【Research Review】Heat Acclimation Training and Its Effects on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: Advances in Exercise Physiology Research (Article 625)

Reference Journal Source: 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 improves both “heat dissipation capacity” and “athletic performance”: before plasma volume expansion, the body must compete between “blood supply to muscles” and “blood supply to skin for heat dissipation”; after adaptation, this competition is substantially 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 observations can be made:

• 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 magnitude of core temperature rise becomes smaller, and resting heart rate decreases

Heat Adaptation Days and Changes in Physiological Indicators (Illustrative)

Key Scientific Conclusions and Practical Recommendations

• Exposure Methods: Adaptation can be accelerated through training in actual hot environments, or by scheduling passive heat exposure via hot baths/saunas after training in mild environments
• Electrolyte Supplementation: 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 simultaneous surge of core temperature and cardiovascular load, which could pose a risk of heat stroke
• Adaptation Decays: The effects of heat adaptation gradually diminish approximately 1-3 weeks after cessation of exposure; the pre-competition heat acclimation block should be scheduled so that the main adaptation period is 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 athletes expected to compete in hot and humid environments. If the race location has a cool climate, the marginal benefit of heat acclimation decreases, but plasma volume expansion itself still provides positive benefits for general endurance performance.

Q: Can a sauna replace actual heat training?

A: It can serve as an adjunct method; passive heat exposure can indeed induce some adaptive responses, but it cannot fully replace the training-specific adaptations that occur when “exercise plus heat” happen simultaneously. Combining both approaches is recommended.

References and Academic Citations

1. Journal of Applied Physiology — Research related to the mechanisms of heat adaptation and plasma volume regulation.
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: Advances in Exercise Physiology Research (Article 274)
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