Human behavioral temperature regulation : an exercise approach : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph.D.), School of Sport and Exercise, Massey University, Palmerston North, New Zealand

Abstract

Behavior represents our most preferred and effective modality by which body temperature is regulated. However, knowledge concerning the control of this behavior in humans is relatively limited. Therefore, the overall purpose of this thesis was to further our understanding of the control of human thermoregulatory behavior. This was accomplished by firstly establishing self-paced exercise and heat stress as a thermal behavioral model, while secondly the control of this behavior was investigated. In the first part of this thesis, voluntary reductions in exercise intensity have been found to be associated with thermal discomfort and reductions in heat production, which presumably improved heat exchange between the body and the environment over time, and ultimately aided body temperature regulation. Thus, these experimental data associatively indicate that reductions in exercise intensity in the heat are thermoregulatory behaviors, suggesting that self-paced exercise in the heat is a valid model by which to evaluate human thermal behavior. The studies presented in the second part of this thesis systematically evaluated the control of this behavior. It was subsequently demonstrated that skin temperature and the accompanying alterations in thermal perception and the percentage of peak oxygen uptake elicited by a given exercise intensity are all modulators of exercise intensity, and thus thermal behavior, in the heat. Notably, reductions in peak oxygen uptake appear to play a minimal role. Importantly, these studies strengthened the associations observed in the first part of this thesis by specifically establishing a causative relationship between exercise intensity and temperature regulation. Furthermore, the experimental observations also indicated that thermal behavior during self-paced exercise is ultimately initiated by the perception of effort response. In conclusion, the findings presented in this thesis suggest that a voluntary reduction in exercise intensity occurring in the heat is a thermoregulatory behavior, and that this behavior can be directly elicited by changes associated with elevations in skin temperature. During such instances, thermal perception and the percentage of peak oxygen uptake elicited by a given exercise intensity have been uniquely identified as contributors to this behavior. The findings of this thesis improve our understanding of the control of human thermoregulatory behavior.