Context: It has been well established that gastrointestinal temperature (TGI) tracks closely with rectal temperature (TREC) during exercise. However, the field use of TGI pills is still being examined, and little is known about how measurements obtained using these devices compare during recovery after exercise in warm weather. Objective: To compare TGI and TREC in runners who completed an 11.3-km warm-weather road race and determine if runners with higher TGI and TREC present with greater passive cooling rates during recovery. Design: Cross-sectional study. Setting: Field. Patients or Other Participants: Thirty recreationally active runners (15 men, 15 women; age = 39 ± 11 years, weight = 68.3 ± 11.7 kg, body fat = 19.2% ± 5.0%). Main Outcome Measure(s): The TGI and TREC were obtained immediately after the race and during a 20-minute passive rest at the 2014 Falmouth Road Race (heat index = 26.28C ± 0.98C). Temperatures were taken every 2 minutes during passive rest. The main dependent variables were mean bias and limits of agreement for TGI and TREC, using Bland- Altman analysis, and the 20-minute passive cooling rates for TGI and TREC. Results: No differences were evident between TGI and TREC throughout passive rest (P=.542). The passive cooling rates for TGI and TREC were 0.046 ± 0.0318C· min-1 and 0.060 ± 0.0368C·min-1, respectively. Runners with higher TGI and TREC at the start of cooling had higher cooling rates (R = 0.682, P , .001 and R=0.54, P=.001, respectively). The mean bias of TGI during the 20-minute passive rest was -0.068C ± 0.568C with 95% limits of agreement of 61.098C. Conclusions: After participants completed a warm-weather road race, TGI provided a valid measure of body temperature compared with the criterion measure of TREC. Therefore, TGI may be a viable option for monitoring postexercise-induced hyperthermia, if the pill is administered prophylactically.
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