[Research Digest] The Effect of Heat Acclimation Training on Plasma Volume Expansion and Core Temperature Adaptation in Marathon Runners: International Research Literature Translation and Digest Report (Episode 964)

This article examines the physiological mechanisms behind heat acclimation training and its effects on plasma volume expansion and core temperature regulation adaptation in marathon runners.

The Physiological Mechanism 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, skin blood flow and muscle blood flow can both be adequately supplied at the same cardiac output — this is precisely why heat acclimation improves both “heat dissipation capacity” and “athletic performance” simultaneously: before plasma volume expansion, the body must compete between “supplying muscle” and “supplying skin for cooling”; after adaptation, this competition is substantially eased.

The Adaptation Process of Core Temperature Regulation

A complete heat acclimation process typically requires 10-14 days of repeated exposure, during which the following are observed:

• A lower core temperature threshold for sweating onset (sweating begins earlier, a more responsive cooling reflex)
• Increased sweat rate per unit time, but with lower sodium concentration in sweat (reducing electrolyte loss)
• A smaller rise in core temperature at the same exercise intensity, and a lower resting heart rate

Illustrative Comparison of Acclimation Days and Physiological Indicator Changes

Core Research Findings and Practical Recommendations

• Exposure methods: acclimation can be accelerated either through actual training in hot environments, or by training in a mild environment followed by passive heat exposure such as a hot bath or sauna
• Electrolyte replenishment: sweat volume increases significantly during acclimation, so sodium and fluid intake frequency should be increased to avoid the risk of hyponatremia
• Gradual progression: early heat acclimation training should reduce exercise intensity to avoid simultaneously spiking core temperature and cardiovascular load, which raises heat stroke risk
• Adaptation fades: heat acclimation effects gradually fade within about 1-3 weeks after exposure stops — a pre-race heat acclimation program should complete its main adaptation phase within 2 weeks before the race

Frequently Asked Questions (FAQ)

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

A: The benefit is most pronounced for runners expecting to race in hot, humid conditions. If the race climate is cool, the marginal benefit of heat acclimation decreases, but plasma volume expansion itself still positively benefits general endurance performance.

Q: Can a sauna substitute for actual heat training?

A: It can serve as a supplementary method — passive heat exposure does trigger part of the adaptive response, but it cannot fully replace the training specificity of “exercise + heat” occurring simultaneously; combining both is recommended.

References and Academic Citations

1. Journal of Applied Physiology — research direction on heat acclimation 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.