Human responses to cold
Human’s wellbeing, performance and health are optimal at thermoneutral temperatures or near to that. Excess cooling or warming of the body results in uncomfortable feeling, loss in performance and negative health effects. The ambient temperature which is felt thermoneutral depends on the amount of clothing and level of physical activity. At rest and without clothing the thermoneutral ambient temperature would be as high as 27°C. For the whole Finnish population the safest outdoor temperature is 14°C. However, with special arrangements (special clothing and suitable level of physical activity) thermal neutrality can be maintained even at -60°C. In those conditions the working capacity would be limited, of course, because of heavy protection.
Exposure to cold stimulates the cold receptors in the skin. The message from the cold receptors is evaluated in the brains and as a result of this interpretation we get thermal sensations. At the same time, our behavior and physiological responses are changed. The most important physiological effect is the dramatic reduction of circulation in the skin, arms, hands and fingers as well as in feet and toes. It decreases heat loss and sustains the temperature in the deeper organs. Unfortunately, at the same time the reduction in circulation speeds up the cooling of hands and feet. Therefore, a good thermal protection of whole body is needed in cold to prevent the reduction in circulation.
Cold also increases blood pressure and therefore the work load of the heart. Light exercise, like slow walking (e.g. 3 km/h) prevents the increase of blood pressure but higher level of exercise increases it again.
Cooling of the body also stimulates heat production by shivering and, at least in some persons, by brown adipose tissue. Shivering starts in the trunk muscles and may extend to limbs, too, if cooling is severe. At first the shivering is sensed only as an increased stiffness of muscles, but in a more severe cooling shivering becomes a visible tremor and shaking. Shivering can triple the heat production or in most severe conditions make it four-fivefold. However, even a moderate physical exercise increases heat production fivefold and maximally more than tenfold.
Physiological adaptation to cold takes ca. 2 weeks. Thereafter cold is felt less stressful, shivering starts later and is weaker. Moreover, circulation is reduced less in cold after adaptation. That is seen especially clearly in the hands which stay warmer in cold-adapted persons – “fisherman’s hands” are developed. Physiological adaptation to cold has to be acquired in the beginning of every cold season, as it disappears in warm season. The only permanent adaptation is experience and knowledge which facilitates a correct behavior in cold.
Capacity for work decreases in cold because of cooling of muscles, joints and nerves and because of the sensations of stress: both force production, endurance, elasticity, manual performance, psychomotor performance and decision making are impaired. Moreover, heavy winter clothing impairs the work capacity because of its weight and bulkiness.
Checking the drillholes before charging in Kevitsa.