Comparison of gastrointestinal and rectal temperatures during recovery after a warm-weather road race

Context: It has been well established that gastrointestinal temperature (TGI) tracks closely with rectal temperature (TREC) during exercise. However, the field use of T_GI 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 T_GI and T_REC in runners who completed an 11.3-km warm-weather road race and determine if runners with higher T_GI and T_REC 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 T_GI and T_REC 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 T_GI and T_REC, using Bland- Altman analysis, and the 20-minute passive cooling rates for T_GI and T_REC. Results: No differences were evident between T_GI and T_REC throughout passive rest (P=.542). The passive cooling rates for T_GI and T_REC were 0.046 ± 0.0318C· min^-1 and 0.060 ± 0.0368C·min^-1, respectively. Runners with higher T_GI and T_REC 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 T_GI 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, T_GI provided a valid measure of body temperature compared with the criterion measure of T_REC. Therefore, T_GI may be a viable option for monitoring postexercise-induced hyperthermia, if the pill is administered prophylactically.