

Q: Is heat adaptation training suitable for all marathon runners?

A: It is most beneficial for runners expected to compete in hot and humid environments. If the race climate is cool, the marginal benefit of heat adaptation is reduced, but plasma volume expansion itself still has positive benefits for general endurance performance.

Q: Can a sauna replace actual high-temperature training?

A: It can be used as an auxiliary tool. Passive heat exposure can indeed induce some adaptive responses, but it cannot fully replace the training-specific adaptation that occurs when “exercise + heat” happen simultaneously. It is recommended to use both in combination.

References and Academic Citations

1. Journal of Applied Physiology — Research directions related to heat adaptation and plasma volume regulation mechanisms.
2. Scandinavian Journal of Medicine & Science in Sports — Literature related to the intervention effects of heat adaptation training for endurance athletes.

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