A comparison of rectal, oesophageal and gastro-intestinal tract temperatures during moderate-intensity cycling in temperate and hot conditions

The purpose of this study was to compare three of the most commonly used methods of core temperature (T-core) measurement during cycling under different environmental conditions as there are practical problems associated with each method and, sometimes, uncertainty as to which is the appropriate measure. Eight trained males ((V) over dotO(2)max: 60 +/- 7 ml kg(-1) min(-1)) completed two 60-min cycling trials at similar to 70% (V) over dotO(2)max at 20 degrees C (MOD) and 35 degrees C (HOT). Measures of T-core were made every 5 min with oesophageal (T-oes) and rectal (T-rec) thermistors and of the gastro-intestinal tract temperature (T-gi) with a temperature-sensitive disposable radio pill. During MOD T-oes initially plateaued after 10 min, T-gi after 25 min and T-rec after 50 min, whereas during HOT these times had increased to 25 min for T-oes and 55 min for both T-gi and T-rec. T-oes consistently provided lower readings than T-rec (0.24-0.26 degrees C) and T-gi (0.26-0.28 degrees C) with T-gi and T-rec similar (0.02 degrees C). Readings for T-gi displayed closer agreement with T-rec (ICC = 0.92) than T-oes (ICC = 0.86) with less agreement between T-rec and T-oes (ICC = 0.84). 95% of all T-gi readings were within +/- 0.5 degrees C of T-rec and within +/- 0.6 degrees C of T-oes with 95% of all T-oes readings being within +/- 0.7 degrees C of T-rec. These results demonstrate distinct response times, absolute values and agreement between T-core measured at different body locations under different ambient conditions. Implications and considerations are discussed.