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physiological adaptation.* Nonetheless, several changes can be observed to
affect tolerance and performance in cold climates. When tested, fi shermen

who as part of their work routinely immerse their hands in cold water for
several hours a day show a higher finger temperature in response to 10 min

hand immersion in cold water (2.5°C) (“Hunting reaction”; LeBlanc, Hildes &
Heiroux, 1960). In addition, mean arterial blood pressure is reduced (systemic
vascular response). It has also been shown that cold-induced vasodilation
(dilation of peripheral blood vessels to warm an area that has been subjected
to prolonged cold and possible injury) occurs more rapidly in individuals who
routinely work in cold environments (Nelms & Soper, 1962). In whole-body
cold immersion experiments, subjects who routinely work in cold environ-
ments maintain a higher skin temperature than control subjects (LeBlanc,
Pouliot & Rheaume, 1964). Shivering promotes whole-body warmth, but a
shivering body also loses heat to the environment more rapidly. In an apparent

effort to conserve body heat, individuals who routinely work in the cold begin
shivering at lower temperatures (Hong, Lee, Kim, Hong & Rennie, 1969).
Survival in the cold depends on sustained core body temperature, which

can be achieved by increases in metabolic rate. This is also important to man-
ual dexterity and to the prevention of peripheral cold injuries that can result
from vasoconstriction (Stocks, Taylor, Tipton & Greenleaf, 2004). Although

prolonged exposure to extreme cold is often fatal, there are cases in which
human beings have survived with full recovery from gradual core body cool-
ing to less than 15°C (Stocks et al., 2004). This raises the question of what

unique individual attributes and differences might promote physical or psy-
chological resilience to extreme cold. Scientists at the Defense Institute of
Physiology and Allied Sciences (DIPAS) in New Delhi, India, have explored
traditional medicines and wisdom as possible means to extend soldier resil-
ience in extreme environments. Selvamurthy and his colleagues studied the
effects of yogic meditation and physical training on thermoregulation in nor-

mal Indian soldiers (Selvamurthy, Ray, Hegde & Sharma, 1988). In controlled
experiments, they discovered evidence for an increase in core temperature
that could not be explained by changes in heat loss or shivering. Experiments
at this military laboratory are continuing, as they investigate benefi ts of
meditation techniques to enhance soldier physiological resilience ( Harinath
et al., 2004). Such observations lend credence to anecdotes of resilience in
extreme conditions. For example, a Tibetan pilgrim is reported to have
slept in light clothing and without shoes or gloves on a cold mountainside

* Human beings usually wear protective/insulative clothing when they work and exercise
in cold environments. Even in very cold settings, heat load is possible when clothing
prevents the dissipation of heat generated by physical activity. Because clothing helps to
retain generated metabolic heat, it is usually sufficient to maintain core body tempera-
ture without physiological changes.

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