Core temperature measurement during supine exercise: Esophageal, rectal, and intestinal temperatures

Background: The purpose of this study was to characterize intestinal temperature (Tin) in comparison to esophageal (Tes) and rectal temperature (Tre) during supine exercise. Methods: Seven subjects completed a continuous supine protocol of 20 min of rest, 20 min of cycle exercise at 40% peak oxygen consumption ((V)over dotO(2)peak), 20 min of cycle exercise at 65% (V)over dotO(2)peak, and 20 min of recovery. Tes, Tre, and Tin were recorded each min. Results: Temperatures were not different after 20 min of rest, but Tes and Tin were greater than Tre at the end of the 40% (Tes: 37.38 +/- 0.11; Tin: 37.35 +/- 0.06; Tre: 37.20 +/- 0.10 degrees C) and 65% (V)over dotO(2)peak stages (Tes: 37.83 +/- 0.10; Tin: 37.75 +/- 0.05; Tre: 37.63 +/- 0.08 degrees C). After 20 min of recovery, Tes (37.24 +/- 0.011 degrees C) was less than either Tre ol Tin, which were not different from each other (Tin: 37.39 +/- 0.09; Tre: 37.44 +/- 0.09 degrees C). Time to threshold for increased temperature from rest (+0.10 degrees C) for Tes (10.0 +/- 1.1 min) was not different from Tin (14.0 +/- 1.2 min) but less than Tre (15.7 +/- 1.6 min). Time to reach peak temperature was less for Tes (36.6 +/- 1.8 min) than Tin (40.6 +/- 0.9 min) and Tre (41.4 +/- 0.5 min). Similarly, time to a decrease in temperature (-0.10 degrees C) after exercise was less for Tes (3.7 +/- 0.4 min) than Tin (7.1 +/- 1.5 min) and Tre (10.6 +/- 1.9). Conclusions: Measurement of Tin may be an alternative to Tes to measure Tcore specific time points during exercise with an understanding of the slower response of Tin compared with Tes.