Determining the rate of body heat storage by incorporating body composition.

The rate of body heat storage (S) is often used as an index of thermal stress. The traditional approach for determining S assumes that the specific heat (Cp) of all body tissues may be averaged to 0.83 kcal X kg-1 X degrees C-1, irrespective of the actual proportion of different tissues in the body. The present theoretical analysis primarily partitions the body into N compartments. However, this analytical approach involves the difficulty of making an exact evaluation of the mass and temperature of multiple compartments. Therefore, by adopting a two-compartment (core and shell) model, the specific heat capacities, mass fractions, and changes in the temperatures of the two compartments are combined, and S is defined as a function of adiposity (= mass fraction of peripheral tissues). Evaluation of a newly developed equation showed close agreement with observations during a series of cold-water immersion trials, and indicated that the new approach seems to adequately predict S as related to body composition.