title: The effect of the menstrual cycle and water ingestion on physiological responses during prolonged exercise at moderate intensity under hot conditions.
abstract: OBJECTIVE
  Reproductive hormones are likely to be involved in thermoregulation through body fluid dynamics. In the present study, we aimed to investigate the effect of the menstrual cycle and water ingestion on physiological responses to prolonged exercise at moderate intensity under hot conditions.
  
  
  METHODS
  Eight healthy young women with regular menstrual cycles performed cycling exercise for 90 min at 50% VO2peak intensity during the low progesterone (LP) level phase and high progesterone (HP) level phase, with or without water ingestion, under hot conditions (30°C, 50% relative humidity). For the water ingestion trials, subjects ingested water equivalent to the loss in body weight that occurred in the earlier non-ingestion trial. For all four trials, rectal temperature, cardiorespiratory responses, and ratings of perceived exertion (RPE) were measured.
  
  
  RESULTS
  Throughout the 90-min exercise period, rectal temperatures during HP were higher than during LP by an average of 0.4°C in the non-ingestion trial (P < 0.01) and 0.2°C in the water ingestion trial (P < 0.05). During exercise, water ingestion affected the changes in rectal temperature and heat rate (HR) during HP, but it did not exert these effects during LP. Furthermore, we found a negative correlation between estradiol levels and rectal temperature during LP.
  
  
  CONCLUSIONS
  During prolonged exercise at moderate intensity under hot conditions, water ingestion is likely to be useful for suppressing the associated increase in body temperature and HR, particularly during HP, whereas estradiol appears to be useful for suppressing the increase in rectal temperature during LP.
authors.affiliation: Faculty of Sport Sciences, Waseda University, Saitama, Japan - hideki.hashimoto@asahiinryo.co.jp.
authors.forename: H
authors.initials: H
authors.lastname: Hashimoto
authors.forename: T
authors.initials: T
authors.lastname: Ishijima
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Higuchi