title: Warm skin alters cardiovascular responses to cycling after preheating and precooling.
abstract: OBJECTIVE
  Exercise in hot conditions increases core (TC) and skin temperature (TSK) and can lead to a progressive rise in HR and decline in stroke volume (SV) during prolonged exercise. Thermoregulatory-driven elevations in skin blood flow (SkBF) adds complexity to cardiovascular regulation during exercise in these conditions. Presently, the dominant, although debated, view is that raising TSK increases SkBF and reduces SV through diminished venous return; however, this scenario has not been rigorously investigated across core and skin temperatures. We tested the hypothesis that high TSK would raise HR and reduce SV during exercise after precooling (cold water bath) and preheating (hot water bath) and that no relationship would exist between SkBF and SV during exercise.
  
  
  METHODS
  Non-endurance-trained individuals cycled for 20 min at 69% ± 1% VO₂peak on four occasions: cool skin-cool core (SkCCC), warm skin-cool core (SkWCC), cool skin-warm core (SkCCW), and warm skin-warm core (SkWCW) on separate days.
  
  
  RESULTS
  After precooling of TC, the rise in HR was greater in SkWCC than in SkCCC (P < 0.001), yet SV was similar (P = 0.26), which resulted in higher QC at min 20 in SkWCC (P < 0.01). Throughout exercise after preheating of TC, HR was higher (P < 0.001), SV was reduced (P < 0.01), and QC was similar (P = 0.40) in SkWCW versus SkCCW. When all trials were compared, there was no relationship between SkBF and SV (r = -0.08, P = 0.70); however, there was an inverse relationship between HR and SV (r = -0.75, P < 0.001).
  
  
  CONCLUSIONS
  These data suggest that when TSK is elevated during exercise, HR and TC will rise but SV will only be reduced when TC is also elevated above 38°C. Furthermore, changes in SV are not related to changes in SkBF.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, TX.
authors.forename: Joshua F
authors.initials: JF
authors.lastname: Lee
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Christmas
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Machin
authors.forename: Blake D
authors.initials: BD
authors.lastname: McLean
authors.forename: Edward F
authors.initials: EF
authors.lastname: Coyle
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D003080:Cold Temperature; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D012867:Skin / Q000098:blood supply; D012881:Skin Temperature / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology