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 duration: 3.5 to 8 min
|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.|
|power density||100 mW/cm²||-||-||-||-|
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.