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1 School of Human Kinetics, University of Ottawa, Ottawa, Canada
2 Yellow Springs, Ohio, United States
3 1133 Sheppard Avenue W., Head/Human Protection and Performance Group,Defence R&D Canada - Toronto, North York, Canada
4 Ottawa Health Research Institute, Ottawa, Canada
* To whom correspondence should be addressed. E-mail: ojay{at}uottawa.ca.
The aim of this study was to use whole-body calorimetry to directly measure the change in body heat content (
Hb) during steady-state exercise, and compare these values with those estimated using thermometry. The thermometry models tested were the traditional 2-compartment model of "core" and "shell" temperatures, and a 3-compartment model of "core", "muscle" and "shell" temperatures; with individual compartments within each model weighted for their relative influence upon Hb by coefficients subject to a non-negative and a sum-to-one constraint. Fifty-two participants performed 90-min of moderate intensity exercise (40% of VO2peak) on a cycle ergometer in the Snellen air calorimeter, at regulated air temperatures of 24°C or 30°C and a relative humidity of either 30% or 60%. The "core" compartment was represented by temperatures measured in the esophagus (Tes), rectum (Tre) and tympanic membrane (Tty), while the "muscle" compartment was represented by regional muscle temperature measured in the vastus lateralis (Tvl), triceps brachii (Ttb) and upper trapezius (Tut). The "shell" compartment was represented the weighted mean of 12 skin temperatures (Tsk). The whole-body calorimetry data was used to derive optimally fitting 2 and 3-compartment thermometry models. The traditional 2-compartment model was found to be statistically biased, systematically underestimating Hb by 15.5% (SD 31.3) at 24°C and by 35.5% (SD 21.9) at 30°C. The 3-compartment model showed no such bias, yielding a more precise estimate of Hb as evidenced by a mean estimation error of 1.1% (SD 29.5) at 24°C and 5.4% (SD 30.0) at 30°C with an adjusted R-squared of 0.48 and 0.51 respectively. It is concluded that a major source of error in the estimation of Hb using the traditional 2-compartment thermometry model is the lack of an expression independently representing the heat storage in muscle during exercise.
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