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

2009; American Physiological Society; Volume: 107; Issue: 5 Linguagem: Inglês

10.1152/japplphysiol.00577.2009

8750-7587

Brett R. Ely, Matthew R. Ely, Samuel N. Cheuvront, Robert W. Kenefick, David W. DeGroot, Scott J. Montain,

Climate Change and Health Impacts

Evidence suggests that core temperatures of approximately 40 degrees 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 degrees 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 approximately 13 degrees C; n = 6), warm (WBGT approximately 27 degrees 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 degrees C was compared with that for T(re) 40 degrees C and 40.0 degrees C with >or=600 m remaining (range 600-3,400 m). Average running velocity for T(re) 40 degrees 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 degrees C or 95% of age-predicted maximum. Our observation that runners were able to sustain running velocity despite T(re) >40 degrees C is evidence against 40 degrees C representing a "critical" core temperature limit to performance.