Mild hypohydration induced by exercise in the heat attenuates autonomic thermoregulatory responses to the heat, but not thermal pleasantness in humans

Ken Tokizawa, Saki Yasuhara, Mayumi Nakamura, Yuki Uchida, Larry I. Crawshaw, Kei Nagashima

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    Abstract

    Hypohydration caused by exercise in the heat attenuates autonomic thermoregulation such as sweating and skin blood flow in humans. In contrast, it remains unknown if behavioral thermoregulation is modulated during hypohydration. We assume that thermal unpleasantness could drive the behavioral response, and would also be modulated during hypohydration. Nine healthy young men participated in the present study. Body and skin temperatures were monitored. Ratings of thermal sensation and pleasantness were conducted. After ~45. min rest at 27°C, they performed 50-min cycling exercise, which was at the level of 40% of heart rate range at 35°C (hypohydration trial) or at the level of 10% of heart rate range at 23°C (control trial), respectively. Subjects returned to the rest at 27°C, and the ambient temperature was then changed from 22 to 38°C. Body weight decreased by 0.9 ± 0.1% immediately after exercise in the hypohydration trial and 0.3 ± 0.1% in the control trial. In the cold, no significant difference in thermal sensation or pleasantness was observed between trials. There was no significant difference in thermal pleasantness between trials in the heat, although thermal sensation in the heat (32.5-36°C) was significantly lower in the hypohydration trial than in the control trial. In addition, laser Doppler flow of the skin and sweat rate were attenuated in the heat in the hypohydration trial. These results may indicate that mild hypohydration after exercise in the heat has no influence on behavioral responses to the heat.

    Original languageEnglish
    Pages (from-to)340-345
    Number of pages6
    JournalPhysiology and Behavior
    Volume100
    Issue number4
    DOIs
    Publication statusPublished - 2010 Jun

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    Keywords

    • Behavioral thermoregulation
    • Exercise
    • Hyperosmolality
    • Hypohydration
    • Thermal perception
    • Thermal pleasantness

    ASJC Scopus subject areas

    • Behavioral Neuroscience
    • Experimental and Cognitive Psychology

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