Estimating changes in mean body temperature for humans during exercise using core and skin temperatures is inaccurate even with a correction factor

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Abstract
Changes in mean body temperature (ΔT̄b) estimated by the traditional two-compartment model of “core” and “shell” temperatures and an adjusted two-compartment model incorporating a correction factor were compared with values derived by whole body calorimetry. Sixty participants (31 men, 29 women) cycled at 40% of peak O2 consumption for 60 or 90 min in the Snellen calorimeter at 24 or 30°C. The core compartment was represented by esophageal, rectal (Tre), and aural canal temperature, and the shell compartment was represented by a 12-point mean skin temperature (T̄sk). Using Tre and conventional core-to-shell weightings ( X) of 0.66, 0.79, and 0.90, mean ΔT̄b estimation error (with 95% confidence interval limits in parentheses) for the traditional model was −95.2% (−83.0, −107.3) to −76.6% (−72.8, −80.5) after 10 min and −47.2% (−40.9, −53.5) to −22.6% (−14.5, −30.7) after 90 min. Using Tre, X = 0.80, and a correction factor ( X0) of 0.40, mean ΔT̄b estimation error for the adjusted model was +9.5% (+16.9, +2.1) to −0.3% (+11.9, −12.5) after 10 min and +15.0% (+27.2, +2.8) to −13.7% (−4.2, −23.3) after 90 min. Quadratic analyses of calorimetry ΔT̄b data was subsequently used to derive best-fitting values of X for both models and X0 for the adjusted model for each measure of core temperature. The most accurate model at any time point or condition only accounted for 20% of the variation observed in ΔT̄b for the traditional model and 56% for the adjusted model. In conclusion, throughout exercise the estimation of ΔT̄b using any measure of core temperature together with mean skin temperature irrespective of weighting is inaccurate even with a correction factor customized for the specific conditions.