Regulation of Body Temperature by Autonomic and Behavioral Thermoeffectors Zachary J. Schlader and Nicole T. Vargas Center for Research and Education in Special Environments, Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY SCHLADER, Z.J. and N.T. VARGAS. Regulation of body temperature by autonomic and behavioral thermoeffectors. Exerc. Sport Sci. Rev., Vol. 47, No. 2, pp. 116–126, 2019. Thermoregulation is accomplished via autonomic and behavioral responses. Autonomic responses may influence decisions to behaviorally thermoregulate. For instance, in addition to changes in body temperature, skin wettedness and involuntary muscle contraction, which occur subsequent to sweating and shivering, likely modulate thermal behavior. This autonomic- behavioral interaction provides the rationale for our hypothesis that thermoregulatory behavior decreases the requirement for autonomic responses. Key Words: temperature regulation, thermoregulation, skin blood flow, sweating, shivering, skin wettedness, thermal discomfort Key Points • Body temperature is regulated via both autonomic and be- havioral thermoeffectors. • Current evidence indicates that thermal behavior decreases the requirement for autonomic thermoeffector responses. This suggests that autonomic thermoeffector activation may contribute to decisions to behaviorally thermoregulate. • Thermal behavior requires an increase in subjective ther- mal discomfort, the likes of which are perceived from afferent feedback stemming from thermoreceptor activation. There is no evidence that efferent autonomic thermoeffector activity can be perceived directly. • Thus, the autonomic thermoeffector end-organ response, manifested in changes in skin temperature (occurring sec- ondary to changes in skin blood flow), skin wettedness (oc- curring secondary to sweating), or shivering, is consciously perceived to magnify perceptions of thermal discomfort and stimulate thermal behavior. INTRODUCTION The frequency and intensity of heat waves are predicted to increase in the coming decades, while periodic cold waves will still persist. Heat and cold waves pose a threat to human health, particularly in at-risk populations, such as children, older adults, and those with chronic diseases (e.g., diabetes, cardiovascular disease, etc.). As a result, a comprehensive understanding of hu- man temperature regulation and its integration with other reg- ulatory systems (e.g., blood pressure, metabolism, etc.) in healthy and at-risk populations is both important and timely. Temperature regulation in humans is achieved via autonomic and behavioral thermoeffectors. Autonomic thermoeffectors pro- mote heat loss, heat conservation, or heat gain. This occurs by modifying radiative and convective heat exchange via changes in skin blood flow, promoting evaporative heat loss via sweating or increasing metabolic heat production by increasing shivering or nonshivering thermogenesis. Behavioral thermoeffectors are movements aiming to establish a thermal environment or mi- croclimate that ultimately promotes heat balance. In humans, behavioral thermoeffectors are wide ranging and include “sim- ple” actions, such as putting on or removing a coat, and more “complex” actions, such as developing and seeking shelters with well-equipped heating or cooling systems. It has long been appreciated that behavior is the most pow- erful and diverse thermoregulatory response (1). For example, behavior enables the regulation of body temperature while inhabiting extreme locations that otherwise exceed the capac- ity of autonomic responses (e.g., winter in Buffalo, NY). The autonomic thermoregulatory responses and the mechanisms underlying their respective reflex arcs are well described. By contrast, less is known regarding the mechanisms and modula- tors of human behavioral thermoregulation. This includes a lack of information regarding precisely how autonomic and be- havioral thermoeffectors seamlessly work together to regulate body temperature (2). The importance of this shortcoming is highlighted by predictions that the magnitude of forecasted heat stress in the coming decades may exceed the limits of Address for correspondence: Zachary J. Schlader, Department of Exercise and Nutrition Sciences, University at Buffalo, 204A Kimball Tower, Buffalo, NY 14214 (E-mail: zjschlad@buffalo.edu). Accepted for publication: October 11, 2018. Editor: Dave Hostler, Ph.D., EMT-P, DMT, FACSM. 0091-6331/4702/116–126 Exercise and Sport Sciences Reviews DOI: 10.1249/JES.0000000000000180 Copyright © 2019 by the American College of Sports Medicine 116 ARTICLE Copyright © 2019 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.