The Effects of Heat and Cold on Cognitive Function and Endurance Capacity

Abstract

The maintenance of mental and physical function in hot and cold environments is more challenging compared to thermoneutral environments due to increases systemic physiological and psychological strain. The mechanism for impairments in both cognitive and physical function may be due to early perturbations in whole-body heat balance where the change in skin temperature (even before measurable changes in core temperature) impair performance, followed by greater impairments with changes in core temperature. However, the separate and combined effects of changes in skin and core temperature over a range of cognitive functions and exercise require further elucidation. Therefore, this dissertation tested cognitive function (psychomotor processing, working memory, and executive function) and endurance capacity (at 70% of peak power output) over a range of skin and core temperatures and thermal conditions. Chapter 4 investigates the effects of whole-body skin and core warming (hyperthermia) on cognitive function. In addition, the pharmacological drug, methylphenidate (20 mg, dopamine re-uptake inhibitor) was used as it may improve physiological and psychological strain during heat stress. Chapter 5 built upon Chapter 4 by testing the effects of whole-body skin and core cooling (mild hypothermia) on cognitive function. Chapter 6 extended the findings of Chapter 5 by testing the effects of whole-body skin and core cooling on endurance capacity, to potentially see a cognitive-physical performance interaction. Collectively, we found that neither changes in skin temperature (Range: ∆-6 to +4.5°C), without changes in core temperature, nor manipulation of core temperature (Range: ∆-0.8 to +1.5°C) significantly impaired cognitive function in hot or cold environments (Chapters 4 & 5). Furthermore, methylphenidate did not enhance cognitive function. Whereas, endurance capacity was significantly influenced by cold stress, where cooling the skin/outer shell impaired performance by 32%, while core cooling of ∆-0.5C and ∆-1.0C from baseline temperature further impaired performance by 61% and 71% respectively. There were no differences between the two core cooling conditions. Collectively, this research program demonstrates the capacity to maintain cognitive function, but not physical capacity under thermal strain. From a practical standpoint, interventions should focus to minimize cold strain to prevent declines in physical capacity under cold conditions.