[Research Review] Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: An International Scientific Literature Translation and Review Report (No. 559)

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

This article explores the physiological mechanisms by which heat acclimation training affects plasma volume expansion and core temperature regulation adaptation 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 ions, thereby expanding plasma volume. With increased plasma volume, under the same cardiac output, skin blood flow and muscle blood flow can both receive more adequate supply simultaneously—this is precisely the key to how heat adaptation simultaneously improves “heat dissipation capacity” and “exercise performance”: before plasma volume expansion, the body must compete between “muscle blood supply” and “skin heat-dissipation blood supply”; after adaptation, this competition is significantly alleviated.

The Adaptation Process of Core Temperature Regulation

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

• The core temperature threshold for sweat onset decreases (sweating begins earlier, and the heat dissipation response becomes more sensitive)
• Sweat rate per unit time increases, but sodium ion concentration in sweat decreases (reducing electrolyte loss)
• At the same exercise intensity, the rise in core temperature is smaller, and resting heart rate decreases

Heat Adaptation Days and Physiological Indicator Changes (Illustrative)

Key Scientific Conclusions and Practical Recommendations

• Exposure Method: Adaptation can be accelerated through training in actual hot environments, or by scheduling additional passive heat exposure via hot baths/saunas after training in milder environments
• Electrolyte Supplementation: Since sweat rate increases substantially during the adaptation period, the frequency of sodium and fluid intake should be increased to avoid the risk of hyponatremia
• Progressive Approach: Exercise intensity should be reduced during the initial phase of heat adaptation training to avoid the risk of heat stroke from a simultaneous spike in core temperature and cardiovascular load
• Adaptation Decays: The effects of heat adaptation gradually diminish approximately 1-3 weeks after cessation of exposure; the main adaptation phase of a pre-race heat acclimation schedule should be completed within 2 weeks before race day

Common Research Q&A (FAQ)

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

A: The benefits are most pronounced for runners planning to compete in hot, humid environments. If the race location has a cool climate, the marginal benefit of heat adaptation decreases, but plasma volume expansion itself still provides positive assistance to general endurance performance.

Q: Can saunas replace actual heat training?

A: Saunas can serve as a supplementary method; passive heat exposure can indeed induce some adaptive responses, but it cannot fully replace the training-specific adaptations that occur when “exercise and 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 effects of heat acclimation training interventions in endurance athletes.

Related Reading

• Research Review: Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: An International Scientific Literature Translation and Review Report (No. 805)
• Research Review: Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: An International Scientific Literature Translation and Review Report (No. 802)
• Research Review: Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: An International Scientific Literature Translation and Review Report (No. 679)
• Research Review: Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: An International Scientific Literature Translation and Review Report (No. 454)