[Research Review] Study on Heat Acclimation Training for Marathon Runners’ Plasma Volume Expansion and Core Temperature Adaptation: International Scientific Literature Translation and Review Report (No. 1411)

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

This article explores the physiological mechanisms of heat acclimation training on 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 “athletic performance”: before plasma volume expansion, the body must compete between “muscle blood supply” and “skin heat dissipation blood supply”; after adaptation, this competition is substantially alleviated.

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 observations can be made:

• The core temperature threshold for sweat onset decreases (sweating begins earlier, 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 magnitude of core temperature rise diminishes, and resting heart rate decreases

Heat Adaptation Days and Physiological Indicator Changes (Illustrative)

Core Scientific Conclusions and Practical Recommendations

• Exposure Methods: Adaptation can be accelerated through training in actual hot environments, or by scheduling additional passive heat exposure via hot baths/saunas after training in mild environments
• Electrolyte Supplementation: Sweat rate increases substantially during the adaptation period; sodium and fluid supplementation frequency 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 simultaneous surge of core temperature and cardiovascular load that could cause heat stroke risk
• Adaptation Decays: The effects of heat adaptation gradually diminish approximately 1-3 weeks after cessation of exposure; pre-race heat adaptation schedules should complete the main adaptation period within 2 weeks before the competition

Common Research Q&A (FAQ)

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

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

Q: Can saunas replace actual heat training?

A: They can serve as an auxiliary method—passive heat exposure can indeed induce some adaptive responses—but they cannot fully replace the training-specific adaptations that occur 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 on the effects of heat acclimation training interventions in endurance athletes.

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