Passive hyperthermia reduces voluntary activation and isometric force production

• Published in: European journal of applied physiology 2004-05, Vol.91 (5-6), p.729-736
• Main Authors: Morrison, Shawnda, Sleivert, Gordon G, Cheung, Stephen S
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Adolescent; Adult; Body Temperature - physiology; Cold Temperature; Fever - physiopathology; Humans; Isometric Contraction - physiology; Knee Joint - physiology; Male; Muscle, Skeletal - physiology; Physical Endurance - physiology; Physical Exertion - physiology; Psychomotor Performance - physiology; Skin Temperature - physiology; Volition - physiology
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-004-1063-z

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 (T(sk)) and body core temperature ( T(c)) on these factors. Twenty-two males [VO(2max)=64.2 (8.9) ml x 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 degrees C rectal temperature (T(re)) and then cooled back to 37.4(o)C using a liquid conditioning garment. Voluntary strength and VA (interpolated twitch) were examined during an isometric 10-s MVC at 0.5 degrees C intervals during both heating and cooling. Passive heating to a T(c) of 39.4(o)C reduced VA by 11 (11)% and MVC by 13 (18)% (P