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Heat Acclimation Does Not Modify Q 10 and Thermal Cardiac Reactivity
Bernhard Kampmann1, Peter Bröde2
1Department of Occupational Health Science, School of Mechanical Engineering and Safety Engineering, University of Wuppertal, Wuppertal, Germany.
Frontiers in Physiology
|January 11, 2020
Summary
Heat acclimation (HA) does not alter the increase in energy expenditure or heart rate with rising body temperature. These physiological responses to heat stress are independent of heat acclimation status.
Area of Science:
- Environmental Physiology
- Human Heat Strain
- Occupational Health
Background:
- Heat acclimation (HA) is crucial for mitigating physiological strain in hot environments.
- The impact of HA on thermoregulatory responses like energy expenditure (Q10 effect) and heart rate (thermal cardiac reactivity - TCR) remains unclear.
- Understanding these effects is vital for workplace heat stress management.
Purpose of the Study:
- To investigate whether heat acclimation influences the Q10 effect on oxygen consumption (VO2) and thermal cardiac reactivity (TCR) in response to increased body temperature.
- To analyze the independent effects of rising core body temperature and heat acclimation status on VO2 and heart rate (HR).
Main Methods:
- Utilized a heat strain database from climatic chamber experiments involving five young males in both non-acclimated and acclimated states.
- Collected data on oxygen consumption (VO2), heart rate (HR), and rectal temperature (T_re) during constant workload (walking 4 km/h) under diverse heat stress conditions.
- Analyzed 273 trials using mixed-model ANCOVA to assess the influence of T_re and HA on VO2 and HR.
Main Results:
- Rising rectal temperature (T_re) significantly increased both VO2 (approx. 7% per °C) and HR (39-41 bpm per °C).
- These relationships between T_re and physiological responses (VO2, HR) were not significantly influenced by heat acclimation status (HA).
- Observed effects align with established Q10 (2) and TCR (33 bpm/°C) values.
Conclusions:
- The Q10 effect on energy expenditure and thermal cardiac reactivity are independent of heat acclimation.
- Findings suggest that current models for assessing heat stress and heat balance do not need adjustment for HA status.
- Implications for optimizing heat stress guidelines in occupational settings.
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