Mitigating the impact of cold air exposure on soldier wellbeing and performance

Abstract

Throughout human history there are many stark examples of the toll of cold weather on soldier performance, health, and ultimately survival. Upon exposure to a cold environment a cutaneous vasoconstriction, primarily mediated by reductions in local skin temperature, directs warm blood away from the body shell towards the body core. The resultant decline in peripheral blood flow in extreme cases has been shown to be analogous to the occlusion of blood flow with a blood pressure cuff inflated above arterial blood pressure – leading to a “physiological amputation” of the extremities. In advance of this scenario, vast decrements in manual dexterity, which in a military context can have a profound effect on soldier performance, are observed with peripheral cooling, most likely due to a decline in muscle and joint temperatures as opposed to reductions in nerve conduction velocity. In sub-zero environments the risk of skin freezing is elevated especially if the soldier is required to touch cold objects with high thermal conductivity. The magnitude skin freezing risk is subsequently associated with sex, hand size and the extent that blood flow to the skin is maintained, which itself is determined by both physiological (degree of vasoconstriction) and physical (contact pressure) factors. Factors that mitigate the effects of cold stress include shivering thermogenesis, which has the capacity to increase metabolic rate up to five-fold. However, such responses can heavily impact the capacity to perform fine motor tasks and over a prolonged period can lead to large energy deficits. The capacity to defend body temperature in the cold through shivering is also compromised by the low oxygen partial pressure at high altitude. The rate of body cooling in the cold is strongly influenced by physical factors such as surface area-to-mass ratio and the thickness of subcutaneous fat, and the evidence supporting the notion of a physiological adaptive capacity to repeated cold exposure seems to be scarce. It follows that the most impactful way in which humans can maintain optimal health and performance in the cold is through behavioural adaptations, most notably wearing appropriate clothing, which can be configured to maximize operational performance.