title: Does intramuscular thermal feedback modulate eccrine sweating in exercising humans?
abstract: OBJECTIVE
  Few investigators have considered the possibility that skeletal muscles might contain thermosensitive elements capable of modifying thermoeffector responses. In this experiment, the temporal relationships between dynamic changes in deep-body and intramuscular temperatures and eccrine sweat secretion were explored during rhythmical and reproducible variations in heat production.
  
  
  METHODS
  Eight subjects performed semi-recumbent cycling (25 °C) at a constant load to first establish whole-body thermal and sudomotor steady states (35 min), followed by a 24-min block of sinusoidal workload variations (three, 8-min periods) and then returning to steady-state cycling (20 min). Individual oesophageal, mean skin and intramuscular (vastus lateralis) temperatures were independently cross-correlated with simultaneously measured forehead sweat rates to evaluate the possible thermal modulation of sudomotor activity.
  
  
  RESULTS
  Both intramuscular and oesophageal temperatures showed strong correlations with sinusoidal variations in sweating with respective maximal cross-correlation coefficients of 0.807 (±0.044) and 0.845 (±0.035), but these were not different (P = 0.40). However, the phase delay between intramuscular temperature changes and sweat secretion was significantly shorter than the delay between oesophageal temperature and sweating [25.6 s (±12.6) vs. 46.9 s (±11.3); P = 0.03].
  
  
  CONCLUSIONS
  The temporal coupling of eccrine sweating to intramuscular temperature, combined with a shorter phase delay, was consistent with the presence of thermosensitive elements within skeletal muscles that appear to participate in the modulation of thermal sweating.
authors.affiliation: Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Todd
authors.forename: C J
authors.initials: CJ
authors.lastname: Gordon
authors.forename: H
authors.initials: H
authors.lastname: Groeller
authors.forename: N A S
authors.initials: NA
authors.lastname: Taylor
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D004439:Eccrine Glands / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D025461:Feedback, Physiological; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D013546:Sweating / Q000502:physiology*
keywords: core temperature; exercise; muscle temperature; sweating; thermoregulation