Study type: Medical/biological study (experimental study)

Exercise in the heat is limited by a critical internal temperature. med./bio.

Published in: J Appl Physiol 2000; 89 (2): 799-806

Aim of study (acc. to author)

To test the hypothesis that a critical internal temperature limits exercise in the heat. Microwaves were used to rapidly heat rats before treadmill exercise to exhaustion. Rats were preheated to three levels (low, medium, and high).



Exposure Parameters
Exposure 1: 2.1 GHz
Exposure duration: 3.5 to 8 min

General information


Exposure 1

Main characteristics
Frequency 2.1 GHz
Exposure duration 3.5 to 8 min
Additional info More details on the MW exposure are given in the following article: Robinson SM and Blatt WF. Heat tolerance of the resting and exercising rat. Can J Physiol Pharmacol 46: 189-194, 1968.
Exposure setup
Exposure source
Chamber Anachoic chamber
Setup rats placed into restrainers.
Measurand Value Type Method Mass Remarks
power density 100 mW/cm² - - - -

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Run time to exhaustion was significantly reduced after preheating. There was a significant negative correlation between run time and initial hypothalamic and rectal temperature. The temperatures at exhaustion were not significantly different across treatments, with a range of 41.9-42.2°C (hypothalamic temperature) and 42.2-42.5°C (rectal temperature). There were no significant differences in run time in the sham runs. Body weight the day after each treatment was unaffected.
Because the temperatures at exhaustion were virtually identical, whereas the run times to exhaustion were correlated with the initial temperatures, this investigation provides strong evidence that exercise is limited by the attainment of a critical internal temperature.

Study character:

Study funded by