Modeling the body temperature throughout the day with a two-term function

A two-term function with potential and exponential terms is proposed to model the body temperature throughout the day. These terms can be related to thermogenic and thermolytic processes that are opposite but simultaneous. The first term, a potential function, reflects that the heat gain process is predominant; the second term is a negative exponential function and reflects the predominance of heat dissipation. The function also provides the time of the inflection between thermal opposite processes. The proposed two-term function and a cosine function were fitted to 335 temperature series of 24-h duration recorded in humans and animals. The percentage of variance accounted for by the two-term function was higher than that for the cosine approximation for the total sample and for those series whose shape was asymmetrical (n = 75). Nevertheless, no significant differences between the percentage of variance accounted for by the two functions were found for those series whose shape was symmetrical (n = 260). The results of different subgroups that differed in experimental conditions are discussed.