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1 Institute of Health & Sports Science, University of Tsukuba, Tsukuba, Ibaraki, Japan
2 Faculty of Human Development, Kobe University, Kobe, Hyougo, Japan
* To whom correspondence should be addressed. E-mail: nisiyasu{at}taiiku.tsukuba.ac.jp.
We examined whether an increase in skin temperature or the rate of increase in core body temperature influences the relationship between minute ventilation (VE) and core temperature during prolonged exercise in the heat. Thirteen subjects exercised for 60 min on a cycle ergometer at 50% of peak oxygen uptake while wearing a suit perfused with water at 10°C (T10), 35°C (T35) or 45°C (T45). During the exercise, esophageal temperature (Tes), skin temperature, heart rate (HR), VE, tidal volume, respiratory frequency (fR), respiratory gases, blood pressure (BP) and blood lactate were all measured. We found that oxygen uptake, carbon dioxide output, BP and blood lactate did not differ among the sessions. Tes, HR, VE and fR remained nearly constant from minute 10 onward in the T10 session, but all of these parameters progressively increased in the T35 and T45 sessions, and significantly higher levels were seen in the T45 than the T35 session. For all but two subjects in the T35 and T45 sessions, plotting VE as a function of Tes revealed no threshold for hyperventilation; instead, increases in VE were linearly related to Tes, and there were no significant differences in the slopes or intercepts between the T35 and T45 sessions. Thus, during prolonged sub-maximal exercise in the heat, VE increases with core temperature, and the influences of skin temperature and the rate of increase in Tes on the relationship between VE and Tes are apparently small.
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