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This Article Full Text Full Text (PDF) All Versions of this Article: 107/5/1519    most recent 00577.2009v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Ely, B. R. Articles by Montain, S. J. PubMed PubMed Citation Articles by Ely, B. R. Articles by Montain, S. J.

Evidence against a 40°C core temperature threshold for fatigue in humans

¹Thermal and Mountain Medicine Division and ; ²Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, Massachusetts

Submitted 29 May 2009 ; accepted in final form 20 August 2009

Evidence suggests that core temperatures of 40°C can induce fatigue, although this may be confounded by coincident elevations in skin temperatures and maximal cardiovascular strain. In an observational field study to examine core temperature threshold for fatigue, we investigated whether running performance is impaired when rectal temperature (T_re) is >40°C and skin temperature remains modest. Seventeen competitive runners (7/10 women/men: 8 km best 1,759 ± 78/1,531 ± 60 s) completed 8-km track time trials in cool (WBGT 13°C; n = 6), warm (WBGT 27°C; n = 4), or both (n = 7) conditions. T_re, chest skin temperature, and heart rate were logged continuously; elapsed time was recorded every 200 m. Running velocity for T_re >40°C was compared with that for T_re <40°C for each runner. Changes in running velocity over the last 600 m were compared between runners with T_re >40°C and <40°C. Twelve runners achieved T_re >40.0°C with 600 m remaining (range 600–3,400 m). Average running velocity for T_re <40°C (282 ± 27 m/min) was not different from that for T_re >40°C (279 ± 28 m/min; P = 0.82). There were no differences in running velocity during the final 600 m between runners with final T_re >40°C or <40°C (P = 0.16). Chest skin temperature ranged from 30 to 34°C, and heart rate was >95% of age-predicted maximum. Our observation that runners were able to sustain running velocity despite T_re >40°C is evidence against 40°C representing a "critical" core temperature limit to performance.

ambient temperature; pacing; performance; body temperature