This experiment investigates the validity of six thermometers with different measuring sensors, operation and site of application, to estimate core temperature (Tc) in comparison to an ingestible thermometric sensor based on quartz crystal technology. Measurements were obtained before, during and after exercise in the heat, controlling the presence of air-cooling and skin sweating. Twelve well-trained men swallowed the ingestible thermometer 6 h before the trial. After pre-exercise resting measurements at 20 °C, subjects entered a heat chamber held at 40 °C. Exercise in the heat consisted of 60 min of pedalling on cycle ergometer at 90% of the individually determined first ventilatory threshold. Results reveal that wind and skin sweat invalidate the use of skin infrared thermometry to estimate Tc during exercise in the heat. However, better Tc estimations were obtained in wind-restricted situations. We detected important differences between same-technology devices but different models and brands. In conclusion, there are important limitations to assess Tc accurately using non-invasive thermometers during and after exercise in the heat. Because some devices showed better validity than others did, we recommended using tympanic Braun®, and non-contact skin infrared Medisana® or Visiofocus® in wind-restricted and no sweat conditions to estimate Tc during exercise in the heat.
Keywords: Body temperature; Heat illness; Hyperthermia; Indoor exercise; Rehydration; Thermometric.