title: Increasing humidity affects thermoregulation during low-intensity exercise in women.
abstract: BACKGROUND
  Women increasingly occupy manual labor jobs. However, research examining women working under hot-humid conditions is lacking. Therefore, the purpose of our study was to assess how increasing relative humidity (RH) affects women's thermoregulation during low-intensity exercise characteristic of 8 h self-paced manual labor.
  
  
  METHODS
  There were 10 women (age: 23 ± 2 yr; body-surface area: 1.68 ± 0.13 m²; Vo2max: 46 ± 6 ml · kg⁻¹ · min⁻¹) who walked 90 min at 35% Vo2max in 35°C at 55% RH (55RH), 70% RH (70RH), and 85% RH (85RH). Investigators obtained: 1) rectal temperature (Tre), mean-weighted skin temperature (Tsk), and heart rate every 5 min; and 2) respiratory measures every 30 min.
  
  
  RESULTS
  Heat production (H) and required rate of evaporative cooling (Ereq) remained constant among trials; each RH increment significantly decreased evaporative heat loss (E), but increased heart rate and sweat rate. All other calorimetric and thermometric variables were similar between 55RH and 70RH, but significantly greater in 85RH. Tre only exceeded 38°C in 85RH after walking ∼80 min. Combined, dry and respiratory heat losses only compensated for <30% of the decreases in E.
  
  
  CONCLUSIONS
  Women exercising at low intensities in 35°C experienced most statistically significant physiological changes after 70RH. As H and Ereq remained constant across trials, heat storage increased with each 15% rise in RH because dry and respiratory heat losses minimally offset decreased E. Higher Tre, Tsk, and resultantly higher sweat rates reflected heat storage increases as E decreased in each trial. Overall, at 35°C Ta, we found women exercising for 90 min at low intensities remained at safe rectal temperatures up to 70% RH.
authors.affiliation: Exercise Physiology Laboratory, Department of Kinesiology, California State University, Fullerton, CA, USA.
authors.forename: Nicole E
authors.initials: NE
authors.lastname: Moyen
authors.forename: Toby
authors.initials: T
authors.lastname: Mündel
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Du Bois
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Ciccone
authors.forename: R Hugh
authors.initials: RH
authors.lastname: Morton
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Judelson
mesh_terms: D001833:Body Temperature Regulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D006813:Humidity; D008991:Monitoring, Physiologic / Q000379:methods*; D010101:Oxygen Consumption / Q000502:physiology; D013546:Sweating / Q000502:physiology; D055815:Young Adult