European Journal of Applied Physiology

, Volume 91, Issue 5, pp 729–736

Passive hyperthermia reduces voluntary activation and isometric force production

  • Shawnda Morrison
  • Gordon G. Sleivert
  • Stephen S. Cheung
Original Article

DOI: 10.1007/s00421-004-1063-z

Cite this article as:
Morrison, S., Sleivert, G.G. & Cheung, S.S. Eur J Appl Physiol (2004) 91: 729. doi:10.1007/s00421-004-1063-z

Abstract

It has been suggested that a critically high body core temperature may impair central neuromuscular activation and cause fatigue. We investigated the effects of passive hyperthermia on maximal isometric force production (MVC) and voluntary activation (VA) to determine the relative roles of skin (Tsk) and body core temperature (Tc) on these factors. Twenty-two males [O2max=64.2 (8.9) ml kg−1 min−1, body fat=8.2 (3.9)%] were seated in a knee-extension myograph, then passively heated from 37.4 to 39.4°C rectal temperature (Tre) and then cooled back to 37.4oC using a liquid conditioning garment. Voluntary strength and VA (interpolated twitch) were examined during an isometric 10-s MVC at 0.5°C intervals during both heating and cooling. Passive heating to a Tc of 39.4oC reduced VA by 11 (11)% and MVC by 13 (18)% (P<0.05), but rapid skin cooling, with a concomitant reduction in cardiovascular strain [percentage heart rate reserve decreased from 64 (11)% to 29 (11)%] and psychophysical strain did not restore either of these measures to baseline. Only when cooling lowered Tc back to normal did VA and MVC return to baseline (P<0.05). We conclude that an elevated Tc reduces VA during isometric MVC, and neither Tsk nor cardiovascular or psychophysical strain modulates this response. Results are given as mean (SD) unless otherwise stated.

Keywords

Isometric contraction Maximum voluntary contraction Hyperthermia Fatigue Temperature 

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Shawnda Morrison
    • 1
  • Gordon G. Sleivert
    • 1
    • 2
  • Stephen S. Cheung
    • 3
  1. 1.Human Performance Laboratory, Faculty of KinesiologyUniversity of New BrunswickFrederictonCanada
  2. 2.Director of Sport Science and Medicine, Canadian Sport Centre VictoriaPacificSportVictoriaCanada
  3. 3.Environmental Ergonomics Laboratory, School of Health and Human PerformanceDalhousie UniversityHalifaxCanada

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