Bohyun Kim

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  Student Presentation: Effect of Locomotion on Body Temperature Control Mechanism
  Bohyun Kim

  We created a mathematical model to describe core (body) temperature responses to exercise at different ambient temperatures based on an experiment data. In the experiment, rats were forced to run on a treadmill at different speeds. Their core temperature time-series were recorded during 15 min runs with speeds 0, 6, 12, and 18 m/min at 0 incline in cool (24°C, T1) and hot (32°C, T2) environment. At T1 there was a temperature drop during first 5 min, while at T2 temperature did not change during that period. After 5 min, temperature started rising linearly at both T1 and T2 until the treadmill was stopped. The slope of this linear increase remained constant for all four speeds at T1, whereas at T2 it progressively steepened with the speed increase. To explain these findings, we have designed a model which consisted of two body components exchanging heat: the core and muscles. The core dissipated heat proportionally to difference between the core and ambient temperatures. This model was formally described by a system of two differential equations. All parameters of the system were subject to fit the average temperature response curves obtained from the experiment. Hypothermia during the first 5 min at T1 was interpreted as a result of decreased thermogenesis in the core to compensate for the heat generated by locomotion on the treadmill. This drop was not observed at T2 because heat production in the core was too small, and no further decrease was possible. The linear increase of core body temperature after 5 min was a result of heat generation in muscles. We hypothesize that exercise activates thermoregulatory inhibition of thermogenesis and/or increases heat dissipation, which prevents excessive heat accumulation during exercise in cool environment. However, at high ambient temperature this thermoregulatory compensation is impossible because the core metabolism cannot be reduced any further, while heat dissipation is already at its maximum. Therefore, heat generation by exercise added to heat accumulation and presented itself as an increased rate of the temperature growth. We conclude that compensatory mechanisms in the thermoregulatory system may underlie some controversial results concerned with the role of locomotion in the body temperature dynamics.