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Published on: March 15, 2019
Effect of initial core temperature on hyperthermic hyperventilation during prolonged submaximal exercise in the heat
Bun Tsuji1, Yasushi Honda, Naoto Fujii
1Institute of Health and Sports Science, University of Tsukuba, Tsukuba City, Ibaraki, Japan.
Summary
Exercise in heat triggers increased breathing (hyperventilation) once core body temperature surpasses a specific threshold. This response remains consistent regardless of starting body temperature, indicating a fixed trigger point for heat-induced hyperventilation during exercise.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Human Thermoregulation
Background:
- Hyperthermic hyperventilation, an increase in breathing rate due to elevated body temperature, is a known physiological response during exercise.
- The existence of a specific core temperature threshold and its dependence on initial body temperature during prolonged exercise in heat remain areas of investigation.
Purpose of the Study:
- To determine if a core temperature threshold for hyperthermic hyperventilation exists during prolonged submaximal exercise in the heat.
- To investigate whether altering the initial core temperature affects the hyperventilatory response during exercise in the heat.
Main Methods:
- Ten male subjects underwent three exercise trials at 50% peak oxygen uptake in hot conditions (37°C, 50% RH).
- Initial esophageal temperature (T(es)) was manipulated via 25-minute water immersion at 18°C (Precooling), 35°C (Control), or 40°C (Preheating).
- Minute ventilation (Ve) and T(es) were continuously monitored throughout the exercise duration.
Main Results:
- A distinct core temperature threshold for hyperthermic hyperventilation was observed in the Precooling trial (37.1 ± 0.4°C).
- Minute ventilation increased linearly with core temperature above this threshold across all trials.
- The sensitivity of ventilation to increasing core temperature (T(es)-Ve relation slope) was not significantly different between Precooling, Control, and Preheating conditions.
Conclusions:
- A clear core temperature threshold for hyperthermic hyperventilation exists during prolonged submaximal exercise in the heat.
- The magnitude of the hyperventilatory response to increasing core temperature is independent of the initial core temperature before exercise.
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