[Frontiers in Bioscience S2, 854-865, June 1, 2010]

Cold thermoregulatory responses following exertional fatigue

John W. Castellani, Michael N. Sawka, David W. DeGroot, Andrew J. Young

US Army Research Institute of Environmental Medicine, 15 Kansas Street, Natick, MA, 01760-5007, USA

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Historical perspective
3.1. Field observations
3.2. Concept of "shivering fatigue"
4. Central attenuation of thermoregulation- set point changes
4.1. Multi-stressor studies
4.2. Serial cold-water immersion
4.3. Independent roles of energy deficit, sleep deprivation, and exercise
5. Peripheral Attenuation - effects on heat loss
5.1. Acute exercise
5.2. Chronic exercise
6. Mechanisms of Thermoregulatory Fatigue
6.1. Energy substrates
6.2. Sympathetic nervous system desensitization
6.3. Vasodilator effects
7. Summary
8. Disclaimer
9. References

1. ABSTRACT

Participants in prolonged, physically demanding cold-weather activities are at risk for a condition called "thermoregulatory fatigue". During cold exposure, the increased gradient favoring body heat loss to the environment is opposed by physiological responses and clothing and behavioral strategies that conserve body heat stores to defend body temperature. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and/or repeated cold exposure, fatigue induced by sustained physical exertion, or both together, can impair the shivering and vasoconstrictor responses to cold ("thermoregulatory fatigue"). The mechanisms accounting for this thermoregulatory impairment are not clear, but there is evidence to suggest that changes in central thermoregulatory control or peripheral sympathetic responsiveness to cold lead to thermoregulatory fatigue and increased susceptibility to hypothermia.