Umbilical temperature correlation with core and skin temperatures at rest, in the heat and during physical activity.

Purpose: to determine the correlation of umbilical temperatures (T _umb ) with simultaneously recorded chest wall temperature (T _chest ) and rectal temperature (T _rectal ) in adults during rest, heat exposure and exercise.
Methods: A total of 28 healthy men, wearing different types of clothing (athletic garb, a spandex full body heating garment, firefighter bunker gear) had average and peak umbilical, chest wall and rectal temperature measurements taken during sedentary temperature stabilisation stages, heat exposure periods and active exercise phases.
Results: Curvilinear relationships were noted between T _chest and T _umb compared with T _rectal and their association became noticeably positive and linear at approximately 35.5 °C. Polynomial regression analysis of T _rectal with linear and quadratic forms of T _chest and T _umb indicated an overall R ² of 0.657 and 0.767, respectively. Bivariate analysis of a restricted data set (where T _chest and T _umb  ≥35.5°), indicated that T _umb was significantly associated with T _rectal (r _average  = 0.710, p <0.001; r _peak   = 0.841, p <0.001) and T _chest was also significantly associated with T _rectal , but less so (r _average  = 0.570, p <0.001; r _peak  = 0.699, p <0.001).
Conclusions: the umbilicus offers a non-invasive, peripheral site for measurement of temperature that more closely correlated with body core temperature than T _chest when core temperature was ≥35.5 °C.