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

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.

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.

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 R² 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).

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.