title: Do greater rates of body heat storage precede the accelerated reduction of self-paced exercise intensity in the heat?
abstract: OBJECTIVE
  To reevaluate the previous hypothesis that greater reductions in self-paced exercise intensity in the heat are mediated by early differences in the rate of body heat storage (S).
  
  
  METHODS
  Eight trained volunteers cycled in 19 °C/1.8 kPa (COOL), 25 °C/1.2 kPa (NORM), and 34 °C/1.6 kPa (HOT), while maintaining an RPE of 16. Potential differences in S following the onset of exercise were assessed by comparing rates of esophageal temperature change (ΔT es/Δt); and estimated S values using a traditional two-compartment thermometric model (S therm) of changes in rectal (T re) and skin (T sk) temperature, and partitional calorimetry (S cal).
  
  
  RESULTS
  After 15 min of exercise, workload decreased more in HOT vs. COOL (P = 0.03), resulting in a shorter time (HOT: 40.7 ± 14.9 min; COOL: 53.5 ± 18.7 min; P = 0.04) to 70 % of initial workload. However, there were no preceding differences in ΔT es/Δt between conditions (P = 0.18). S therm values were different between HOT and COOL during the first 5 min of exercise (P < 0.05), primarily due to negative S therm values (-32 ± 15 kJ min(-1)) in COOL, which according to partitional calorimetric measurements, required improbably high (~56 kJ min(-1)) rates of evaporation when no sweating on the back and thigh was observed until after 7.6 ± 1.5 min and 4.8 ± 1.7 min of exercise, respectively. S cal values in the first 5 min of exercise confirmed S was actually positive in COOL (+21 ± 8 kJ min(-1)) and not negative. Different S therm values following the onset of exercise at different environmental temperatures are simply due to transient differences in the rate of change in T sk.
  
  
  CONCLUSIONS
  Reductions in self-paced exercise intensity in the heat are not mediated by early differences in S following the onset of exercise.
authors.affiliation: Thermal Ergonomics Laboratory, School of Human Kinetics, University of Ottawa, 200 Lees Ave, Ottawa, K1N 6N5, Canada.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Ravanelli
authors.forename: Matthew N
authors.initials: MN
authors.lastname: Cramer
authors.forename: Yannick
authors.initials: Y
authors.lastname: Molgat-Seon
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Carlsen
authors.forename: Ollie
authors.initials: O
authors.lastname: Jay
mesh_terms: D000328:Adult; D001833:Body Temperature Regulation; D015444:Exercise / Q000502:physiology*; D017079:Exercise Tolerance; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male
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