Exercise thermoregulation after 6 h of chair rest, 6° head-down bed-rest, and water immersion deconditioning in men

  • J. E. Greenleaf
  • T. Hutchinson
  • M. Shaffer-Bailey
  • R. Looft-Wilson
Original Article

Abstract

The purpose was to investigate the mechanism for the excessive exercise hyperthermia following deconditioning (reduction of physical fitness). Rectal (Tre) and mean skin (\(\bar T_{sk}\)) temperatures and thermoregulatory responses were measured in six men [mean (SD) age, 32 (6) years; mass, 78.26 (5.80) kg; surface area, 1.95 (0.11)m2; maximum oxygen uptake (\(\dot VO_{2max}\)), 48 (6) ml·min−1·kg−1; whilst supine in air at dry bulb temperature 23.2 (0.6)°C, relative humidity 31.1 (11.1)% and air speed 5.6 (0.1) m·min−1] during 70 min of leg cycle exercise [51 (4)%\(\dot VO_{2max}\)] in ambulatory control (AC), or following 6 h of chair rest (CR), 6° head-down bed rest (BR), and 20° (WI20) and 80° (WI80) foot-down water immersion [water temperature, 35.0 (0.1)°C]. Compared with the AC exercise ΔTre [mean (SD) 0.77 (0.13)°C], ΔTre after CR was 0.83 (0.08)°C (NS), after BR 0.92 (0.13)°C (*P<0.05), after WI80 0.96 (0.13)°C*, and after WI20 1.03 (0.09)°C*. All\(\bar T_{sk}\) responded similarly to exercise: they decreased (NS) by 0.5–0.7°C in minutes 4–8 and equilibrated at +0.1 to +0.5°C at 60–70. Skin heat conductance was not different among the five conditions (range = 147–159 kJ·m−2·h−1·°C−1). Results from an intercorrelation matrix suggested that total body sweat rate was more closely related toTre at 70 min (Tre70) than limb sweat rate or blood flow. Only 36% of the variability inTre70 could be accounted for by total sweating, and less than 10% from total body dehydration. It would appear that multiple factors are involved which may include change in sensitivity of thermo- and osmoreceptors.

Key words

Rectal temperature Mean skin temperature Blood flow Thermoregulation Deconditioning 

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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • J. E. Greenleaf
    • 1
  • T. Hutchinson
    • 1
  • M. Shaffer-Bailey
    • 1
  • R. Looft-Wilson
    • 1
  1. 1.Laboratory for Human Environmental Physiology (239-11), Gravitational Research BranchNASA, Ames Research CenterMoffett FieldUSA

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